bioactivity of essential oils as green biopesticides ......eo- based pesticides find their way to...

1 Department of Parasitology, Faculty of Veterinary Medicine, Benha University,Moshtohor 13736, Egypt.

* Corresponding author: E-mail: [email protected]

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Bioactivity of Essential Oils as GreenBiopesticides: Recent Global Scenario

HANEM FATHY KHATER1*

ABSTRACT

Plant essential oils (EOs) are produced commercially from several botanicalsources, mainly form members of the mint family. Some EOs have beenrecognized as a natural source of pesticides as they have many compoundsthat adversely affect growth and development and alter feeding, matingand oviposition behaviors. EO- based pesticides find their way to the marketand their stability can be influenced through microencapsulation ornanoencapsulation. EOs are advantageous due to their low mammaliantoxicity, eco-safety, no development of resistance, low cost of the activeingredients, reduced number of applications, higher popularity with organicgrowers and environmentally conscious consumers, and suitability for urbanareas, homes and other sensitive areas such as schools, restaurants andhospitals. EOs can be used as alternative to synthetic insecticides or alongwith other insecticides under integrated pest control management for pestsof medical, veterinary and agriculture importance. Thus, essential oils couldmake their way from the traditional into the modern insecticidal domain.

Key words: Pest control, Green pesticides, Commercialization, Modeof action, Microencapsulation, Nanoencapsulation

154 RPMP Vol. 37—Essential Oils–II

INTRODUCTION

With a greater awareness of the hazards associated with the use ofsynthetic organic insecticides, (Sanchez-Bayo, 2011; Sheikh, 2011),essential oils (EOs) could be suitable alternative products for pestcontrol. EOs are extracted from various aromatic plants generallylocalized in Mediterranean and tropical countries where they representan important part of the traditional pharmacopoeia. They are usuallyobtained by steam or hydro-distillation.

The ancient Egyptians may have been the first to discover thepotential of fragrance. They created various aromatic blends, both forpersonal use and for ceremonies performed in the temples and pyramids.The Egyptians were masters in using essential oils and other aromaticsin the embalming process. Historical records indicate that one of thefounders of “pharaonic” medicine was the architect Imhotep, who wasthe Grand Vizier of King Djoser (2780 – 2720 B.C.). Imhotep is often

Fig. 1: Global scenario on the Bioactivity of Essential Oils as GreenPesticides, designed by Eslam Afify, Different, Benha, Egypt

Fig. 2: Nefertiti offering essential oils to Isis

155Bioactivity of Essential Oils as Green Biopesticides

given credit for ushering in the use of oils, herbs and aromatic plantsfor medicinal purposes.

EOs also developed in the middle Ages by Arabs. EOs are known fortheir antiseptic, medicinal properties and their fragrance. In addition,they are used in embalmment, preservation of foods and asantimicrobial, analgesic, sedative, anti-inflammatory, spasmolytic andlocally anesthetic remedies. In recent times, approximately 3000 volatileoils are known, 300 of which are produced commercially forpharmaceutical, sanitary, cosmetic, perfume, agricultural and foodindustries (as food preservers and additives) and their mechanisms ofaction have been revealed, particularly at the antimicrobial andinsecticidal levels.

Botanicals have been traditionally used for protection of storedcommodities in the Mediterranean region and in southern Asia, butinterest in EOs was renewed with emerging demonstration of theirfumigant and contact insecticidal activities to a wide range of pests inthe 1990s. More particulars about EOs and their constituents as greeninsecticides will be highlighted in the present work.

CHEMICAL CONSTITUENTS

EOs are volatile with strong odor found in several plant families, suchas Myrtaceae, Lauraceae, Rutaceae, Lamiaceae, Asteraceae, Apiaceae,Cupressaceae, Poaceae, Zingiberaceae and Piperaceae. EOs can besynthesized by all plant organs, such as buds, flowers, leaves, stems,twigs, seeds, fruits, roots, wood or bark. They are liquid, volatile, limpidand rarely cultured, lipid soluble and soluble in organic solvents with agenerally lower density than that of water.

The oils are generally composed of complex mixtures ofmonoterpenes, biogenetically related phenols, and sesquiterpenes, forinstance, 1,8-cineole, the major constituent of oils from rosemary,Rosmarinus officinale (Rs. officinale) and eucalyptus, Eucalyptus globus(Eu. globules); eugenol from clove oil, Syzygium aromaticum (Sy.aromaticum); thymol from garden thyme, Thymus vulgaris (Th.vulgaris); and menthol from various species of mint (Mentha species)(Isman, 1999). The chemical composition and broad spectrum ofbiological activities for EOs can vary with plant age, the plant tissues,geographical origin of the plant, the organ used in the distillationprocess, the type of distillation, and the species and age of a targetedpest organism (Chiasson et al., 2001). The variety of types and levels ofactive constituents in each oil may be responsible for the variability in


their potential against pests. Valuable reviews on the chemicalconstituents of EOs are those of Edris (2007), Ebadollahi (2011) andKhater (2012).

MODE OF ACTION

Essential oils protect plants as they act as antibacterials, antivirals,antifungals, insecticides and also against herbivores by reducing theirappetite for such plants. EOs interfere with basic physiological,behavioral, metabolic, and biochemical functions of insects as insectsinhale, ingest or skin absorb EOs. EOs provoke rapid action againstsome pests indicating a neurotoxic mode of action. EOs disturb thefunction of octopamine which generate a total breakdown of the nervoussystem in insects. Octopamine is a biogenic amine found in insects andacts as a neurotransmitter, neurohormone and circulatingneurohormone–neuromodulator. Octopamine exerts its effects throughinteracting with at least two classes of receptors, octopamine-1 andoctopamine-2 (Evans, 1980).

Studies on cultured cells of the American cockroach, Periplanetaamericana (Pr. americana) and brains of Drosophila melanogaster (Drs.melanogaster) demonstrated that eugenol mimics the action ofoctopamine and increases intracellular calcium levels. The role of theoctopaminergic system in the cytotoxicity of EOs was also demonstratedin cultures of epidermal cells of Helicoverpa armigera. Tyramine (aprecursor of octopamine) receptors are also involved in the recognitionof monoterpenes such as thymol, carvacrol, and -terpineol in Drs.melanogaster. These monoterpenes influence the production of cyclicAMP (cAMP) and calcium at the cellular level. (See Regnault-Roger etal. (2012) for more details).

Investigation of the formamidine insecticides revealed sublethalbehavioral and physiological effects, probably mediated by theoctopaminergic nervous system (Matsumura & Beeman, 1982).Sublethal effects, ex. feeding deterrence, repellency, were observedwith some of the EO compounds may be consistent with this mode-of-action.

The lack of octopamine receptors in vertebrates likely accounts forthe profound mammalian selectivity of EOs as insecticides (i.e., EOsare toxic to insects but not to mammals); therefore, the octopaminergicsystem of insects represents a biorational target for insect controlstrategies (Enan et al., 1998).


In addition to octopamine receptors, Huignard et al. (2008) describeseveral different types of receptors, including gamma aminobutyric acid,GABA-gated neurons, which are target sites of the compounds. Thymolbinds to GABA receptors associated with chloride channels located onthe neurotransmitter analogous to the vertebrate noradrenalinemembrane of postsynaptic neurons and disrupts the functioning ofGABA synapses (Priestley et al., 2003). Monoterpenoids also inhibitacetylcholinesterase enzyme activity as the major site of action in insects(Rajendran & Sriranjini, 2008).

Volatile oils reduce egg hatchability as oil vapors are toxic to eggs(Moawad & Ebadah, 2007; Khater et al., 2009) or as a result of chemicalingredients which may diffuse into eggs, thus affecting vital processesassociated with embryonic development (Schmidt et al., 1991). The ovicidaland deterrent effects of EOs could be utilized in prophylaxis against insectinfestation especially against myiasis infestations (Khater & Khater, 2009;Khater et al., 2011) and stored product pests (Khater, 2011; 2012).

Some of the EOs and their components induce chemosterilantactivity, making the insect pests sterile. The compound -asaroneextracted from rhizomes of Acorus calamus (Ac. Calamus), possessesantigonadial activity causing the complete inhibition of ovariandevelopment of different insects (Varma & Dubey, 1999).

In addition to direct toxicity and chemosterilant activity, EOs induceoviposition and feeding deterrence, repellence and attraction, fumigantand sterilizing effects. Moreover, some oils cause larvicidal effect andthe capacity to delay development and suppress emergence of adults(Khater, 2003; Shalaby & Khater, 2005; Khater & Shalaby, 2008; Khater& Khater, 2009; Khater et al., 2009, 2011; Khater, 2011; 2012).

Some EOs are useful against pests that are resistant towards syntheticpesticides because EOs are a complex mixture of components includingminor constituents, whereas synthetic pesticides are based on singleproducts. Components of Eos act synergistically within the plant as adefense strategy. Hence, it is likely that they are more durable towardspests evolving resistance (Feng & Isman, 1995). The mode of actions ofEOs have been reviewed in details by Bakkali et al. (2008), Khater (2011,2012), and Regnault-Roger et al. (2012).

BEHAVIORAL INSECT CONTROL

Some plants contain chemicals which alter the behavior and life cycleof insect pests without killing them. Such chemicals are termed as


“semio-chemicals” by the organization for Economic Cooperation andDevelopment. Plants with strong smells act as repellents and can protectthe crops nearby and called “companion plants” such as French marigoldand coriander. Behavioral insect control is based on repellents andattractants, whereby a given species is either repelled from a host plantby a repulsive agent or attracted to a bait or pheromone.

A Push–Pull or stimulo–deterrent diversionary strategy has beendeveloped in South Africa for minimizing damage due to maize stemborer insects (Cook et al., 2006). This strategy involves the selection ofplant species employed as trap crops to attract stem borer insects awayfrom maize crops, or some plant species are used as intercrops to repelinsects. Pennisetum purpureum and Sorghum vulgare attract the stemborer insect, while Milinis minutiflra, Desmodium uncinatum andDesmodium intorium are the repellent plants. Moreover, the Push–Pull strategy is also employed in the control of Heliothis sp. in cottonfields. Such strategy exploiting the chemical ecology of plants wouldprove an interesting, indigenous and readily available concept in themanagement of insect population in field crops.

Repellent Effect

Insect repellents are an alternative way to the use of insecticides throughapplication to the skin for protection of an individual from the bites ofmosquitoes, mites, ticks and lice. Moreover, repellents may be used toexclude insects from an area, such as in packaging to prevent infestationof stored products. The first use of repellents goes back into the mistsof time. Herodotus reported the use of strong smelling substances onthe skin amongst the ancient Egyptians. The use of repellents by civilianand military travellers may reduce the occurrence of local diseaseincidences in temperate areas.

One of the widely used synthetic insect repellents is DEET, N, N-diethyl-m toluamide which is generally considered the “gold standard”repellent, providing long-lasting protection of up to 8 hours from timeof application. Unfortunately, it may cause environmental and humanhealth risks, which have been reviewed in details by Khater (2012).There are some rare reports of severe reactions in people, besidesDEET melts plastics causing spoilage of equipment, such as glassesand mobile phones, and many consumers find the odor and sensationon the skin unpleasant (Logan et al., 2010). Accordingly, naturalrepellents attracted the attention of researches as safe and ecofriendlyalternatives to synthetic chemicals.


Ticks detect repellents on the tarsi of the first pair of legs (Haller’sorgan) and insects detect the same substances on the antennae. Thesestructures are thought to be serially homologous between the two classes.Furthermore, the differences in sensitivity to repellents between differentclasses, orders and families are differences of degree only; no fundamentaldifferences in the type of response are observed (Rutledge et al., 1997).

Repellent metabolites

Over the centuries, more plant extracts, particularly essential oils, havebeen described as insect repellents. The best known repellent iscitronella oil, which is obtained from various Cymbopogon species(Gramineae), e.g. Cymbopogon nardus (Cy. nardus). Citronella oilconsists mainly of citronellal ((3,7-dimethyl-oct-6-enal) and geraniol (3,7-dimethyl- octa-2,6(2,7)-dien-1-ol) (Büchel, 1970). Both components arealso effective alone (citronella, e.g. Cockcroft et al., 1998; geraniol, e.g.Mumcuoglu et al., 1996).

Structure-activity relationships of repellents indicate that when aninsect repellent incorporates a ring structure, there is often a carbonylgroup immediately removed from the ring. Most insect repellents arevolatile terpenoids, such as terpenen-4-ol. Other terpenoids can act asattractants. In some cases, the same terpenoid can repel certainundesirable insects while attracting more beneficial insects to favorthe dispersion of pollens and seeds, ex., geraniol repels house flies whileattracting honey bees (Duke, 1990).

Acyclic or monocyclic monoterpenes are small-volatile molecules.They are therefore involved in the transmission of airborne signals fromplants to insects. In the sensilla of insects, specialized odorant bindingproteins (OBPs) respond to volatile monoterpenes. For example, trichoidsensilla of the female silkworm, Bombyx mori, respond to linalool(Picimbon et al., 2008).

Most of the arthropod-repellent compounds are oxygenated, havingthe hydroxyl group linked to a primary, secondary or aromatic carbon.More importantly, some metabolites with the hydroxyl group linked toa tertiary carbon (linalool, -terpineol and limonene), such activity issuppressed against Anopheles gambiae (An. gambiae), suggesting thepossibility that the type of carbon where the hydroxyl substitution ispresent modulates repellency.

Some metabolites are responsible for the repellent activity of EOssuch as -pinene, isolated from the EO of Dianthus caryophyllum,against ticks, Ixodes ricinus (Ix. ricinus), monoterpenes (-pinene,


cineole, eugenol, limonene, terpinolene, citronellol, citronellal, camphor,and thymol) against mosquitoes; and sesquiterpenes, -caryophyllene,repellent against Aedes aegypti (Ae. aegypti); phytol, a linear diterpenealcohol, against An. gambiae; phenylethyl alcohol, -citronellol,cinnamyl alcohol, geraniol.

Patterns of sensitivity were similar among some chemicals ofunrelated structure, but some differences existed between the sensitivityto compounds of similar structure. Observed non-correlation of structurewith activity suggests that repellent tolerances may be non-adaptive;i.e. evolved by random drift of selectively neutral mutations (Rutledgeet al., 1997). For reviews, see Peterson & Coats (2001), Nentwig (2003),Nerio et al. (2010); Dubey et al. (2011); Khater (2011, 2012), andRegnault-Roger et al. (2012).

SYNERGISTIC PHENOMENA

In the context of synergism between the components of EOs, they arecomplex mixtures of numerous molecules and the activity of the maincomponents is modulated by other minor molecules. It is expected thatseveral components of the EO take part in defining the fragrance, thedensity, the texture, the color, cell penetration, lipophilic or hydrophilicattraction, fixation on cell walls and membranes, and cellulardistribution. This last trait is very important because the distributionof the oil in the cell determines the different types of radical reactionsproduced, depending on their compartmentation in the cell. As a result,it is more useful to study an entire oil rather than some of its maincomponents, e.g., terpineol, eugenol, thymol, carvacrol, carvone,geraniol, linalool, citronellol, nerol, safrole, eucalyptol, limonene,cinnamaldehyde.

