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INTEGRATED MOSQUITO MANAGEMENT- COMPETENT SUBSTITUTES

FOR CHEMICAL INSECTICIDES

Despite of the cutting edge technologies existing in almost all areas with medical domain

as no exception, people of the today’s world are still prone to many diseases. The

grounds for this trounce was traced to be the mosquitoes, acting as the kingpins in thedisease transmission. Mosquito borne diseases are prevalent in more than 100 countries,

infecting over 700,000,000 people every year globally and 40,000,000 people of Indian

population. Though they are small dipteran insects with a short life span, they arerecognized as the most pestiferous responsible for carrying dreadful protozoans and

viruses causing Malaria, Filaria, Dengue, Japanese Encephalitis and Chikungunya.

Hence, mosquito population control has become the sole primary requisite to achieve

quality betterment of the human life.

The quest to defeat mosquitoes led to an inexhaustible war, for the origin of the tiny

creatures have been sketched to 25 million years back, undergoing a parallel evolution for 

fine tuning their own life cycles to form an intimate relationships with their hosts. In thisregard, no single method was found apt for combating the mosquito population rather a

meticulous implementation of planned intervention programs are required to achieve thepurpose. Integrated Mosquito Management (IMM) is a decision-making process for the

management of mosquito populations, involving a combination of methods and strategies

for long-term maintenance of low levels of   vectors. It is designed to benefit or to have

minimal adverse effects on people, domestic animals, wildlife and the environment.Mosquito populations are suppressed to tolerable levels by selecting scientifically sound

suppression methods considering the ecological and economical long-term interest of 

humankind. The Integrated mosquito management includes vector surveillance, judicioususe of chemical insecticides, implementation of biologically efficient mosquito control

methods as well as exerting environmental management methods, simultaneously.

Chemical control using various insecticides though is a highly accessible and an effective

method, their cost of implementation, their bottomless impacts on the non target

organisms; simultaneously raising questions on environmental hazards due to their residual activity and development of resistance in the mosquito vectors have questioned

their usage. Thus, the Environmental Protection Act in1969 has passed a number of rules

and regulations for their implementation, which checked the usage of the chemical

control agents. Considering these set backs, biologically efficient control methods havebecome the central of the control programs in lieu of the chemical insecticides.

Therefore, a rummage for the sound ecofriendly alternates were found to be the various

biocontrol agents compatible in different water habitats and phytochemicals, the sourcesof which are the abundant botanicals. Thus our effort is to lay down the importance of 

various phytochemicals and biocontrol agents which are central to the mosquito control

programs.

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Phytochemicals

Phytochemicals are the botanicals, which are the naturally occurring insecticides obtainedfrom the plant sources. This is a no new mosquito control strategy for they were in use

since 1920s, but with the discovery of DDT in 1939, a synthetic insecticide has

sidetracked the mosquito control programs (Shaalan et al. 2005). Yet, considering theenvironmental hazards and the increased resistance in the disease vectors, refocus on

phytochemicals that are easily biodegradable and have no ill effects on nontarget

organisms were appreciated. Since then, the search for new bioactive compounds fromthe plant kingdom has been extensive. The present phytochemicals makes up to 1% of the

world’s pesticide market.

The reasons supporting the increasing use of phytochemicals are the abundant availabilityof plant species in most geographical areas around the world, comprise an array of 

chemicals which reduces the chances for resistance development and harbors a range of 

deleterious effects on both behavioral and physiological process (Sukumar et al., 1991).

Botanicals are basically the secondary metabolites serving as a means of defensemechanism of the plants to withstand the continuous selection pressure from predators

and other environmental factors (Shaalan et al., 2005). These natural insecticides enhancemosquito control with their biological activities such as insect growth regulators,

repellents, ovipositional attractants, deterrents, anti-feedants, inhibitors of growth, anti-

reproductive agents, where as some show larvicidal activity, reduce fecundity and also

reduce viability of mosquito eggs, etc.

The most promising botanicals belong to the families of Meliaceae, Rutaceae,

Asteraceae, Annonaceae, Labiatae and Canellaceae. Pyrethrin was the first discoveredherbal insecticide extracted from Chrysanthemum cinerarifolium flowers (Hartzell and

Wilcoxon, 1941). Phytochemicals extracted from Old litter of Alnus glutinosa, leaves of Azadirachta indica, latex and roots of  Calotropis procera show mosquito larvicidalactivity, Ajugarins from Ajuga remota are Insect growth regulators, Insect repellents are

obtained from Azadirachta indica, curcuma aromalica, Callistemon rigidus, Citronella,Vitex negundo, Mosquito coils are made with finely ground pyrethrum daisy flower heads, coconut husk or saw dust, and the Commonly used plants for Natural fumigants

are Azadirachta indica, Ocimum sp, Corymbia citriodora, etc. The chemical constituents

of the phytochemicals are terpenoids, phenolics, alkaloids, etc. 