It is worthy to mention that an insecticide developed with essentialoils does not need to be restricted to just one essential oil or evenessential oils only. It may be possible to combine patchouli and thymeoils with lower cost essential oils which showed moderate toxicity, forinstance, peppermint or clove oils. Alternately, essential oils could beadded to other insecticides such as pyrethrum based insecticides, toenhance their toxicity. The concept of synergism appears to be moremeaningful for reducing the dose of applied substances and the risk ofdeveloping resistance. It is important to note that negative synergismcan occur between EOs or their components and the other ingredientspresent in the total formulation. For more info about synergisticphenomena of EOs, see Bakkali et al. (2008), Nerio et al. (2010) andKhater (2011,2012).


SAFETY AND ADVANTAGES

Some of the purified terpenoid ingredients of EOs are moderately toxicto mammals. With few exceptions, the oils themselves or products basedon them are mostly nontoxic to mammals, birds, and fish ((Stroh et al.,1998: Isman, 2000). Many of the commercial products that include EOsare on the ‘Generally Recognized as Safe’ (GRAS) list fully approved bythe Food and Drug Administration (FDA) and Environmental ProtectionAgency (EPA) in USA for food and beverage consumption.

Eugenol is completely broken down to common organic acids by soil-borne Pseudomonas bacteria (Rabenhorst, 1996). Some EO constituentsacquired through the diet are actually beneficial to human health;consequently, there is no concern for residues of EO pesticides on foodcrops (Huang et al., 1994).

As broad-spectrum insecticides, both pollinators and natural enemiesare vulnerable to poisoning via direct contact by products based on EOs.Because of their volatility, EOs have limited persistence under fieldconditions; consequently, predators and parasitoids reinvade a treatedcrop one or more days after treatment and they are unlikely to be poisonedby residue contact as often occurs with conventional insecticides.

Farmers in developing countries, especially in tropical andsubtropical regions, get the benefits of botanical insecticides. Mosquitomanagement/abatement, is done through large-scale urban fogging, orfor individual property ‘‘perimeter’’ treatments, using controlled-releasetimers (‘‘puffers’’). Treatment of waterways and standing water usingessential oil as larvicides and repellents has been a very recent field ofinvestigation. They are used for home and garden use for flying andcrawling insects and related pests; management of turfgrass andlandscape pests; for ectoparasite control on dogs and cats; and aspersonal repellents for application to the skin and/or clothing to prevent/limit attack by blood-feeding flies and ticks.

The cytotoxic capacity of the essential oils, based on a prooxidantactivity, can make them outstanding antiseptic and antimicrobial agentsfor personal uses, i.e. for purifying air, personal hygiene, or even internaluse via oral consumption, and for insecticidal use for the preservationof crops or food stocks. Moreover, EOs are usually devoid of long-termgenotoxic risks and some of them show a very clear antimutageniccapacity which could be linked to an anticarcinogenic activity. Theprooxidant activity of essential oils or some of their constituents, likethat of some polyphenols, is capable in reducing local tumor volume ortumor cell proliferation by apoptotic and/or necrotic effects (Buhagiar


et al., 1999; Salim & Fukushima, 2003; Manosroi et al., 2006). Due tothe capacity of EOs to interfere with mitochondrial functions, they mayadd prooxidant effects and thus become genuine antitumor agents. Thepreviously mentioned safety and advantages designate that EOs couldfind their way from the traditional into the modern medical andinsecticidal domain. For more particulars about safety and advantagesof EOs, see Isman (2000, 2006, 2008, 2010), Tripathi et al. (2009), Nerioet al. (2010), Isman et al. (2011), Khater (2011, 2012) and Regnault-Roger et al. (2012).

COMMERCIALIZAION

The most important aspect of using EOs and/or their constituents istheir favorable mammalian toxicity and the relatively low cost of theactive ingredients, a result of their extensive worldwide use asfragrances and flavoring. In contrary, pyrethrum and neem are usedpredominantly for insecticide production. For valuable informationabout neem as source of bioinsecticides, see Ahmed et al. (1984) Forimet al. (2011) and Nicoletti et al. (2011).

Owing to their safety, EO based products are generally exemptedfrom toxicity data requirements by the Environmental ProtectionAgency (EPA), USA and some American companies have been able toproduce essentialoil-based pesticides to market. With over a dozenregistered products by the end of 1999, EcoSMART Technologies, Inc.,United States) is aiming to become a world leader in EO-basedpesticides. Such company currently produce aerosol and dustformulations containing proprietary mixtures of EO compounds,including eugenol and 2-phenethyl propionate for controlling domesticpests (cockroaches, ants, fleas, flies, wasps, etc.). These are marketedto pest control professionals under the brand name EcoPCOR, with lessconcentrated formulations for sale to the consumer under the nameBioganicTM.

EcoSMART Technologies also produce several products, such asMosquito & Tick Control which kills and repels mosquitoes, ticks, fleas,gnats, crickets, millipedes, mites and other crawling and flying insectsand the product holds eugenol, peppermint, rosemary, thyme andsesame oils; Flying Insect Killer which kills flies, gnats, mosquitoes,moths, wasps and other flying insect pests on contact and includespeppermint, cinnamon, sesame, wintergreen and canola oils; Bed BugKiller and Repellent contains peppermint, rosemary, wintergreen oiland white mineral oils; Home Pest Control which kills and repels over100 home invading pests, such as ants, beetles, centipedes, cockroaches,


crickets, earwigs, fleas, millipedes, pantry pests, pillbugs, silverfish,spiders, sowbugs, ticks and other crawling insect pests; and GardenInsect Killer for many common insect garden pests including aphids,mites, thrips, whiteflies, beetles, and caterpillars. The latest twoproducts contain peppermint, rosemary, thyme, and clove oils.

Mycotech Corporation produces CinnamiteTM, an aphidicide/miticide/fungicide for glasshouse and horticultural crops and ValeroTM,a miticide/ fungicide for use in grapes, berry crops, citrus and nuts.Both products are based on cinnamon oil, with cinnamaldehyde (30%in EC formulations) as the active ingredient.

Many commercial products such as Buzz Away (containing oils ofcitronella, cedarwood, eucalyptus and lemongrass), Green Ban(containing oils of citronella, cajuput, lavender, safrole from sassafrass,peppermint and bergaptene from bergamot oil) and Sin-So-SoftR(containing various oils) are in use as insect repellents (Chou et al.,1997). Several EO constituents are already in use as an alternative toconventional insecticides. For example, pulegone and citronellal areused as mosquito repellents.

A patented natural repellent is based on nepetalactone anddihydronepetalactone obtained from Nepeta cataria (N. cataria) that iseffective against cockroaches, mosquitoes, mites, ticks and otherhousehold insects (Scialdone, 2006; Hallahan, 2007). Nootkatone fromvetiver oil and its derivatives, tetrahydronootkatone and 1,10-dihydronootkatone have been patented as repellent against mosquitoes,cockroaches, termites, and ants (Henderson et al., 2005 a,b: Zhu et al.,2005). For more information about patent literature on mosquitorepellent inventions which contain plant essential oils, see Pohlit et al.,(2011).

Several smaller companies in the U.S. and the U.K. have developedgarlic-oil based pest control products. There are consumer insecticidesfor home and garden, in U.S.A, using mint oil as the active ingredient.Menthol has been approved for use in North America for control oftracheal mites in beehives. A product produced in Italy (Apilife VARTM)containing thymol and lesser amounts of cineole, menthol and camphoris used to control varroa mites in honeybees (Canadian Honey Council;http://www.saskatchewanbeekeepers.ca/users/folder.asp@FolderID=5317.htm).

Neem is widely used as insecticide and repellent. The biologicalcompound MiteStop® based on a neem seed extract has a very high andbroad efficacy against a wide spectrum of insects, ticks and mites that


molest birds, animals and humans (Abdel-Ghaffar et al., 2008a, b; Abdel-Ghaffar & Semmler, 2007; Abdel-Ghaffar et al., 2009; Locher et al.,2010a; b). More products based on neem and other botanical resourceswill be discussed later on in this chapter.

See Khater (2012) for more information in relation to resourceavailability, production and barriers to commercialization of botanicals.

Standardization

The chemical profile of the essential oil products differs not only in thenumber of molecules but also in the stereo chemical types of moleculesextracted, according to the type of extraction, which chosen accordingto the purpose of the use. The extracted product can vary in quantity,quality, and in composition according to plant organ, age, vegetativecycle stage, climate, and soil composition (Masotti et al., 2003; Angioniet al., 2006). As with many herbal products, herbal repellents have aproblem of standardization. For example, the oil obtained from Cy.nardus, which is used against mosquitoes, has a considerably morelasting effect than the oil from Cymbopogon commutatus, Cymbopogonmartinii or Cymbopogon pendulus (Tyagi et al., 1998).

In order to obtain essential oils of constant composition, they haveto be extracted under the same conditions from the same organ of theplant which has been growing on the same soil, under the same climateand has been picked in the same season. Most of the commercializedessential oils are chemotyped by gas chromatography and massspectrometry analysis published (European pharmacopoeia, ISO, WHO,Council of Europe) to ensure good quality of essential oils. For moreinformation about standardization, regulatory approval andcommercialization, see Tripathi et al. (2009), Isman (2006, 2010), Dubeyet al. (2011), and Khater (2012).

IMPROVING THE EFFICACY

EOs are good penetrants which increase their own bioavailability and thatof coadministered products. These properties are related to the disruptionof lipid bilayers in cells. Coconut oils, which have some repellent effectthemselves, are used for preference as carriers, particularly for neem,Azadirachta indica (Az. indica) oil (e.g. Sharma et al., 1993).

Some EOs have specific modes of action that make them goodsynergists. In particular, a number of compounds are well-establishedinhibitors of insect P450 cytochromes responsible for phase I metabolism


of xenobiotics, including insecticides. These include phytochemicalscontaining methylene dioxy rings such as dillapiole in dill (Anthemasowa, Ant. sowa) oil, piperamides from Piper spp. oils, andfuranocoumarins from oil of bergamot (Citrus bergamia). Dillapiole andsemisynthetic derivatives have a synergistic factor of two- to six foldwhen combined with botanical insecticides (Belzile et al., 2000), butpiperamides have a remarkable synergism factor of 11 when combinedwith pyrethrin (Jensen et al., 2006) and they have profound effects onthe cytochrome P450 transcriptome of treated insects.

It worth to mention that some oils are mosquito repellents such ascoconut, palm nut and andiroba oils, although all of these three oils arefar less effective than DEET, they may be useful as carriers for otherrepellent actives as they are cheap and contain unsaturated fatty acidsand emulsifiers that improve repellent coverage and slow evaporationof volatile repellent molecules (see Maia & Moore (2011) and Khater(2011, 2012) for more details).

Attractant adhesive films with EOs are used for controlling insectsin agriculture and horticulture (Klerk’s Plastic Industries B.V., 1990).EOs can also be incorporated with polymers into sheets. The stabilityof essential oil formulations can also be influenced by the use of specificagents known to maintain essential oil stability or by using techniquessuch as microencapsulation or nanoencapsulation during themanufacturing process. Smart delivery systems will allow real-timemonitoring and regulation of delivery of constituents (nutraceuticals,nutrients, drug, insecticides, pesticides, fertilizers, vaccines, etc.) topeople, animals, plants, insects, microorganisms, soils and theenvironment.

MICROENCAPSULATION

Encapsulation reduces the loss of the active agents and offers thepossibility of a controlled release of oil vapors. Therefore, it is a suitabletechnology for the formulation of EO- based pesticides. Encapsulatedproduct from Syngenta, one of the world’s largest agrochemicalcorporations, delivers a broad control spectrum on primary andsecondary insect pests of cotton, rice, peanuts, and soybeans. Marketedunder the name Karate® ZEON, a quick release microencapsulatedproduct contains the active compound lambda-cyhalothrin (a syntheticinsecticide based on the structure of natural pyrethrins) which breaksopen on contact with leaves. The encapsulated product “gutbuster” onlybreaks open to release its contents when it comes into contact withalkaline environments, such as the stomach of certain insects.


Microcapsules containing the most promising oils such asRs. officinalis and Thymus herba-barona induce larvicidal effects againstgypsy moth, Limantria dispar, larvae, one of the most serious pests ofcork oak forests. The microcapsules had toxic effects at a concentrationsimilar to that usually employed for localized treatments withmicrogranular synthetic pesticides. Toxicity appeared to be maximizedwhen the microparticles adhered to the typical hair structures of severaldefoliator families (Moretti et al., 2002). See Nerio et al. (2010), Khater(2012), and Regnault-Roger et al. (2012) for more innovative ideas aboutimproving the efficacy of EOs.

NANOTECHNOLOGY

The potential uses of nanotechnology are immeasurable. These includeenhancement involving nanocapsules for vector and pest managementand nanosensors for pest detection. Nanoparticles are 1-100 nm indiameter. Such particles are agglomerated atom by atom.Nanotechnology is used widely in Agriculture and Food (Joseph &Morrison, 2006). Such technology improves pesticide delivery systemswhich can take action to environmental changes in a controlled mannerin response to different signals e.g. heat, moisture, ultrasound, magneticfields, etc. Nanosilica, a novel nanobiopesticide, surface chargedmodified hydrophobic nanosilica (~3-5 nm) could be successfully usedto control a range of agricultural insect pests and animal ectoparasitesof veterinary importance (Ulrichs et al., 2005, 2006 a, b, c, d, e).

Using oil-in-water microemulsions as a nano-pesticide deliverysystem to replace the traditional emulsifiable concentrates (oil), in orderto reduce the dosage of pesticides and the use of organic solvent andincrease the disparity, wettability and penetration properties of thedroplets is being developed. These microemulsions would be a usefulstrategy in green pesticide technology.

Green synthesis of nanoparticles (NPs), such as silver or gold NPs,has been attracting increasing attention in recent years. The pediculicideand larvicidal activity of synthesized Ag NPs using an aqueous leafextract of Tinospora cordifolia (sizes measuring 54–80 nm) showedmaximum mortality against the human head louse, Pediculus humanuscapitis (P.h. capitis) and fourth instar larvae of Anopheles subpictus(An. subpictus) and Culex quinquefasciatus (Cx. quinquefasciatus) (themedin lethal concetraion, LC50 = 12.46, 6.43 and 6.96 mg l”1),respectively (Jayaseelan et al., 2011). The methanol, aqueous leafextracts and synthesized Ag NPs of Euphorbia prostrata (E. prostrate)possessed high acaricidal activity against the adult cattle tick,


Haemaphysalis bispinosa (Hm. bispinosa) and the haematophagous fly,Hippobosca maculata (Hip. maculata) infesting cattle in India (Zahir& Rahuman, 2012).

The first report on the activity of synthesized Ag NPs using leafaqueous extract of Manilkara zapota (Mn. zapota) against the housefly,Musca domestica (Mu. domestica) had been provided by Kamaraj et al.(2012). Adult flies were exposed to different concentrations of theaqueous extract of synthesized Ag NPs, 1 mM silver nitrate (AgNO3)solution and aqueous extract of Mn. zapota. AgNPs showed 72%mortality in 1 h, 89% mortality was found in 2 h, and 100% mortalitywas found in 3 h exposure at the concentration of 10 mg/mL; whereas,the leaf aqueous extract showed 32% mortality in 1 h, 48% mortalitywas found in 2 h, and 83% mortality was found in 3 h exposure atconcentration of 50 mg/mL. The most efficient activity was observed insynthesized Ag NPs against Mu. domestica (LD50 = 3.64 mg/mL; LD90 =7.74 mg/mL), the moderate activity reported in the aqueous extract ofMn. zapota (LD50 = 28.35 mg/mL; LD90 = 89.19 mg/mL) and nil activitywere observed in AgNO3 solution at 3 h exposure time at 10 mg/mL.

The acaricidal and larvicidal activity of synthesized silvernanoparticles (AgNPs) utilizing aqueous leaf extract from Musaparadisiaca L (Ms. paradisiaca). were evaluated against the larvae ofHm. bispinosa and larvae of hematophagous fly Hip. maculata andagainst the fourth-instar larvae of malaria vector, Anopheles stephensi(An. stephensi) Liston, Japanese encephalitis vector, Culextritaeniorhynchus (Cx. tritaeniorhynchus). The parasite larvae wereexposed to varying concentrations of aqueous extract of Ms. paradisiacaand synthesized AgNPs for 24 h. The maximum efficacy was observedin the aqueous extract of Ms. paradisiaca against Hm. bispinosa, Hip.maculata, and the larvae of An. stephensi, Cx. tritaeniorhynchus withLC50 values of 28.96, 31.02, 26.32, and 20.10 mg/lm, respectively. Thesynthesized AgNPs of Ms. paradisiaca showed the LC50 against Hm.bispinosa, (1.87 mg/l), Hip. maculata (2.02 mg/l), and larvae of An.stephensi (1.39), against Cx. tritaeniorhynchus (1.63 mg/l), respectively(Jayaseelan et al., 2012).

Anti-parasitic activities of synthesized zinc oxide nanoparticles (ZnONPs) against the larvae of cattle tick Rhipicephalus (Boophilus) microplus(R. microplus), P.h. capitis, larvae of malaria vector, An. subpictus, andfilariasis vector, Cx. quinquefasciatus were evaluated through exposureto filter paper envelopes impregnated with different ZnO NPconcentrations. The mortality effects of synthesized ZnO NPs were 43%at 1 h, 64% at 3 h, 78% at 6 h, and 100% after 12 h against R. microplus


activity. In pediculocidal activity, the results showed that the optimaltimes for measuring mortality effects of synthesized ZnO NPs were 38%at 10 min, 71% at 30 min, 83% at 1 h, and 100% after 6 h against P.h.capitis. One hundred percent lice mortality was observed at 10 mg/Ltreated for 6 h. The mortality was confirmed after 24 h of observationperiod. The larval mortality effects of synthesized ZnO NPs were 37%,72%, 100% and 43%, 78% and 100% at 6, 12, and 24 h against An.subpictus and Cx. quinquefasciatus, respectively. The maximum efficacywas observed in zinc oxide against R. microplus, P.h. capitis, and thelarvae of An. subpictus, Cx. quinquefasciatus with LC50 values of 29.14,11.80, 11.14, and 12.39 mg/L, respectively. The synthesized ZnO NPsshowed the LC50 against R. microplus (13.41 mg/L), P.h. capitis(11.80 mg/L), and the larvae of An. subpictus (0.945 mg/L), againstCx. quinquefasciatus (4.87 mg/L), respectively ( Kirthi et al., 2011).

Synthesized silver nanoparticles Ag NPs using leaf aqueous extractof Lawsonia inermis possess excellent anti-lousicidal activity against thehuman head louse, P.h. capitis, and sheep- biting louse, Bovicola ovis (B.ovis) through direct contact method. The average percent mortality forsynthesized Ag NPs was 33, 84, 91, and 100 at 10, 15, 20, and 35 min,respectively against B. ovis. The maximum activity was observed in theaqueous leaf extract of L. inermis, 1 mM AgNO3 solution, and synthesizedAg NPs against P.h. capitis with LC50 values of 18.26, 7.77, and 1.33 mg l-

1, respectively, and against B. ovis showed with LC50 values of 21.19,8.49, and 1.41 mg l-, respectively (Marimuthu et al., 2011).

Zahir et al. (2012) evaluated the efficacies of aqueous leave extracts ofE. prostrata, silver nitrate (AgNO3) solution (1mM) and silvernanoparticles, synthesized Ag NPs against the adult of Sitophilus oryzaeL (S. oryzae). The LD50 values were 213.32, 247.90, 44.69 mg/kg –1;LD90=1648.08, 2675.13, 168.28 mg/kg –1, respectively, which indicatethat the leave aqueous extracts of E. prostrata, and synthesized Ag NPshave the potential to be used as an ideal eco-friendly approach for thecontrol of the S. oryzae. Nanoparticles loaded with garlic essential oilare efficacious against the red flour beetle, Tribolium castaneum (T.castaneum) Herbst (Yang et al., 2009). Aluminosilicate filled nanotubecan stick to plant surfaces while nano ingredients of nanotube have theability to stick to the surface hair of insect pests and ultimately entersthe body and influences certain physiological functions (Patil, 2009).

DNA tagged gold nanoparticles are effective against the majorpolyphagous pest, Spodoptera litura (S. litura), 2nd instar larvae. TheLC50 (216.91 to 938.95 conc. at 95% CI) increased as the larval ageincreased (Chakravarthy et al., 2012). Encapsulated citronella oil


nanoemulsion is prepared by high-pressure homogenization of 2.5%surfactant and 100% glycerol, to create stable droplets that increasethe retention of the oil and slow down release. The release rate relateswell to the protection time so that a decrease in release rate can prolongmosquito protection time (Sakulku et al., 2009).

Innovative alternative approach had been conducted to control thehematophagous fly and sheep-biting louse by synthesized titanium dioxidenanoparticles (TiO2 NPs) utilizing leaf aqueous extract of Catharanthusroseus (C. roseus) against the adults of hematophagous fly, Hip. maculata,and B. ovis. Adulticidal parasitic activity was observed in varyingconcentrations of aqueous leaf extract of C. roseus, TiO2 solution, andsynthesized TiO2 NPs for 24 h. The maximum parasitic activity wasobserved in aqueous crude leaf extracts of C. roseus against the adults ofHip. maculata and B. ovis with LD50 values of 36.17 and 30.35 mg/L,respectively. The highest efficacy was reported in 5 mM TiO2 solutionagainst Hip. maculata and B. ovis (LD50 = 33.40 and 34.74 mg/L),respectively, and the maximum activity was observed in the synthesizedTiO2 NPs against Hip. maculata and B. ovis with LD50 values of LD50 =7.09 and 6.56 mg/L, respectively (Velayutham et al., 2012).

Likewise, nanoencapsulation of garlic oil using polyethylene glycolcoated nanoparticles dramatically improved the stability of garlic oilin the control of the stored product pest, T. castaneum. Thenanoencapuslated garlic oil was 80% as toxic at 5 months as the firstday, while non-encapusalted garlic oil caused only 11% toxicity. Inaddition, the chemical composition of the nanoencapsulated garlic oilwas still similar to the original composition, even after 5 months hadpassed (Yang et al., 2009).

Nanoparticles are simple, non-toxic, ecofriendly green material andwidely acceptable publicly. For more in rank about usages ofnanoparticles, see Torney (2009), Omara et al. (2009), Yang et al. (2009),Bhattacharyya et al. (2008, 2010), Ahmed et al. (2011), Hashim (2011),and Khater (2011, 2012).

ESSENTIAL OILS FOR CONTROLLING SERIOUS PESTS

Insects of Medical and Veterinary Importance

Mosquitoes

Mosquitoes are one of the most important insect pests that affect thehealth and well being of humans and domestic animals worldwide.Female mosquitoes require a blood meal for egg production, and they


produce a painful bite as they feed. They act as vectors for many tropicaland subtropical diseases such as dengue fever, yellow fever, malaria,filariasis and encephalitis of different types. Mosquito control is animportant component in the strategies to manage mosquito-bornediseases. In the past few years, several authors have investigatedvarious plant compounds with anti-mosquito potential that includedlarvicidal, adulticidal and repellent activities.

Culex species

Some Egyptian essential oils provided an excellent potential forcontrolling Culex pipiens (Cx. pipiens). The LC50 values were 32.42,47.17, 71.37, 83.36, 86.06, and 152.94 ppm for fenugreek (Trigonellafoenum-grecum), earth almond (Cyperus esculentus), mustard (Brassicacompestris), olibanum (Boswellia serrata), rocket (Eruca sativa), andparsley (Carum ptroselinum), respectively. The tested oils altered somebiological aspects of Cx. pipiens, for instance, developmental periods,pupation rates, and adult emergences. The lowest concentrations ofolibanum and fenugreek oils (7.81 ppm for both oils) causedremarkable prolongation of larval (14.90 and 9.75 days, respectively)and pupal (8.25 and 5.85 days, respectively) durations. Data alsoshowed that the increase of concentrations was directly proportionalto reduction in pupation rates and adult emergences. Remarkablereduction in pupation rate (1.67 %) was achieved by mustard oil at1000 ppm. Adult emergence was suppressed by earth almond andfenugreek oils at 125 ppm. In addition, the tested plant oils exhibitedvarious morphological abnormalities on larvae, pupae, and adults.Consequently, fenugreek was the most potent oil and the major causeof malformation of both larval and pupal stages (Khater & Shalaby,2008).

Ginger, Zingiber officinale (Zn. officinale), yield volatile oil rangesfrom 1 to 3% which contains mainly mono and sesquiterpenoids (Ali etal., 2008). The essential oil was found to have larvicidal activity againstthe late insetars of the filarial mosquito Cx. quinquefasciatus with LC50

of 50.78 ppm after 24 h of treatment (Pushpanathan et al., 2008). Thehydrolates of four plants, Zanthoxylum limonella (Z. limonella), Zn.officinale, Curcuma longa (Cr. longa), and Cymbopogon citratus (Cy.citratus) induced larvicidal activity against laboratory reared Cx.quinquefasciatus. Z. limonella was the most effective hydrolate ofagainst Cx. quinquefasciatus with LC50 15.5 (%v/v). The larvicidalactivity of hydrolates of Zn. officinale, Cr. longa and Cy. citratus werealso found promising with LC50 of 21.8, 35.5 and 38.8 (%v/v) (Rabha etal., 2012).


An insecticide containing azadirachtin form neem (Az. indica) extractwas effective against larvae and pupae of Cx. pipiens. After treatmentof larval stage, LC50 and LC90 values for azadirachtin were 0.35 and1.28 mg/L in direct effect and 0.3-0.99 mg/l in indirect effect, respectively.Second, after treatment of the pupal stage, the LC50 and LC90 in directeffect were measured as 0.42 -1.24mg/l and in indirect effect was0.39mg/l-1.14mg/l, respectively. Mosquito adult fecundity was markedlydecreased and sterility was increased by the azadirachtin aftertreatment of the fourth instar and pupal stage. The treatment alsoprolonged the duration of the larval stage (Alouani et al., 2009). It worthto mention that rosemary controlled Cx. pipines effectively (Shalaby &Khater, 2005).

The essential oils of spices/aromatic medicinal plants particularlyFoeniculum vulgare and Tagetes patula carry huge potential as amosquito larvicide (Rana & Rana, 2012). Moreover, EOs of Cy. citratusinduced larvicidal effect against Cx. quinquefasciatus. The LC50 valuescalculated after 24 hours treatment for the 2nd, 3rd and 4th larval instar

Fig. 3: . Morphological abnormalities induced by some essential oils againstmosquitoes treated as 4th larval instars. A. Normal larva. B-D.Malformed larvae. B. Larvae with deformed cuticles. C. Larva withan opaque swelling on the thorax and black coloration at the posteriorend. D. Pharate pupa. E. Normal Pupa. F, G. Elephantoid pupa,with enlarged cephalic region and extended abdomen. H. Blackcephalothorax (lower arrows) and extended abdomen withtransparent posterior end (upper arrow) and no anal gills. I. Normaladult. J. flaiur of adult eclosion. K. malformed adult, deformed wingand legs. Adapted form Khater (2003)


were 144.54, 165.70 and 184.18 ppm, respectively (Pushpanathan etal., 2006). Sesame, Sesamum indicum, nigella, Nigella sativa, andonion, Allium cepa (Al. cepa), oils induced larvicidal effect andadversely affect pupation and adult emergence rates of Cx. pipiens,Fig. 3 (Khater, 2003). In addition, Ansari et al. (2000) found thatapplication of peppermint, Mentha piperita L. (M. piperita) oil at 3ml/m2 of water surface area resulted in 100% mortality within 24 hfor Cx. quinquefasciatus.

Anopheles species

It was proved by Ajaiyeoba et al. (2008) that essential rhizome oil fromCr. longa was most potent larvicide against the An. gambiae with anLC50 of 0.017 mg/ml. The plant-based compounds from neem oil such aslimonoids may be an effective alternative to conventional syntheticinsecticides for the control of An. stephensi (Senthil-Nathan et al., 2005)M. piperita oil at 3 ml/m2 of water surface area resulted in 85% for An.stephensi (Ansari et al., 2000). Alkaloids isolated from Annona squamosahave shown larvicidal growth-regulating and chemosterilant activitiesagainst An. stephensi at concentrations of 50 to 200 ppm (Saxena et al.,1993).

Four essential oil of basil accessions conferred complete mosquitorepellency against Anopheles mosquito (assayed by the human-baittechnique) lasting for 1.5 to 2.5 h per one application of 0.1 mL to avolunteer’s arm (Nour et al., 2009).

Aedes sepcies

The larvicidal activity of hydrodistillate extracts from peppermint, M.piperita, Ocimum basilicum L. (Oc. basilicum), Cr. longa L. and Zn.officinale L. had been proved against the dengue vector Ae. aegypti.The results indicated that the mortality rates at 80, 100, 200 and 400ppm of M. piperita, Zn. officinale, Cr. longa and Oc. basilicumconcentrations were highest amongst all of the crude extracts testedagainst all the larval instars and pupae of Ae. aegypti. LC90 values were47.54 and 86.54 ppm for M. piperita, 40.5 and 85.53 ppm for Zn.officinale, 115.6 and 193.3 ppm for Cr. longa and 148.5 and 325.7 ppmfor Oc. basilicum, respectively. All of the tested oils proved to havestrong larvicidal activity (doses from 5 to 350 ppm) against Ae. aegyptifourth instars, with the most potent oil being M. piperita extract,followed by Zn. officinale, Cr. longa and Oc. basilicum. In general, earlyinstars were more susceptible than the late instars and pupae (Kalaivaniet al., 2012).