The major advantage of phytochemicals is that the whole plant can be used for extraction

like Melalenca alternifolia, or specific part like leaves (Calophyllum inophyllum), stem,

barks (Azadiracta indica), flowers (Chrysanthemum cinerariform), fruits (Piper longum),seeds (Solanum sodomaeum) and roots can be used. The preparation methodology is

usually simple, facilitated using minimal technology. Thorough screening should be

performed for the activity varies significantly depending on plant species, plant part, ageof plant part, solvent used in extraction and mosquito species. Various formulations can

be developed from either the crude dusts as pyrethrum, extracts or resins (pyrethrins,

neem seed oils) or the isolates of interest are refined as the d-limonene, linalool which is

used in mosquito repellents. Besides possessing many strengths like no resistance

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development, there exits very few limitations like rapid degradation and posing little risk 

to macro invertebrates (Kreutzweiser (1997).

Biocontrol agents

Biological control is an age old practice first introduced by the ancient Egyptians. It is aconventional method aiming at the weakest link of the life cycle of the mosquito, most

cases targeting the larval life stages. It is defined as the action of natural enemies in

maintaining the density of the other organism at a lower average than would occur intheir absence. The biocontrol agents may include insects, viruses, bacteria, protozoa,

fungi, nematode worms and fish. The effective use of these agents requires a thorough

understanding of the biology and behavior of the mosquitoes as well as the local

environmental conditions. Biocontrol agents play a collective role in keeping theecosystem in balance and help to maintain the mosquito numbers low.

Not all organisms are used in the control programs. Agents which are host specific, show

lethal parasitism, which can be easily manipulated in the laboratory, can be massproduced, has potential recycling activity for an extended period, and with a shelf life of 

at least one year and ecofriendly are only implemented in the control programs.Suppression of vector population by biocontrol agents is achieved either by inoculation of 

exotic natural enemies or by inundation of already existing organisms into the mosquito

habitats. In this regard, predators, parasites or pathogens provide as the alternate means of 

the control methods. As a rule, mosquito pathogens and parasites are highly specific totheir host, whereas predators are more general in their feeding habits and

opportunistically feed on mosquitoes.

A wide variety of species are utilized as potential larvicides or adulticides in the mosquito

control programs. Among these the mosquito pathogens used as the control agents

include assorted bacteria of which the Bacillus thuringiensis var israelensis and B.

sphaericus are most important (Magda A. El-Bendary, 2006). These bacterial spores produce

characteristic toxins which upon ingestion lead to osmotic lyses of the larval gut followed

by death. Many formulations have been developed as they are easy to be manipulated andimplemented. The ubiquitous fungal species such as such as Lagenidium giganteum

(Vyas et al, 2007), Metarhizium, Coelomomyces and Culicinomyces (Scholte et al., 2004 )and

the microsporidians belonging to Protozoa like Amblyospora and Nosema

algerae(Kellen, 1965) and viruses belonging to Iridoviruses, densonucleoviruses, nuclear polyhedrosis viruses, cytoplasmic polyhedrosis viruses and entomopox viruses are also

found to have renowned importance. These pathogens multiply rapidly consuming

nutrients and destroy internal organs of the host, followed by the larval tissuedisintegration and dissemination into the water for ingestion by uninfected larvae.

The other group of biocontrol agents is the parasitoids that have an immature life stage todevelop on or within a single insect host, ultimately killing the host. Mosquito parasites

are ingested by the feeding larvae and once inside the host, parasite consumes the internal

organs and food reserves until the developmental process is complete. Finally the host is

killed when the parasites matures and leaves the host. Romanomermis culicivorax

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belonging to the phylum Nematoda, are used to control culicines breeding in semi-

polluted water, anophelines breeding in fresh waters and also tree-hole breeders likeAedes albopictus(Kerwin, 1985). These nematode eggs were commercially produced andsold under the name Skeeter Doom TMR.

The third class of biocontrol agents are the mosquito predators which comprise of complex organisms including both invertebrates and vertebrate Predators are

opportunistic in their feeding habits and are represented by the members of 

platyhelminthes, other insects, crustaceans species, fish ,birds and bats that consumelarval or adult mosquitoes as prey. Toxorhynchites rutilus rutilus is also a mosquito

species which shows cannabilistic activity on other larvae of container breeding and tree-

hole inhabiting mosquitoes such as Culex and Aedes (Collins. L.E and Blackwell, 2000).