The oil of Carapa guianensis (Ca. guianensis), extracted fromandiroba seed kernels, occurs not only in southern Central Americabut also in Colombia, Venezuela, Suriname, French Guiana, Brazil,Peru, Paraguay, and the Caribbean islands (Pennington et al., 1981).Studies demonstrating the larvicidal activity of Ca. guianensis werefirstly described by Silva et al. (2004) for wild populations of Aedesalbopictus (Ae. albopictus). After that, Mendonça et al. (2005) evaluatedthe oil of this plant for laboratory populations of Ae. aegypti. Oils of Ca.guianensis and Copaifera spp. are well known in the Amazonian regionas natural insect repellent. Both oils brought on larvicidal in wildpopulations of Ae. aegypti with a history of exposure to organophosphate.The wild populations of Ae. aegypti, transmitting the dengue virus inthe environment, were also susceptible to Ca. guianensis and Copaiferasp. oils. The lethal concentrations for Copaifera sp. ranged from LC50

47 to LC90 91 (milligrams per liter), and for Ca. guianensis, they wereLC50 136 to LC90 551 mg/L (Prophiro et al., 2012).

The essential oil of leaves of Hyptis martiusii Benth and 1,8-cineoleshowed pronounced insecticidal effect against Ae. aegypti larvae (Araújoet al., 2003). Essential oil from Eucalyptus globulus (Eu. globulus) istoxic to Ae. aegypti larvae and showed LC50 of 32.4 ppm (Lucia et al.,2007). The essential oils obtained from the inflorescence of Pipermarginatum, though proved to be effective larvicides, did not interferesignificantly in the oviposition activity of Ae. aegypti (Autran et al.,2009).

The hydrolates of four plants, Z. limonella, Zn. officinale, Cr. longa,and Cy. citratus induced larvicidal activity against laboratory rearedAe. albopictus .The hydrolate of Z. limonella was most effective againstboth Ae. albopictus with LC50 11 (%v/v). The larvicidal activity ofhydrolates of Zn. officinale, Cr. longa and Cy. citratus were also foundpromising with LC50 at 15.8, 24.7 and 33.7 (%v/v) respectively againstAe. albopictus (Rabha et al., 2012). M. piperita oil at 3 ml/m2 of watersurface area resulted in 90% for Ae. aegypti larvae (Ansari et al. 2000)and the essential oil of Cy. citratus was observed to have an LC50 of 69ppm (Cavalcanti et al., 2004).

Mosquito control and temperature variation

In relation to different temperature, the effectiveness of the oils on larvalmortality was directly related to the increase of temperature, and betterresults were observed for a temperature at 25°C (Prophiro et al., 2012).At temperatures under 25°C, the mortality decreased significantly.These results were expected, since mosquitoes decrease their movementsor even their metabolism when temperatures are lower or higher than


optimal. Therefore, the direct influence of low temperatures on larvalmortality of Ae. aegypti indicates the necessity of a larger quantity ofoil estimated for effective control. Likewise, Patil et al. (2011) evaluatedlarvicidal activity of extracts of medicinal plants Plumbago zeylanicaL. and Cestrum nocturnum L. against Ae. aegypti; the LC50 values ofboth plants were less than 50 ppm. The larvicidal stability of the extractsat five constant temperatures (19°C, 22°C, 25°C, 28°C and 31°C)evaluated against fourth instar larvae revealed that toxicity of bothplant extracts increases with increase in temperature.

Eggs and larval stages are the weakest link in mosquito life cycleand effective mosquito control must include successful ovicidal andlarvicidal programs. The larvicidal mode of action of essential oils couldbe explained as the susceptibility of mosquito larvae and pupae tosurface materials entering their tracheal system, observing thatessential oils increased the tendency to tracheal flooding and chemicaltoxicity (Corbet et al., 1995).

Mosquito repellents

The World Health Organization also recommends repellents forprotection against malaria, because of the increasing resistance ofPlasmodium falciparum to anti-malarial drugs such as chloroquine(Anonymous, 1988). Several reports are available about the repellentproperties of essential oils against adult mosquitoes. Botanical, herbalor natural-based repellents include one or several plant essential oils.These oils are considered safe by the EPA at the low concentrationsused, but provide a limited duration of protection against mosquitoes(< 3 hours). Citronella is the principal and sometimes only activeingredient in many plant-based insect repellents. (See Stafford (2007)for more details).

Regarding the use of eucalyptus, burning of leaves of Eucalyptuscitriodora (Eu. citriodora) provides a cost-effective method of householdprotection against mosquitoes in Africa (Seyoum et al., 2003). A varietyof eucalyptus oils are reported to be very good repellents to mosquitoes,but they are attractive to other biting flies. Eucalyptus oil has beenused as an antifeedant, particularly against biting insects as eucalyptusbased products used on humans as insect repellent can protect frombiting insects up to 8 h depending upon the concentration of the essentialoil (Trigg, 1996a,b). Moreover, the insect-repellent activity could beextended up to 8-days, when eucalyptus essential oils are applied onthe clothes (Mumcuoglu et al., 1996). Eucalyptus oil (30%) can preventmosquito bite for 2 h; however, the oil must have at least 70% cineolecontent (Fradin & Day, 2002).


Recently, a plant derived repellent, para-methane 3–8, diol (PMD)naturally found in the oil of the lemon eucalyptus plant. The compoundwas isolated from waste distillate of lemon eucalyptus oil extract, butthe synthetic compound was used. PMD is the only plant-based repellentthat has been encouraged for use in disease endemic areas by the CDC(Centres for Disease Control). It has been proven to be suitablyefficacious and safe to compete with DEET in the field of diseaseprevention, and repellents have been recognized by WHO as a usefuldisease prevention tool to complement insecticide based means of vectorcontrol. It is safe for both children and adults as its the toxicity of PMDis very low. However, the label indicates it should not be used on childrenunder the age of three (A 2% soybean oil-based repellent has beenreported to provide an average of 1.5 hours of protection againstmosquito bites, while other botanical repellents tested provided onlyshort-term protection with a mean protection time of only 3 to 20minutes. (See Stafford (2007); Khater (2012) for more particulars).

Oil of lemon eucalyptus, soybean oil or geraniol is the sole activeingredients in some products. Available in several brands orformulations, oil of lemon eucalyptus provides protection againstmosquitoes similar to low concentrations of DEET. Two productscontaining oil of eucalyptus or its primary compound provided the mostprotection against mosquitoes with protection ranging from 60 to 217minutes, better than 7-15% DEET. Other essential oils used in natural-product based repellents include peppermint, lemongrass, lavender,cedar, canola, rosemary, pennyroyal, geranium and cajeput, see Stafford(2007).

The oil of lemon eucalyptus or PMD were listed as active ingredientsin only four products of 88 U.S. products examined by Arnason et al.(2011). Inappropriately, many of these products suffer from a shortperiod of efficacy compared to DEET, because they are volatile or quicklyabsorbed and are lost from the skin surface. An exception is catnip EO,which contains the highly oxygenated compound, nepetalactone. Suchcompound is heavier than water and has an efficacy up to 4 h againstAedes sp., when properly formulated, compared to 6 h for DEET. Eventhough catnip oils are attractive to some species of felines, the attractionof domesticated cats has not been a problem so far. See Regnault-Rogeret al. (2012) for more details.

Oil of lemon eucalyptus, soybean oil or geraniol is the sole activeingredients in some products. Available in several brands orformulations, oil of lemon eucalyptus provides protection againstmosquitoes similar to low concentrations of DEET. Two products


containing oil of eucalyptus or its primary compound provided the mostprotection against mosquitoes with protection ranging from 60 to 217minutes, better than 7-15% DEET. Other essential oils used in natural-product based repellents include peppermint, lemongrass, lavender,cedar, canola, rosemary, pennyroyal, geranium, and cajeput amongothers (see Stafford (2007).

Concerning geraniol, it is effective in repelling mosquitoes (Omoloet al., 2004). Therefore, geraniol-based products are availablecommercially as natural repellents. Geraniol candles were found to bemore effective than citronella and linalool candles in protecting a personfrom being bitten indoors by mosquitoes and sand flies (Müller et al.,2008). In a comparative study between three botanical naturalrepellents, a lemongrass extract in combination with 25% geraniol oilexhibited the longest protection time against mosquitoes (Qualls & Xue,2009). Müller et al. (2009) determined the degree of personal protectionprovided by commercial citronella, linalool and geraniol candles ordiffusers. Indoors, the repellency rate of geraniol candles was 50%, whilethe diffusers provided a repellency rate of 97%. Outdoors, geranioldiffusers placed 6 m from mosquito traps repelled female mosquitoesby 75%. Geraniol had significantly more repellent activity thancitronella or linalool in both indoor and outdoor settings. Geraniol alsoaffected the activation and orientation stages of the blood-feedingbehavior; after 48 h of exposure to 0.250 µg/ml geraniol, almost 100%of Ae. albopictus lost their host-seeking ability (Hao et al., 2008).

Oils of soybean, lemongrass, cinnamon and PMD (from lemoneucalyptus), citronellal (from lemongrass) and 2-phenethylpropionate(from groundnut), are effective against mosquitoes based on short-termtests with humans, although their duration is a very controversial issue(Fradin & Day, 2002).

Essential oils of six plants growing in Kenya proved repellentactivities against An. gambiae sensu stricto. The oils of Conyza newiiand Plectranthus marrubioides were the most repellent (RD50 = 8.9 × 10"5

mg cm”2, 95% CI) followed by Lippia javanica, Lippia ukambensis,Tetradenia riparia, Iboza multiflora and Tarchonanthus camphoratus.Eight constituents of the different oils (perillyl alcohol, cis-verbenol,cis-carveol, geraniol, citronellal, perillaldehyde, caryophyllene oxide anda sesquiterpene alcohol) exhibited relatively high repellency. Foursynthetic blends of the major components (present in ~*1.5%) of theessential oils were found to exhibit comparable repellent activity to theparent oils (Omolo et al., 2004).


MiteStop®, based on a neem seed extract, had a considerable repellenteffect on bloodsucking, mosquitoes, tabanids, ceratopogonids, simuliids,as well as on licking flies. This repellency effect was noted to last for upto 7 days if the horses were not washed (Al-Quraishy et al., 2012a).

Against An. stephensi, the repellency of botanical repellents waslower than that of DEET as a synthetic repellent. The protection timeof 50% essential oils of marigold (Calendula officinalis) and myrtle,(Myrtus communis) were respectively 2.15 and 4.36 hours compared to6.23 hours for DEET 25%. The median effective dose (ED50) of 50%essential oils was 0.1105 and 0.6034 mg/cm2, respectively, in myrtleand marigold. The figure for DEET was 0.0023 mg/cm2 (Tavassoli etal., 2011).

Skin repellent test at 1.0, 2.5 and 5.0 mg/cm2 concentration of Cy.citratus gave 100% protection against Cx. quinquefasciatus up to 3.00,4.00 and 5.00 hours, respectively. The total percentage of protection ofthis essential oil was 49.64% at 1.0 mg/cm2, 62.19% at 2.5 mg/cm2 and74.03% at 5.0 mg/cm2 for 12 hours (Pushpanathan et al., 2006)..

The use of the essential oils of Oc. basilicum as promising new naturalrepellents at 0.1% concentration against the Anopheles and Aedesmosquitoes has been suggested by Nour et al. (2009). The five most effectiveoils which induced 100% repellency against An. aegypti, An. stephensi,and Cx. quinquefasciatus were those of litsea, Litsea cubeba (Lt. cubeba),cajeput (Melaleuca leucadendron), niaouli (Melaleuca quinquenervia), violet(Viola odorata), and catnip (N. cataria) (Amer & Mehlhorn, 2006).

The repellency of Zanthoxylum armatum seed oil (ZA-SO), alone orin combination with vanillin (VA), its six major constituents, and anotherfour major previously known Zanthoxylum piperitum fruit oilconstituents, as well as aerosol products containing 5 or 10% ZA-SOand 5% VA, was proved against female Ae. aegypti in laboratory andfield studies (Kwon et al., 2011).

The essential oil of catmint, N. cataria, was hydrogenated to yieldan oil enriched in dihydronepetalactone (DHN) diastereomers. Thismaterial was used for the preparation of liquid alcohol–based and lotionformulations. The efficacy of these formulations as repellents was testedafter application to human test subjects at two locations in the UnitedStates: Maine and Florida. In Maine, data on repellency of thehydrogenated catmint oil formulations toward black flies (Simuliumdecorum Walker) and mosquitoes (primarily Aedes intrudens Dyar) wereobtained. In these tests, protection from black flies was conferred for 6


h or more with all formulations, and both liquid and lotion formulationsat 15 wt% active ingredient gave complete protection for 7.5 h. Allformulations conferred protection from mosquitoes for >4 h, with thebest (15 wt% lotion) giving >8 h of complete protection. In Florida, dataon repellency toward a mixed population of mosquitoes indicated thatall formulations conferred protection for >4 h, with the 15 wt% lotiongiving >6 h complete protection from bites (Spero et al., 2008).

Oviposition deterrence and ovicidal potential

The mosquito oviposition behavior has been investigated as one of theprospective parameters for their control improved (Bassolé et al., 2003).Some essential oils, peppermint oil (M. piperita), basil oil (Oc. basilicum),rosemary oil (Rs. officinalis), citronella oil (Cy. nardus) and celery seedoil (Apium graveolens, Ap. graveolens), induce oviposition deterrenceand ovicidal potential against female adults of Ae. Aegypti (Warikoo etal., 2011).

Oils of Cinnamomum zeylanicum (Cn. zeylanicum), Zn. officinale,and Rs.officinalis expressed oviposition deterrent, ovicidal, and repellentactivities against An. stephensi, Ae. aegypti, and Cx. quinquefasciatus(Prajapati et al., 2005). Similar oviposition deterrent potential of theEO of Cn. zeylanicum against the previously mentioned three mosquitospp. has been reported (Prajapati et al., 2005). Likewise, relative highoviposition deterrence of the essential oils obtained from Cr. longa(94.7%), Schefflera leucantha (91.6%), Zn. officinale (90.1%), Vitextrifolia (89.1%), Melaleuca cajuputi (87.9%), Hedychium coronarium(87.5%), Psidium guajava (87.1%), Manglietia garrettii (86.1%), andHouttuynia cordata (85%) against Ae. aegypti. Furthermore, theessential oils of Pip nigrum (82%), Lt. cubeba (80.6%), andEleutherococcus trifoliatus (80.2%) exhibited moderate degrees ofdeterrence (Tawatsin et al., 2006).

The EOs of three plants, Cymbopogon proximus, Lippia multiflora,and Ocimum canum (Oc. canum) have ovicidal activity against Ae.aegypti and An. gambiae. The ovicidal potential of all the oils againstthese mosquitoes, the essential oil from Oc. canum being the leasteffective among the three (Bassolé et al., 2003). Cy. citratus oil at 300ppm induced 100% ovicidal activity against Cx. quinquefasciatus(Pushpanathan et al., 2006).

Mosquitoes can sense and detect various chemical signals by sensoryreceptors present on their antennae and select or reject their specificoviposition sites. Mosquito oviposition behavior could allow the


formulation of effective oviposition deterrents for the reduction ofmosquito populations in the future. Because they are vectors of severalserious diseases, mosquitoes must be controlled safely and effciently.Using of botanicals as mosquito control agents can be efficient due totheir eco-safety, negligible resistance, reduced number of applications,higher acceptability, and suitability for rural areas.

Flies

House flies

The house fly, (Ms. domestica), is a well-known cosmopolitan pest fromboth farm and home environment. Excessive fly populations are notonly an irritant to farm workers but also a public health problem whichmay occur, when human habitations are located in the nearbysurroundings. Microorganisms are picked up by flies from garbage,sewage and from other sources of filth, and carried on their mouthparts,

Fig. 4: Morphological malformations of house flies treated as larvae (3rdstage larvae) with some essential oils. A. Normal larva. B-D.Malformed larva, showing signs of pigmentation. B. Curved larvawith tow central dark spots. C. Macerated larva with weektransparent cuticle. D. Larviform puparium. E. Normal pupa. F-I.Malformed pupae. F. Pupa with week puparium, G. Larviform pupa,pigmented with small dark spots at the intersegmental regions. H.C- shaped pupa with anterior constriction and small patches of blackpigments (arrow heads). I. Failure of adult eclosion.J. Normal adult.K. Malformed adult, adult with poorly developed wings and legs.Adapted form Khater (2003


through their vomitus, feces and contaminated external body parts tohuman and animal food. Mu. domestica is ubiquitous insect that hasthe potential to spread a variety of pathogens to humans and livestock.They are mechanical carriers of more than hundred human and animalintestinal diseases and are responsible for protozoan, bacterial,helminthic, and viral infections (West, 1951). Sesame, nigella and onionoils induced larvicidal effect and adversely affect pupation and adultemergence rates of the housefly, Fig. 4 (Khater, 2003). Add detailsCamphor, onion, peppermint, and chamomile oils repelled flies (Mu.domestica, Stomoxys calcitrans, Haematobia irritans, and Hippoboscaequina infecting buffaloes in Egypt for almost 6 days post-treatment,Fig. 5. No adverse effects were noted on either animals or on operatorsafter exposure to the applied oils, (Khater et al., 2009).

Kumar et al. (2011) investigated the insecticidal efficacy of sixessential oils [peppermint, M. piperita; bergamot mint, Mentha citrata;blue gum, Eu. globulus; lemongrass, Cy. citratus, and khus grass, Vetiverzizanoides, and turmeric, Cr. longa] for repellent, larvicidal and

Fig. 5: Repellent effect of essential oils applied to water buffaloes, with anaverage body weight of 400 kg, were treated. Buffaloes were groupedinto six groups, 8 animals per group, and doses of each compound(2.5 L of each DD) were poured on along the backline of the animal,1.4, 2.9, 3.6, 3.4, and 0.6 ml/kg b.w. for camphor, onion, peppermint,chamomile, d- phenothrin, respectively. In the untreated controlgroup, animals were treated with distilled water and few drops oftween 80. The repellent effect and protection time of the appliedmaterials toward flies, Musca domestica, Stomoxys calcitrans,Haematobia irritans, and Hippobosca equia, were checked daily for10 days post-treatment, Flies were counted from a distance of 2 maway from the animals. Adapted from Khater et al. (2009)


pupicidal activities against the housefly, Mu. domestica. Subsequently,emulsifiable concentrate (EC) formulations of the two most effectiveoils were prepared and tested in the laboratory as well as in the field.In repellency bioassays, M. piperita (RC84, 61.0 µg/cm2) was found to bemost effective, followed by Eu. globulus (RC84, 214.5 µg/cm2) and Cy.citratus (RC84, 289.2 µg/cm2). Formulated M. piperita and E. globulusshowed RC84values of 1.6 µg/cm2and 4.1 µg/cm2, respectively. FormulatedM. piperita and Eu. globulus achieved larval mortality (LC50) in 72 h at5.12 µg/cm2and 6.09 µg/cm2, respectively. In pupicidal bioassays, crudeoils of M. piperita and Eu. globulus suppressed the emergence of adultflies by 100%. Field experiments with the M. piperita formulationshowed reductions in fly density (number of flies/h) of 96% on treatedcattle and 98% on treated plots.

The insecticidal activity of 34 essential oils, extracted from plants,was screened against the house fly, Mu. domestica L. under laboratoryconditions. Essential oils from Pogostemon cablin proved to be the mostefficient at a lethal dose of 3 µ µg/fly after topical application (Pavela,2008).

Plant EOs possess diversified insecticidal properties. Underscreening programme of survey of bioactive agents for insect control,31 essential oils from different botanicals (2% in acetone), were studiedby Singh and Singh (1991) for repellency and direct toxicity (insecticidaleffect) against laboratory bred Mu. domestica. the authors found thatthe EOs obtained from Ocimum gratissimum L., Thymus serpyllum L.(Th. serpyllum), Illicium verum Hooks, f. (Il. verum), Myristica fragransHoutt., Curcuma amada Roxb. showed 100% repellent activity, and Ac.calamus and Th. serpyllum. showed about 40% insecticidal activity.Shalaby et al. (1998) found that lethal doses of citrus oils, applied tomature house flies, reduced the number of eggs delivered in a ratio of50% per single female. In addition, repellency has been noted for moreessential oils against the housefly (Maganga et al., 1996). Thesesecondary impacts may play a main role in the total decrease in thepopulation of insects.

Blow flies

Myiasis, infestation of tissues with dipterous fly larvae, is asignificant medical and veterinary problem that affects human andanimal welfare and national economies. Larvae of the green blowfly,Lucilia sericata (L. sericata) are facultative ectoparasites that infestsuppurative wounds. Khater and Khater (2009) assessed the toxicityof some Egyptian oils against L. sericata la rvae. The LC50 valueswere 2.81, 4.60, 6.93, and 7.92% for (Trigonella foenum-graecum),


Fig. 6: Morphological abnormalities after treatment with essential plantoils. Larval abnormalities include: (1) a small, shrunken larva withdiffuse brown pigment; (2) a weak cuticle with ulceration (arrow);(3) a weak cuticle with ulceration (arrows) and patches of brownpigment; and (4) a twisted larva with diffuse brown pigment. Pupaldeformations include: (1) a puparium with an abnormal eclosionfissure; (2) a larviform puparium; (3) a small cracked pupariumwith a central groove (arrow); and (4) a small and distortedpuparium. Adult anomalies include: (1) a deformed wing; (2) adeformed wing and legs; (3) a crumpled wing and deformed legs;and (4) a small, crumpled, poorly developed adult, Adapted fromKhater et al. (2011)


celery (Ap. graveolens), radish (Raphanus sativus), and mustard(Brassica compestris), respectively. The adverse effects on larvaltreatment also included the survival of pupae and adults. Thepupation rate was strongly decreased after treatment with 16%fenugreek and celery. Moreover, adult emergence was suppressedafter treatment of larvae with 8% mustard, 12% radish, and 16%fenugreek and celery oils. The number of emerged males exceededthe number of females, which could lead to population decline.Morphologic abnormalities of larvae, pupae, and adults were recordedafter treatment with all tested oils (Fig. 6).

In the same regard, some other Egyptian oils were highly toxic to L.sericata larvae, with LC50 of 0.57%, 0.85%, 2.74%, and 6.77% for lettuce(Lactuca sativa), chamomile (Matricaria chamomilla, Ma. chamomilla),anise (Pimpinella anisum, Pm. anisum), and rosemary (Rs. officinalis)oils, respectively. Pupation rates were markedly decreased aftertreatment with 8% lettuce oil, and adult emergence was suppressed by2% lettuce and chamomile oils. Morphological abnormalities wererecorded after treatment with all tested oils, and lettuce was the majorcause of deformation. There was a predominance of males over females(4:1) after treatment with lower concentrations of chamomile androsemary; such a skew toward males would lead to a population decline(Khater et al., 2011).

Low concentrations of some extracts, such as American wormseed,Chenopodium ambrosiodes, and thyme, Th. vulgaris (Morsy et al., 1998)are effective against L. sericata. The volatile oils of dill, Anthemgraveolens, and burnoof, Conyza dioscoridis, effectively controlled L.sericata (Mazyad et al., 1999); moreover, the same oils induced greatretardation of larval development of Parasarcophaga aegyptiaca (LC50

were 70 and 150 ppm, respectively) (Hussien, 1995).

House hold and structural pests

Putting red cedar blocks or sachets in closets to repel clothing moths isa common practice. Therefore, many hope chests are made of red cedarfor protection of heirloom clothing. Pioneers in the American West placedthe ripe fruit of the osage orange (hedgeapple) (Maclura pomifera) incupboards to repel cockroaches and other insects. The fruit has acompound irritating to the feet of an insect that will cause that insectto spend less time in a treated area. Its oil contain numeroussesquiterpenoids many of them were repellent to the German cockroach,Blattella germanica L. (Peterson & Coats, 2001). In addition, cineole,geraniol and piperidine found in bay leaves, Laurus nobilis, possessrepellent properties towards cockroaches (Verma & Meloan, 1981).


Some essential oils of Chinese medicinal herbs repel the Germanecockroach such as Angelica sinensis, Curuma aeruginosa, Cyperusrotundus, Eucalyptus robusta, Il. verum Lindera aggregate, Oc.basilicum, and Zanthoxylum bungeanum (Liu et al., 2011).

Manzoor et al. (2012) evaluated the toxicity, repellency and fumigantactivity of three essential oils that is, Cy.citratus, Mentha arvensis (M.arvensis), Eu. citriodora against Pr. americana under laboratoryconditions. Cy. citratus showed the maximum toxicity (20 to 100%)between 2 to 24 h intervals, repellency (100%) and 70 to 100% fumigationafter 24 h exposure. Eucalyptus (Eu. citrodora) oil was found to haveleast toxicity, repellency and fumigant activity. Percentage mortality(0 to 80%) between 2 to 24 h, 40 to 60% fumigant activity was observedafter 24 h at different concentrations. oils were arranged according tothe following order of preference that is, Cy. citratus, M. arvensis andEu. citriodora.

d-Limonene is used mainly for controlling structural pests as termitein California, and other plant oils (clove, peppermint, etc.) are used inthe USA by professional pest control operators as ‘flushing agents’ forcockroach control and for ‘perimeter treatments’ of homes against antsand termites, suggesting that repellence makes a strong contributionto the efficacy of these products (Isman et al., 2011).

The mechanism of the insecticidal property ascribed to geraniolwas investigated by testing its neurophysiological effect in Pr.americana (the American cockroach) and Blaberus discoidalis(discoids).Geraniol suppressed spontaneous and stimulus-evokedimpulses recorded extracellularly in the abdominal nerve cord, butincreased spontaneous firing at lower doses (threshold 2.5 × 10–4 M).Geraniol produced dose-related biphasic effects on dorsal unpairedmedian neurons. Low doses of geraniol (threshold ca. 10–4 M) reversiblyincreased the frequency of spontaneous foregut contractions andabolished these at 2 × 10–3 M (together with response to electricalstimulation) (Price & Berry, 2006).

The essential oil extracts of six Malaysian plants, i.e. Cr. longa, Zn.officinale, Pandanus odorus, Cn. zeylanicum, Sy. aromaticum and Cy.citratus, were evaluated for repellent activity against Pr. americanausing a modification of the ‘two-cylinders’ method. Dose-dependentrepellency ranging from 57.1 to 100% was exhibited by all six extractsat the lowest concentration tested (12 ppm) (Ahmed et al., 1995).

Vetiver (Vetiveria zizanioides) essential oil obtained by steamdistillation of aromatic roots contains a large number of oxygenated


sesquiterpenes. This oil is known to protect clothes and other valuablematerials from insect attack when placed inclosets, drawers, and chests,see koul et al. (2008).

Regarding termite control, EOs act as a wood preservative solutionby mixing eucalyptus essential oils with pyrethroids and borax (Urabe,1992). A series of experiments to assess the repellency and toxicity ofpatchouli oil and its main constituent, patchouli alcohol, against theFormosan subterranean termite, Coptotermes formosanus Shiraki (Cp.formosanus) recealed the repellency and that paper filters treated withpatchouli oil were less consumed by worker termites (Zhu et al.,2003).Sand treated with vetiver oil, Cp. formosanus Shiraki, or its component,nootkatone, at 100 µg/g substrate were effective barriers to termites asthey disrupted tunneling behavior of termites. As a consequence, after21 d, wood consumption and termite survival were significantly loweredcompared with cedrene-treated or untreated sand treatments(Maistrello et al., 2001).

Repellency and toxicity of 8 essential oils (vetiver grass, cassialeaf, clove bud, cedarwood, Eu. globules, Eu. citrodora, lemongrassand geranium) were evaluated against the Formosan subterraneantermite, Cp. formosanus. Vetiver oil proved the most effectiverepellent because of its long-lasting activity. Clove bud was the mosttoxic, killing 100% of termites in 2 days at 50 ¹g/cm2. Vetiver oildecreased termite tunneling activity at concentrations as low as 5¹g/g sand. Tunneling and paper consumption were not observed whenvetiver oil concentrations were higher than 25 ¹g/g sand. Bioactivityof the 8 oils against termites and chemical volatility were inverselyassociated. Listed in decreasing order of volatility, the majorconstituents of the 8 oils were: eucalyptol, citronellal, citral,citronellol, cinnamaldehyde, eugenol, thujopsene, and both ®- and -vetivone. Consequently, vetiver oil is a promising novel termiticidewith reduced environmental impact for use against subterraneantermites (Zhu et al., 2001).

Park and Shin (2005) evaluated essential oils from herbaceous andwoody plants as potential fumigants against Japanese termites andreported that clove bud and garlic oils showed the most potentantitermitic activity among the plant EOs. The termiticidal propertiesof decanal, cinnamic acid, and its derivatives on Cp. formosanus havebeen proven (Kartal et al., 2006).

The anti-termitic activities of 11 essential oils from three species ofconiferous tree against Cp. formosanus were investigated using direct


contact application. At the dosage of 10mg/g, the heartwood and sapwoodessential oils of Calocedrus macrolepis var. formosana (C.m. formosana)and Cryptomeria japonica and the leaf essential oil of Chamaecyparisobtusa var. formosana had 100% mortality after 5 d of test. Among thetested essential oils, the heartwood essential oil of C.m. formosana killedall termites after 1 d of test, with an LC50 value of 2.6mg/g, exhibitingthe strongest termiticidal property. The termiticidal eVect of heartwoodessential oil was due to its toxicity and its repellent action (Cheng etal., 2007). For more information about control of structural pests, seeAshley et al. (2006) and Brown (2012).