During its development, one Toxorhynchites larva requires approximately 5000 first-instar prey larvae and 300 fourth-instar prey larvae, so an inundative release provides a

long term control against container breeding mosquitoes. Dugesia, commonly known as

Turbellarians, is the potential control agent of fresh water mosquito larvae (Suprakash

Kar and A. K. Aditya., 2003). It is an effective aquatic predator of the Culex mosquitoeggs, larvae and pupae by immobilizing the larvae with its mucus secretions. The other 

predators include copepods namely Mesocyclops albidus which feed voraciously on thefreshly hatched mosquito larvae (Marten, 1989). M. albidus can survive for months at 0º

C and are not killed by any pesticides commonly used for mosquito control. Among the

predators, the mosquito fish, Gambusia affinis is extensively used as the biocontrol agent

for mosquitoes in ponds, canals, irrigated fields and some other freshwater sources .They can eat 100 to 500 larvae per day and produce 3 to 4 broods each year. The fish

lives two to three years and are live-bearers. Besides this, Cyprinodontidae known as

killifish and Poecilia reticulata which has the ability to withstand high levels of chemicaland organic pollutants are considered important. Mosquitoes form a small portion of the

bird purple martin and the bat’s diet, though not significant to be used as the efficient

control agents.

Despite of many prospects, there are few drawbacks as each biological control agent is

host-specific, pose difficulty in mass production, require highly trained personnel toassess the efficacy and is not applicable in all mosquito breeding habitats. Moreover the

level of control may not be sufficient with high research costs.

Thus, mosquito control using natural products either of plant or microbial origin wasfound to be fruitful (Consoli and Oliveira, 1994) though this strategy reduces, but does

not eradicate, pest populations. The future of biological control is promising, but this

tactic will constitute just one of many pest management options. Many obstacles willneed to be overcome before biological control can reach its full Potential. Hence, studies

for identification of efficient phytochemicals were recommended because they are eco-

friendly, promising, more selective and easily degradable and also inexpensive, and arereadily available (Rajkumar, et al., 2005). Plant products have multiple usages as

insecticides for killing larvae or adult mosquitoes or as repellents for protection against

mosquito bites, depending on the type of activity they possess. Where as the success of a

biocontrol program will depend on level of suppression attained and the tolerable level or 

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economic threshold of the pest. Biocontrol agents certainly holds the possibility of 

becoming a more important tool and playing a larger role in mosquito control in the

future when improved technology and more attractive economics may enhance itsusefulness.

References

1) K. Sukumar, M.J. Perich and L.R. Boobar, Botanical derivatives in mosquito

control: a review, J Am Mosq Contr Assoc 7 (1991), pp. 210–2372) Shaalan E.A.-S., Canyon D., Younes M.W.F., Abdel-Wahab H., Mansour A.-H.

A review of botanical phytochemicals with mosquitocidal potential Environment International , (2005) 31 (8), pp. 1149-1166

3) Collins. L.E and Blackwell The biology of Toxorhynchites mosquitoes and their potential as biocontrol agentsBiocontrolNews and Information 2000 Vol. 21 No. 4

4) Magda A. El-Bendary Bacillus thuringiensis and Bacillus sphaericus

biopesticides production Journal of Basic Microbiology  Volume 46, Issue 2  ,

Pages 158 – 1705) Vyas, Neetu1; Dua, K.; Prakash, Soam Efficacy of  Lagenidium giganteum

metabolites on mosquito larvae with reference to nontarget organismsParasitology Research, Volume 101, Number 2, July 2007 , pp. 385-390(6)

6) Scholte E-J, Knols BGJ, Samson RA, Takken W. 2004. Entomopathogenic fungi

for mosquito control: A review Journal of Insect Science, 4:19,

7) Kellen, W. R. 1965. Microsporidia as parasites of mosquitoes. Proc. Internatl.Cong. Ent., London 12: 728-29.

8) Kerwin, J. 1985b. Recycling of  Romanomermis  culicivorax (Mermithidae:

Nematoda) in rice fields in Calif. USA. J. Med. Ent. 22(6): 637-643.9) Suprakash Kar and A. K. Aditya.  Biological control of mosquitoes by aquatic

planaria. Tiscia (2003): 34, 15-18.

10) Marten G. G. A survey of cyclopoid copepods for control of  aedes albopictus

larvae Bull. Soc. Vector Ecol., (1989) 14(2): 232-236

11) Anupam Ghosh, Samir Mandal, Indranil Bhattacharjee, Goutam Chandra

Biological Control of Vector Mosquitoes by Some Common Exotic FishPredators Turk J Biol 29 (2005) 167-171