Lice

Human lice

Control of human lice, several studies have demonstrated the in vitropediculicidal efficacy of some essential oils towards head lice, P.h.capitis. Eucalyptus (Eu. globules), rosemary and pennyroyal (Menthapulegium , M. pulegium), a member of the mint genus, oils were foundto be least, if not more, effective than d-phenothrin and pyrethrum,two commonly used pediculicides (Yang et al., 2004a).

Essential oils from Eu. globulus and its major monoterpene 1,8-cineole showed toxicity against human head lice, P.h. capitis more thanthat of commercially used pediculides—delta-phenothrin or pyrethrum.The LT50 value of essential oil was 0.125 mg/ cm2 compared to 0.25 mg/cm2 of commercial pediculides (Yang et al., 2004b). The fumigant toxicity/repellent activity of essential oil eucalyptus from Eu. cinerea, Eu.viminalis and Eu. saligna, against permethrin-resistant human headlice with KT50 (time for 50% knockdown) values of 12.0, 14.9 and 17.4min, respectively (Ceferino et al., 2006).

Essential oils, in particular, pennyroyal, tea tree and anise, havepotent insecticidal activity for killing head lice and their eggs(Williamson, 2007). Citronellal, cotronellol, citronellyl or a mixture ofthese have been patented as pest treatment composition against humanlouse (Ping, 2007).

Studies have demonstrated the in vitro pediculicidal efficacy of someessential oils against female head lice. Eucalyptus (Eu. globules),rosemary, and pennyroyal (M. pulegium, a member of the mint genus)oils were found to be at least as effective, if not more so, against P. h.capitis than d-phenothrin and pyrethrum, two commonly usedpediculicides (Priestley et al., 2006). Essential oils, in particular,pennyroyal, tea tree and anise, have potent insecticidal activity against


head lice and their eggs. Eu. globulus leaf oil-derived monoterpenoidsare highly toxic to eggs and females of the human head louse(Gurusubramanian & Krishna, 1996). Pennyroyal and its benzylcomponent are effective repellents against P. h. capitis (Yang et al., 2004b).

Ovicidal efficacy against P. h. capitis were 68.3%, 44.4%, and 3.3%for the “suffocation” pediculicide, the melaleuca oil and lavender oilpediculicide (TTO/LO), eucalyptus oil and lemon tea tree oil pediculicide(EO/LTTO) (Barker & Altman, 2011). Anise oil demonstrated repellenteffects against a wide range of insects, such as the human head louse,P.h. capitis (Whitledge, 2002).

Some essential oils, Artemisia species, Ant. sowa, Cr. longa, andLippia alba (Li. Alba). Clove, rosemary, thyme, eucalyptus and variousmint species, have demonstrated contact and fumigant toxicity to awide spectrum of insects, including human head lice (Toloza et al., 2008).It worth to mention that Artemisia is a well-known deworming plant(Seddiek, et al. 2011).

A neem seed extract contained in a fine shampoo formulation (WashAway® Louse) blocked the aeropyles of the eggs (nits) of head and bodylice, P.h. capitis and Pediculus humanus corporis, thus preventing theembryos of both races of lice from accessing oxygen and from releasingcarbon dioxide. Thus, this product offers a complete cure from head liceupon a single treatment, if the lice (motile stages and eggs) are fullycovered for about 10 min (Mehlhorn et al., 2011). It was shown that theactive compound in MiteStop® eliminates P.h. capitis (Abdel-Ghaffar etal., 2010).

EOs contain monoterpenoids, which have lousicidal and ovicidaleffects against clothing lice, Pediculus humanus (P. humanus) (Priestleyet al., 2006); peppermint and rosemary oils were reported to controlsuch louse (Veal, 1996). Furthermore, peppermint and rosemary oilsare reported to control such lice (Palevitch & Craker, 1994).

Animal and bird lice

Some Egyptian oils have pronounced pediculicidal activity against thebuffalo louse, Haematopinus tuberculatus (H. tuberculatus), Fourminutes post-treatment, the median lethal concentration, LC50, valueswere 2.74, 7.28, 12.35, 18.67 and 22.79% for camphor (Cinnamomumcamphora, Cn. camphora), onion (Al. cepa), peppermint (M. piperita),chamomile (Ma. chamomilla) and rosemary oils (Rs. officinalis),respectively, whereas for d-phenothrin, it was 1.17%.The lethal time(50) (LT50) values were 0.89, 2.75, 15.39, 21.32, 11.60 and 1.94 min


Fig 7. In vivo pediculicidal activity of some oils against buffalo louce. Forty-eight water buffaloes, with an average body weight of 400 kg, weretreated. Buffaloes were grouped into six groups, 8 animals per group,and doses of each compound (2.5 L of each diagnostic dose) werepoured on along the backline of the animal, 1.4, 2.9, 3.6, 3.4, and 0.6ml/kg b.w. for camphor, onion, peppermint, chamomile, and d-phenothrin, respectively. In the untreated control group, animalswere treated with distilled water and few drops of tween 80. Adaptedform Khater et al. (2009).

after treatment with 7.5% camphor, onion, peppermint, chamomile,rosemary and dphenothrin, respectively. All the materials used exceptrosemary, which was not applied, were ovicidal to the eggs of H.tuberculatus. Essential oils have pronounced in vivo pediculicidalactivity as the number of lice infesting water buffaloes in Egypt wassignificantly reduced 3, 6, 4, and 6 days after treatment with theessential oils of camphor, peppermint, chamomile, and onion,respectively, Fig. 7 (Khater et al., 2009).

Tobacco (Nicotiana tobaccum), tubli (Derris philippinensis),makabuhay (Tinosphora rumphi) and neem (Az. indica) atconcentrations of 10%, 20% and 40% in oil emulsion induced more than90% mortality in Carabao louse, H. tuberculatus in vitro, whereas invivo experimentation showed that only tobacco and makabuhay induced


45.91% and 79.67% reduction in louse infestations, respectively (Robles,2004).

A single treatment of dogs with neem seed preparations, MiteStop®

or Wash Away Dog, killed motile stages and eggs of the chewing lice,Trichodectes canis, and the bloodsucking lice, Linognathus setosus. Inboth cases, the product had been left for 20 min. onto the hair before itwas washed away just with normal tap water (Mehlhorn et al., 2012).Theprevious product (diluted 1:20 with tap water) usefully controlledchewing lice, Werneckiella spp. infesting horses belonging to short hairand long hair races. A hidden infestation with these biting lice hadexisted, which became visible when the product was brushed onto thehair. Furthermore, this treatment of horses stopped the forming ofdandruff of the skin of the horses, which, in case of heavy mallophageinfestations, had looked like being powdered (Al-Quraishy et al., 2012a).

When dipping (just in–out) the infested birds completely into the1:33 tap water-diluted MiteStop® solution, it was noted that after drying(1 h) the feathers, all motile stages (nymphs and adults) of the “shaftlouse” Menopon gallinae, the elongate feather louse Lipeurus caponis,or Columbicola sp. were dead. Also, the same product induced ovicidaland repellent effects. When treating in vitro cutoff featherscontaminated with the bird louse, Lipeurus caponis, it was seen underthe stereomicroscope, that the mallophages tried to run away from the1:33 water-diluted active compound indicating that there is a repellenteffect of the neem seed extract, MiteStop® (Al-Quraishy et al., 2012b).

Other insects

Neem oil repelled sand flies under laboratory and field conditions.Concentrations of 2% neem oil mixed in coconut or mustard oil provided100% protection against Phlebotomus argentipes throughout the nightunder field conditions; against Phlebotomus papatasi it repelled sandflies for about 7 h in the laboratory. Neem oil is an indigenous productand a low-cost alternative for personal protection against sand fly bites(Sharma & Dhiman, 1993).

Large number of essential oils repels arthropod species. A neemextract proprietary product, AG1000, has been shown to be repellent tothe biting midge Culicoides imicola, which can spread cattle diseases(Braverman et al., 1999).

Flea control products for companion animals based on d-limonene,a constituent of citrus peel oil, or oils of peppermint, cinnamon, clove,thyme and lemongrass, have been introduced recently. MiteStop®, a


neem- based product, acts very specifically against beetles from thefamilies Tenebrionidae and Dermestidae, the larvae of which may enterthe plumage of poultry and feed on tiny feathers or on skin debris(Walldorf et al., 2012). Rue, Ruta graveolens L. (Rutaceae), is atraditional medicinal plant known to prevent the attacks by fleas andother noxious insects (see De Feo et al., 2002).

Sfara et al. (2009) evaluate the fumigant and repellent activity offive essential oils (eucalyptus, geranium, lavender, mint, and orangeoil) and seven monoterpenes (eucalyptol, geraniol, limonene, linalool,menthone, linalyl acetate, and menthyl acetate) on first-instar nymphsof the bloodsucking bug Rhodnius prolixus Stahl (vector of Chagasdisease in several Latin American countries). Fumigant activity wasevaluated by exposing the nymphs to the vapors emitted by 100 ×l ofessential oil or monoterpene in a closed recipient. The knockdown time50% (KT50) for eucalyptus essential oil was 215.6 min (seven timesless toxic than dichlorvos, a volatile organophosphorus insecticide usedas a positive control). The remaining essential oils showed a poorfumigant activity: <50% of nymphs were knocked down after 540 minof exposure. The KT50 values for monoterpenes, expressed in minutes,were as follows: 117.2 (eucalyptol), 408.7 (linalool), 474.0 (menthone),and 484.2 (limonene). Eucalyptol was 3.5 times less toxic thandichlorvos. No affected nymphs were observed after 540 min of exposureto geraniol, linalyl acetate, or menthyl acetate. Repellency wasquantified using a video tracking system. Two concentrations ofessential oils or monoterpenes were studied (40 and 400 × g/cm2). Onlymint and lavender essential oils produced a light repellent effect at 400× g/cm2. Geraniol and menthyl acetate produced a repellent effect atboth tested concentrations and menthone only elicited an effect at 400× g/cm2. In all cases, the repellent effect was lesser than that producedby DEET, the broad-spectrum insect repellent.

Acaricidal activity

EOs and their components can be effectively used to dispel ticks andmites, both parasitic and free-living. EOs from basil, caraway, citronellaJava, clove, lemon eucalyptus, mint, pennyroyal, peppermint, rosemary,oregano, thyme, and other plants have shown a significant acaricidalactivity (Choi et al., 2004; Miresmailli et al., 2006; Saad et al., 2006;Han et al., 2010).

Ticks

Regarding eugenol, it demonstrated bactericidal, fungicidal,nematicidal, acaricidal, and insecticidal activity of eugenol on different


species (Asha et al., 2001; He et al., 2007; El-Zemity et al., 2010). Aboutthe acaricidal effect of eugenol (4-allyl-2- methoxyphenol) it has beenfound to be a promising substance for tick control. The most abundantcomponent of oil of Sy. aromaticum is commonly known as the clove oil;this phenylpropanoid is also found in plants of other families, such asLauraceae and Lamiaceae (Franz & Novak, 2009). Brown et al. (1998)demonstrated that eugenol showed acaricidal activity and inhibition ofoviposition of female of R. microplus. More recently, Martinez-Velazquezet al. (2011), assessing the acaricidal action of the essential oils ofPimenta dioica and Oc. basilicum on R. microplus larvae, found 100 %mortality for the P. dioica oil and indicated methyl eugenol (62.7 %)and eugenol (8.3 %) as the two most abundant components of this oil,probably responsible for the mortality observed. However, the authorsdid not observe any toxic effect of the Oc. basilicum oil, even at thehighest concentration tested (20 %). In addition, Eugenol, with differentsolubilizations and concentrations, is highly effective acaricide againstR. microplus and Dermacentor nitens larvae (de Monteiro et al.,2012).The repellence of eugenol against Ix. ricinus had beendemonstrated (Thorsell et al., 2006; Del Fabbro & Nazzi, 2008; Brownet al.,1998), it is speculated that methoxy group and doubly allylic centerpresent in this compound could contribute to this activity (Brown etal.,1998).

In relation to the the acaricidal effect of eucalyptus, the citriodiol, aeucalyptus essential oil based commercially available product,significantly reduced the number of tick bites in humans and it couldbe used to reduce tick-borne infections (Gardulf et al., 2004). Eucalyptusoils, Eu. citriodora, Eu. globulus, and Eu. staigeriana, could be used asan ecologically and environmentally safer acaricide against R. microplus(Chagas et al., 2002). Clemente et al. (2010) tested the acaricidal effectof Eu. citriodora (Myrtaceae) and Cy. nardus (Poaceae) essential oilsagainst the larvae of Amblyomma cajennense (Am. cajennense) andAnocentor nitens (A. nitens) tropical horse tick). The effects weresatisfactory in case of A. nitens larvae (the acaricide efficacy of bothEu. citriodora and Cy. nardus oils reached 100.0% at 50%, and 25%concentrations, respectively); both oils were less active against larvaeof Am. cajennense.

Oil of lemon eucalyptus (PMD), citronella, soybean, peppermint, andother plant essential oils repel ticks (Stafford, 2007). Eu.staigerianaand Ca.guianensis (Meliaceae) essential oils were found to cause 100%mortality in engorged female R. microplus ticks (Chagas et al., 2002;Farias et al., 2007). In addition, peppermint and spearmint (Menthaviridis) are highly effective against fed females of the cattle tick R.


annulatus (Abel-Shafy & Soliman, 2004). Geraniol (1%) showed areduction in the mean number of ticks per animal of 98.4%, 97.3%and91.3%at days 7, 14 and 21, respectively (Khallaayoune et al., 2009).

Extracts from plants were tested by researchers from the Centersfor Disease Control in Colorado - the most effective extract against ticknymphs was from the heartwood of the Alaskan Yellow Cedar,Chamaecyparis nootkatensis (Ch. nootkatensis), the most effectiveextract against tick larvae was from the heartwood of Eastern RedCedar, Juniperus virginiana. Both of these oils are readily available asa by-product of lumber production and should give the same control ofticks as permethrin, diazinon or other volatile synthetic pesticidepoisons. Safe Solutions Enzyme Cleaner with Peppermint, menthol,myrrh, garlic, Safe Solutions food-grade DE or avocado, basil, mint,rosemary, rose geranium, cedar or citrus oil emulsions were used torepel and/or kill ticks. In the same token, spraying or cleaning areaswith high tick density with Safe Solutions Enzyme Cleaner withpeppermint and salt or myrrh extracts or red cedar oil and/or rosegeranium oil or borax or Mop-Up® (sodium borate) bi-weekly is alsoeffective.

Some essential oils and their constituents are repellent againstthe tick, Ix. ricinus, essential oil of Melaleuca alternifolia (tea treeoil) in a dose of 10 µl was lethal for more than 80% of Ix. ricinus nymphswhen inhaled, after at least 90 min, with the effect being correlatedwith the duration of exposure (Iori et al., 2005). The oils of citronella(Cymbopogon spp., Poaceae), cloves (Sy. aromaticum, Myrtaceae) andlily of the valley (Convallaria majalis, Asparagaceae) had strongrepelling effect against nymphs of Ix. ricinus. Their efficacy was ofthe same magnitude as the pure reference compound DEET (Thorsellet al., 2006). phenylethyl alcohol, -citronellol, cinnamyl alcohol,geraniol, and -pinene, isolated from the EO of Dianthus caryophyllum,are repellents against Ix. ricinus (see Nerio et al. (2010) and Khater(2012) for reviews). Geranium and neem oil repel ticks. Ticks aresometimes discouraged from biting people who daily ingest garlic andnutritional yeast. They may be repelled by the smell of menthol ororegano or rose geranium EO and irritated by talcum powder, bakingsoda and/or Comet®.

Preliminary repellent activity of 14 natural products isolated fromessential oil components extracted from, Ch. nootkatensis, wereevaluated against nymphal Ixodes scapularis Say in a laboratorybioassay and compared with technical grade (DEET). Four hours aftertreatment, nootkatone and valencene-13-ol had repellent concentration


(RC)50 values of 0.0458 and 0.0712% (wt:vol), respectively; two additionalAlaska yellow cedar compounds, nootkatone 110 epoxide and carvacrolhad reported RC50 values of 0.0858 and 0.112%, respectively. Theobserved RC50 value for DEET was 0.0728% (wt:vol). Although notstatistically significantly more active than DEET, the ability of thesenatural products to repel ticks at relatively low concentrations mayrepresent a potential alternative to synthetic commercial repellents(Dietrich et al., 2006).

Botanical acaricides induce not only acute toxic effects, but alsomanifest subacute or chronic effects by impairing the reproduction ofticks, reducing egg mass and hatchability. Tetradenia riparia (Hochst)Codd essential oil induced strong acaricidal efficacy against engorgedfemales of R. microplus and adversely affect oviposition and hatchabilityof eggs (Gazim et al., 2011). Essential oil extracted from Hesperozygisringens (Lamiaceae), used on engorged R. microplus females, inhibitedthe egg laying significantly in relation to the controls and hatching wasreduced by 95% and 30%, respectively (Ribeiro et al., 2010). Commercialproduct, Neem Azal F, containing extract of neem seed oil on Hyalommaexcavatum eggs, unfed larvae and unfed adults, obtaining 100%mortality of larvae and adults at concentrations of 1,6–3,2%, in the 7thday post-treatment. Surprisingly, the first day, the hatchability of eggsincreased, but the emerging larvae were deformed and died soon after.Later on, the hatchability was seriously impaired. Similar results wereobtained in engorged R. annulatus females by Lavandula angustifolia(Lamiaceae) essential oil in an 8% concentration (Pirali-Kheirabadi &Teixeira da Silva, 2010). Using ethyl acetate extract from Palicoureamarcgravii (Rubiaceae) >50% inhibited completely the reproduction ofR. microplus females (Silva et al., 2011).

It is worth to mention that peracetic acid (PPA), a safe andecofriendly organic acid, had a great potential as acaricide againstthe cattle hard tick, R. annulatus, and the fowl tick, Argas persicus(Ar. persicus), In vitro (Khater & Ramadan, 2007). Ar. persicus is ofveterinary importance as a parasite of poultry and wild birds. PAA(0.5 %) was highly efficient in in vitro and vivo against Ar. persicuslarvae resulting 100 % mortality after 2 minutes. The lethalconcentrations, LC50 and LC95 were 0.310 and 0.503 %, respectively.The lethal time values LT50 and LT95 were 5.34 and 40.00 minutes,respectively, after treatment with PAA (0.25 %). Seven days postdipping of infested laying chickens, the reduction percentages of Ar.persicus infesting laying hens was 99.15%. In addition, PAA inhibitsmolting effectively (28%) (Khater et al., 2012). For a review of tickcontrol, see Kiss et al. (2012)


Mites

The European and American house dust mites, Dermatophagoides (Dr)pteronyssinus and Dr. farinae, have a huge impact upon human healthworldwide due to being the most important indoor trigger of atopicdiseases such as asthma, rhinitis and atopic dermatitis. Eucalyptusoils rich in cineole have been shown to be effective against Dr.pteronyssinus (Saad et al., 2006). The study of Khan et al. (2012) showed,for the first time, that N. cataria, enriched in iridoid nepetalactonesand (E)-(1R,9S)-caryophyllene, exhibited potent repellent activity forboth species of house dust mites, and has the potential for deploymentin control programs based on interference with normal house dust mitebehavior. Also, Methyl eugenol and Asarum sieboldii Miq. essential oilcontrolled Dr. farinae and toxicity was largely due to the vapor phase(Wu et al., 2012).

In the same regard, the acaricidal activity of clove (Eugeniacaryophyllata) bud oil-derived eugenol and its congeners (acetyleugenol,isoeugenol, and methyleugenol) against adults of Dr. farinae and Dr.pteronyssinus was examined using direct contact application andfumigation methods and compared with those of benzyl benzoate andN,N-diethyl-m-toluamide (DEET). Responses varied according tocompound, dose, and mite species. On the basis of LD50 values, thecompound most toxic to Dr. farinae adults was methyleugenol (0.94 µg/cm2) followed by isoeugenol (5.17 µg/cm2), eugenol (5.47 µg/cm2), benzylbenzoate (9.22 µg/cm2), and acetyleugenol (14.16 µg/cm2). Very lowactivity was observed with DEET (37.59 µg/cm2). Against Dr.pteronyssinus adults, methyleugenol (0.67 µg/cm2) was much moreeffective than isoeugenol (1.55 µg/cm2), eugenol (3.71 µg/cm2),acetyleugenol (5.41 µg/cm2), and benzyl benzoate (6.59 µg/cm2). DEET(17.85 µg/cm2) was least toxic. These results indicate that thelipophilicity of the four phenylpropenes plays a crucial role in dust mitetoxicity. The typical poisoning symptom of eugenol and its congenerswas a similar death symptom of the forelegs extended forward together,leading to death without knockdown, whereas benzyl benzoate andDEET caused death following uncoordinated behavior. In a fumigationtest with both mite species, all four phenylpropenes were much moreeffective in closed containers than in open ones, indicating that themode of delivery of these compounds was largely due to action in thevapor phase (Kim et al., 2003).

Geraniol is an effective plant-based insect repellent. Geraniol is acommon constituent of several EOs and occurs in Monarda fistulosa(N95%), ninde oil (66.0%), rose oil (44.4%), palmarosa oil (53.5%) andcitronella oil (24.8%). Geraniol has characteristic rose-like odour and


the taste (at 10 ppm) is described as sweet floral rose-like, citrus withfruity, waxy nuances. This monoterpene alcohol is a widely usedfragrance material. It is present in 76% of deodorants on the Europeanmarket, included in 41% of domestic and household products and in33% of cosmetic formulations based on natural ingredients and itsproduction exceeds 1000 metric tons per annum. In addition, geraniolexhibits various biochemical and pharmacological properties. See Chenand Viljoen (2010) for more details about geraniol. Geraniol (1%) showeda reduction in the mean number of ticks per animal of 98.4%, 97.3%and91.3%at days 7, 14 and 21, respectively (Khallaayoune et al., 2009).The previous studies indicated that EOs and their constiutents arepromising agents for controlling pest of medical and veterinaryimportance.

Pesticides of agricultural importance

Stored product pests

Food grain losses due to stored product pests during storage are a seriousproblem. Losses caused by insects include not only the direct ingestion ofkernels, but also accumulation of exuviae, webbing, and cadavers. Highlevels of the insect detritus may afford grain that is unfit for humanconsumption and qualitative and quantitative losses of the foodcommodities. Insect infestation in the storage environment providesuitable conditions for storage fungi that cause further losses. It isestimated that more than 20,000 species of field and storage pests destroyapproximately one-third of the world’s food production, valued annuallyat more than $100 billion among which the highest losses (43%) occurringin the developing world. The use of oils in stored-products pest control isalso an ancient practice. Botanical insecticides such as pyrethrum, derris,nicotine, oil of citronella, and other plant extracts have been used forcenturies (Rajapakse, 2006; Rajashekar et al., 2012).

The currently used fumigants, phosphine, methyl bromide, andDDVP (2,2-dichlorovinyl dimethyl phosphate) provoke some safetyconcerns. Insect resistance to phosphine is a matter of serious concern.Phosphine is the major cause of suicidal deaths in India. Methyl bromidehas ozone-depleting potential and DDVP has a possible humancarcinogen potential. For more information about the side effects offumigants, see Khater (2012). As a consequence, development of safealternative that could replace the toxic fumigants against stored productpests is very important.

EOs from aromatic plants have been assayed to address several cropprotection problems in pre- and postharvest situations as many plant


essential oils have fumigant action, such as those of Artemisia species,Ant. sowa, Cr. longa, and Li. alba. Isolates like d-limonene, carvones and1,8-cineole have been well documented as fumigants. Some essential oilshave bioactivity against stored product pests, such as oils of basil, citruspeel, eucalyptus, various mint species, lavender, and rosemary, but notall essential oils are active against all insect pests (Don-Pedro, 1996;Papachristos & Stamopoulos, 2002). Nutmeg oil has been determined tosignificantly impact both the maize weed, Sitophilus zeamais (St. zeamais)and the red-flour beetle, T. castaneum and demonstrates both repellentand fumigant properties (Huang et al., 1997). The exact mode of action ofthese oils as fumigant is unknown, but the oils mainly act in the vaporphase via respiratory system. For more details about fumigants, seeTripathi et al., (2009); Isman (2010), and Khater (2011, 2012).

Turmeric, garlic, Vitex negundo, gliricidia, castor, Aristolochia,ginger, Agave americana, custard apple, Datura, Calotropis, Ipomoeaand coriander are some of the other widely used botanicals to controland repel crop pests. The essential oil of Artemisia annua repels againstT. castaneum and Callosobruchus maculates. Furthermore, two majorconstituents of the essential oil of garlic, Allium sativum, methyl allyldisulfide and diallyl trisulfide were to be potent toxicant and fumigantsagainst St. zeamais and T. castaneum. The essential oil vapours distilledfrom anise, cumin, eucalyptus, oregano, and rosemary were also reportedas fumigantants and caused 100% mortality of the eggs of Triboliumconfusum and Ephestia kuehniella. Many species of the genus Ocimumoils, extracts, and their bioactive compounds have been reported to haveinsecticidal activities against various insect species. Coconut oil hasbeen found effective against the Pulse Beetle, Callosobruchus chinensis(Cal. chinensis), for a storage period of six months, when applied toVigna radiata (green gram) at 1%. Formulations of menthol were usedas protection of pulse grain from attack of Cal. chinensis. (SeeRajashekar et al. (2012) for more information).

For the protection of stored products, the toxicity of EOs of patchouli(Pogostemon spp.) and of sweet basil (Oc. basilicum) to the coleopteransSt. oryzae (rice weevil), Stegobium paniceum (drugstore beetle), T.castaneum, and Bruchus chinensis (Br. chinensis) pulse beetle and EOsof Eucalyptus or thyme to the lesser grain borer (Rhyzopertha dominica,Rh. dominica ) were determined. see Regnault-Roger et al. (2012) formore fine points.

The neem oil and kernel powder gave effective grain protection againststored grain insect pests like St. oryzae, T. castaneum, Rh. dominica,and Cal. chinensis at the rate of 1 to 2% kernel powder or oil (Pereira


&Wohlgemuth, 1982). The neem oil adhered to grain forms uniformcoating around the grains against storage pests for a period of 180–330days (Ahmed, 1994). The essential oils of plants Xylopia aethiopica, Veprisheterophylla, and Luppia rugosa are used for protection of stored grainsfrom attack of stored grain insect pests (Ngamo et al., 2007). The essentialoil derived from the flowering aerial parts of Schizonpeta multifida andits two main components, pulegone and menthone induced fumigants/insecticides effect against two grain storage insects, maize weevil (St.zeamais) and T. castaneum (Liu et al., 2011).

The repellent activity of the mixture of essential oils from Artemisiaprinceps and Cn. camphora against the adult weevils, St. oryzae andBruchus rufimanus was significantly higher than that elicited byindividual oils (Liu et al., 2006). Repellent activity may also underliethe use of these oils in the long-term protection of foods and food productsthrough their incorporation into packaging materials. Cr. longa leaf oilpossesses toxic, antifeedant, oviposition-deterrent and ovicidal activityagainst Rh. dominica (lesser grain borer), St. oryzae (rice weevil) andT. castaneum (Tripathi et al., 2002).

Concerning chemosterilants, a compound 1, 3, 7-trimethylxanthine,was isolated from seed extract of Coffea arabica. It proved effective asa chemosterilant for Cal. chinensis, causing nearly 100% sterility at aconcentration of 1.5%. At similar concentration the compound had nophytotoxic effect on the crop plant Vigna mungo. Using the compoundfor control of stored-grain pests is recommended (Rizvi et al., 1980).

On the subject of the acaricidal effect, geraniol from the oil ofPelargonium graveolens was more effective using an impregnated fabricdisc bioassay against the storage food mite, Tyrophagus putrescentiaethan benzyl benzoate with the 50% lethal dose value being 1.95 µg/cm3and 1.27 µg/ cm3, respectively (Jeon et al., 2009). Screening of severalmedicinal herbs showed that root bark of Dictamnus dasycarpuspossessed significant feeding deterrence against two stored-productinsects. For more information about control of stored product pests, seeRajashekar et al. (2012).

Pests of agriculture importance

Extracts of locally available plants in Africa can be effective as cropprotectants, either used alone or in mixtures with conventionalinsecticides at reduced rates, which indicate that indigenous knowledgeand traditional practice can make valuable contributions to domesticfood production in countries where strict enforcement of pesticideregulations is impractical.


Essential oil constituents such as thymol, citronellal and -terpineolare effective as feeding deterrent against tobacco cutworm, S. liturasynergism, or additive effects of combination of monoterpenoids fromessential oils have been reported against S. litura larvae.

Carvone is a monoterpene of the essential oil of Carum carvi. It is anon-toxic botanical insecticide used under the trade name TALENT. Itenhances the shelf life of stored fruits and vegetables and inhibitsmicrobial deterioration without altering the taste and odor of the fruitsafter treatment (Varma & Dubey, 1999). The LD50 value of carvone (inmice) is reported to be 1640 mg/kg (Isman, 2006).

Extracts of locally available plants in Africa can be effective as cropprotectants, either used alone or in mixtures with conventionalinsecticides at reduced rates, which indicate that indigenous knowledgeand traditional practice can make valuable contributions to domesticfood production in countries where strict enforcement of pesticideregulations is impractical.

The essential oil of leaves of Hyptis martiusii Benth and 1,8-cineoleshowed pronounced insecticidal effect against Bemisia argentifolii, thevectors of white fly fruit plague (Araújo et al., 2003).

Nineteen essential oils, obtained by hydrodistillation from aromaticand medicinal plants of Moroccan origin, were tested for theirinsecticidal effects on Hessian fly (Cecidomyiidae) adults and eggs. Thisinsect is the major pest of wheat in Morocco. Most of the aromatic plantsbelong to the family Labiatae. The species M. pulegium, Origanumcompactum (O. compactum), and Origanum majorana were the mosttoxic to adults; Ammi-visnaga, Pistacia lentiscus, O. compactum, andM. pulegium were more efficient on eggs (Lamiri et al., 2001).

Scott et al. (2004) recommended the use of Piper extracts berestricted to small-scale spot treatments in residential areas whereinsect pest outbreaks have occurred as they tested extracts from threespecies of the plant family Piperaceae, Pip. nigrum, Piper guineense(Schum & Thonn), and Piper tuberculatum (Jacq.) for efficacy againstinsects from five orders. All three species contain isobutyl amides,plant secondary compounds that act as neurotoxins in insects. When24-h Pip. nigrum LC50 values were compared between common insectpests from eastern Canada and the northeastern United States, themost sensitive species in order of increasing lethal concentration wereeastern tent caterpillar, Malacosoma americanum (F.) < Europeanpine sawfly larvae, Neodiprion sertifer (Geoffroy) < spindle ermine


moth larvae, Yponomeuta cagnagella [Hübner] < viburnum leaf beetlelarvae, Pyrrhalta viburni [Paykull] < stripped cucumber beetle adults,Acalymma vittatum (F.) < Colorado potato beetle adults, Leptinotarsadecemlineata (Say) < Japanese beetle adults, Popillia japonica[Newman] < hairy chinch bug, Blissus leucopterus hirtis (Montandon).The life stage tested was the point at which each species causes thegreatest amount of damage to the host plant and the point at whichmost gardeners would likely choose to treat with a conventionalsynthetic insecticide. Greenhouse trials revealed that the pepperformulations also had a repellent activity, thus protecting plant leavesfrom 1) herbivory (lily leaf beetle, Lilioceris lilii (Scopoli), adults andlarvae and stripped cucumber beetle adults) and 2) oviposition[European corn borer, Ostrinia nubilalis (Hübner)]. Combinations withother botanical extracts were additive at best in toxicity and repellenttrials. Nontarget toxicity to beneficial invertebrates is a possibilitybecause the Pip. nigrum LC50 for beneficial ladybird beetles was 0.2%.Pip. nigrum extracts can provide a reasonable level of control againstlepidopteran and European pine sawfly larvae and also will work as ashort-term repellent and feeding deterrent.

Machial et al. (2010) evaluated 17 essential oils against the obliquebanded leafroller, Choristoneura rosaceana (Cho. rosaceana), and therosy apple aphid, Dysaphis plantaginea (Dy. plantaginea) as are seriouspests in apple orchards throughout North America, also the green peachaphid, Myzus persicae (My. persicae) and the cabbage looper,Trichoplusia ni (Tr. ni). The most toxic of these were further evaluatedto determine their LC50 and LD50 values. Patchouli oil was found to beamong the most toxic to all four species. Thyme oil was also toxic toboth Cho. rosaceana larvae and Dy. plantaginea adults, while citronellaoil demonstrated high toxicity to Dy. plantaginea. Garlic and lemongrassoils were also identified as potential candidates for Tr. ni control andlavender oil was identified as the second most toxic essential oil to My.persicae.

Mixtures of plant compounds reduce the evolution of tolerance tonatural insecticides, compared to a single compound, as exemplifiedwith My. persicae.

Eugenol, abundantin cloves (Eugenia caryophyllata), orcinnamaldehyde, abundant in cinnamon (Cinnamomumverum), exertsovicidal, larvicidal, and adulticidal toxicity on the beanweevilAcanthoscelidesobtectus (Acn. obtectus)and inhibits its reproduction(Regnault-Roger & Hamraoui, 1995).


Toxicity levels of EOs to the Mediterranean fruit fly, Ceratitis capitata(Cer. capitata), and the cereal aphids Rhopalosiphum padi andMetopolophium dirrhodum have been determined. The efficacy of EOsand their constituents varies according to the phytochemical profile ofthe plant extract and the entomological target. The bruchid Acn. obtectusis more sensitive to phenolic monoterpenes and the aphid R. padi tomethoxylated monoterpenes, whereas the Mediterranean fruit fly, Cer.capitata, respond to both types of compounds. EOs such as oil of thyme,rosemary (Rs. officinalis), and eucalyptus have antifeedant or repellentactivity. The oil of citronella repels mosquitoes and flies, and garlic oilis a deterrent to many insect herbivores. Such oils are currentlymarketed to horticulturists, greenhouses, and home gardens in theUnited States and the United Kingdom. (For more details, see Regnault-Roger et al., 2012).

Park et al. (2006) carried out fumigant bioassays of an additional 40plant species to determine their larvicidal activity against L. ingenua.The best fumigant activities were obtained with EOs of horseradish(Armorica rusticana), anise (Pm. anisum), and garlic oils. The toxicityof EOs of citrus peel, in which limonene is the most abundant ingredient,was observed on Cer. capitata. Larvae were administered diets in whichthe LC50 values of limonene ranged from 7 to 11 ml g-1. (Papachristos etal., 2009).

Essential oils of cumin (Cuminum cyminum), anise (Pm. ansium),oregano (Origanum syriacum var. bevanii) and eucalyptus (Eucalyptuscamaldulensis) were effective fumigants against the cotton aphid (Aphisgossypii) and the carmine spider mite (Tetranychus cinnabarinus), twogreenhouse pests (Tuni & Sahinkaya, 1998). The potential of basil(Ocimum spp.) against garden pests has been reviewed (Quarles, 1999).

Dietary effects of a number of monoterpenoids against the Europeancorn borer (Ostrinia nubilalis) have been reported (Lee et al., 1999). Thetoxicity of a range of essential oil constituents to the western cornrootworm (Diabrotica virgifera), the two-spotted spider mite (Tetranychusurticae) (Lee et al.,1997). Mixtures of different monoterpenes produced asynergistic effect on mortality, and a proprietary monoterpene mixturewas developed containing 0.9% active ingredient for use against foliarfeeding pests (Hummelbrunner & Isman, 2001).

Alghough limonene found in sour oranges (Citrus aurantium) is toxicto adult bean weevils (Callosobruchus phasecoli), it is highly attractiveto male Mediterranean fruit flies (Jacobson, 1982). -Ocimene is repellentto the leaf cutter ant, Attacephalotis in both field and laboratoryexperiments (Harborne, 1987). Experiments with the aphid Carvariella


aegopodii, which feeds on the aromatic Apiaceae (Apiales) species insummer, indicate that the aphid can be captured in traps baited withcarvone, and repelled by linalool (Chapman et al. 1981; Harborne, 1987).Carvone occurs in the essential oils of several plants of the Apiaceae.Rosemary oil reduces the hatchability of eggs (62.65%) and adverselyaffects some biological aspects of the potato tuber moth, Phthorimaeaoperculella (Lepidoptera: Gelechiidae) (Moawad & Ebadah, 2007).

Concerning mite control, the constituents of essential oils, carvone,carvacrol, cineole, cinnamaldehyde, cuminaldehyde, eugenol, geraniol,limonene, linalool, menthol, thymol are recognized as effective againstspider mites (Miresmailli et al., 2006; Badawy et al., 2010; Lim et al.,2011). Examples of registered commercial formulations of acaricidesaimed to control of plant-feeding mites include products based oncinnamaldehyde, eugenol, cottonseed, clove and canola oils, rosemaryand peppermint oils, American wormseed oil (Copping & Menn, 2000;Miresmailli & Isman, 2006; Copping & Duke, 2007; Cloyd et al., 2009;Regnault- Roger et al., 2012). Products based on citronellol and farnesolact as attractants; they increase activity of mites which enhance theirexposure to a co-applied synthetic acaricide (Copping & Menn, 2000;Tomlin, 2009; Chandler et al., 2011).

Plant essential oils and their constituents are used as fumigants forbeehives to manage economically important honey bee ectoparasites,the varroa mite, Varroa jacobsoni (V. jacobsoni) and the tracheal mite(Acarapis woodi). In North America, menthol (from peppermint) iswidely used for this purpose (Delaplane, 1992), and in Europe thymol(from gardenthyme) is most often used (Floris et al., 2004). Tetranychusurticae (Te. urticae) and Phytoseiulus persimilis (Choi et al., 2004).

EO-based pesticides or repellents may become complementary tomore toxic chemicals and can be used in organic food production bothin field and in controlled environment. For more details about Insectand mite control in field crops, see Hertel et al. (2011). For moreinformation about using plant essential oils for pest and diseasemanagement, see Ahmed et al. (1984), Isman (2000), Regnault-Rogeret al. (2012), Khater (2011, 2012) and Rajashekar et al. (2012).

CONCLUSIONS

The environmental problems caused by overuse of pesticides haveattracted the attention of scientists in recent for development of safe,biodegradable and environmental friendly plant-based products thatcan be used to reduce synthetic pesticide use while maintaining crop


yields. EOs are long used as fragrances and flavorings in the perfumeand food industries, respectively. Essential oils demonstrate a widerange of bioactivities from direct toxicity to insects, to oviposition andfeeding deterrence as well as repellence and attraction. Most insectrepellents are volatile terpenoids, while other terpenoids can act asattractants. Repellents and attractants could be used efficiently forbehavioral insect control.

In recent years, the use of EOs as low-risk insecticides has increasedconsiderably owing to their popularity with organic growers andenvironmentally conscious consumers. Natural pest controls using EOsare safer to the user because of their low mammalian toxicity and theenvironment because they break down into harmless compounds withinhours or days in the presence of sunlight. They are also very closechemically to those plants from which they are derived, so they areeasily decomposed by of the microbes common in most soils. Predator,parasitoid and pollinator insect populations will be less impacted onaccount of the minimal residual activity.

Accordingly, the greatest beneûts from EOs might be achieved inindustrialized countries in situations, where human and animal healthare foremost – for pest control in and around homes and gardens, incommercial kitchens and food storage facilities and on companionanimals, as well as in developing countries, where human pesticidepoisonings are most prevalent.

Several commercial insecticides based on plant essential oils intendedfor professional, agricultural, veterinary and consumer applicationshave been introduced to the market in the past decades. EOs are effectiveas ‘‘stand-alone’’ products under low pest pressure, e.g., early in agrowing season. Outstandingly, they can be applied in rotation or incombination (tank-mixed) with other crop protectants, includingconventional synthetic or microbial pesticide products.

Pesticides based on plant EOs or their constituents havedemonstrated efficacy against a range of stored product pests, domesticpests, blood feeding pests and certain soft-bodied agricultural pests, aswell as against some plant pathogenic fungi. More importantly,resistance will develop more slowly to formulations based on EOs owingto the complex mixtures of constituents that characterize these oils.Commercial production of EO-based insecticides has been greatlyfacilitated by exemption from registration for certain oils, commonlyused in processed foods and beverages, which favor development of suchproducts for agricultural, industrial, and veterinary applications, and


for the consumer market. Stability of EO- based products could beprolonged by several ways, such as encapsulated formulations, whichseem to be able to protect the core material against environmentalagents and could be considered for use in controlled release systems, aswell as nanoparticles which have the potential to be used as an idealeco-friendly approach for the control of insect pests.

There are several challenges to the commercial application of plantessential-oil-based pesticides include resource availability with sufficientquantities. Even though many essential oils may be abundant andavailable year round due to their use in the perfume, food and beverageindustries, large-scale commercial application of essential-oil-basedpesticides could require greater production of certain oils. Biodiversityof plant sources is very important concern. Therefore, collection of wildplants must be properly managed, and it is preferable to select plantspecies with rapid turnover in the wild or that can be cultivated.Standardization is also a challenge as the chemical profile of plant speciescan vary naturally depending on genetic, geographic, climatic, annual orseasonal factors, and pesticide manufacturers have a duty to standardizetheir products will perform consistently. The other challenges includeprotection of technology (patents) and regulatory approval.

This complete and eco-friendly approach would afford new methodsof controlling insect pests and the diseases associated with them.Further investigations of the potential of these methods for effectivepest control and the seeking of the various plants as control agents, arealso required for making EO- based pesticides go well together withintegrated pest management programs. However, further studies inthis trend are needed to establish the shelf life, consistency and efficacyof these formulations in different settings and climatic conditions. Theway will be open for EOs in case of endorsement of strong political will,consumer awareness, and market responses. These steps forward willguarantee an increasing position in the marketplace for the near futureand help in preventing the disposal of thousands of tons of pesticideson the earth and provide residue-free food and a safe environment tolive (Khater, 2011, 2012). Unquestionably, the number and quality ofEO- based pesticides will increase and the costs will fall; accordingly,the unemployment rate will drop and the national income will increasefor the welfare of developed and developing centuries.

ACKNOWLEDGEMENTS

The author is grateful to Dr. Aza Abdel Fattah Moustafa, Professorand consultant of Insecticides at the Research Institute of Medical


Entomology, Egypt, for her interest on the subject, their precious advicesand helpful discussions; Dr. Mohamed Hafez, Plant PathologyDepartment, Faculty of Agriculture, Benha University, Egypt, for hisvaluable advice and his help for the quality of the figures; and EslamAfify, Different, Benha, Egypt, for his design for Fig. 1, Global Scenarioon the Bioactivity of Essential Oils as Green Pesticides.

LIST OF APPRECIATIONS

A: Anocentor Il: IlliciumAc: Acorus Ix: IxodesAcn: Acanthoscelides L: LuciliaAe: Aedes Li: LippiaAl: Allium Lt: LitseaAm: Amblyomma M. MenthaAn: Anopheles Ma: MatricariaAnt:Anthema Mn: ManilkaraAp: Apium Ms: MusaAr: Argas Mu: MuscaAz: Azadirachta My: MyzusB: Bovicola N: NepetaBr: Bruchuschinensis NPs: NanoparticlesC. Catharanthus O: OriganumC.m: Calocedrusmacrolepis Oc: OcimumCa: Carapa P.h.: Pediculus humanusCal: Callosobruchus P: PediculusCer: Ceratitis Pip: PiperCh: Chamaecyparis Pm: PimpinellaCho : Choristoneura PMD: a plant derived repellent, para-

methane 3–8, diolCn: Cinnamomum Pr. PeriplanetaCn: Cinnamomum R. Rhipicephalus (Boophilus)Cp: Coptotermes Rh: RhyzoperthaCr: Curcuma Rs: RosmarinusCy: Cymbopogon S: SpodopteraD. Desmodium St: SitophilusDEET: N, N-diethyl-m toluamide, Sy: Syzygiumsynthetic insect repellentDr: Dermatophagoides T: TriboliumDrs: Drosophila Te:TetranychusDy: Dysaphis Th: ThymusE: Euphorbia Tr: TrichoplusiaEOs: essential oils Tr:TrichoplusiaEu. Eucalyptus Z: ZanthoxylumH: Haematopinus Zn: ZingiberHip: Hippobosca


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