natural pesticides
TRANSCRIPT
Syed Yousuf HussainAsst. ProfessorMESCO College of Pharmacy
Pesticides are typically designed for selective toxicity to a specific organism.
The ideal pesticide should be highly selective, highly toxic, and biodegradable with a relatively short half-life
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Classification
Based on the target organism Based on the physical nature Based on the chemical nature
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Based on the target organism: Acaricides: essential oil from leaves of Melaleuca
alternifolia, Gynandropsis gynandron, eucalyptus oil etc
Insecticides: Pyrethrum, Nicotine, Rotenone, Cevadine, Veratridine, Ryonidine
Rodenticides: strychnine and scilliroside Herbicides: D-limonene (citrus oil), Vinegar,
Saltwater or salt Molluscicides: The berries of the Ethiopian plant
Phytolacca dodecandra (Phytolaccacea), saponins in Swartzia madagascariensis (Leguminosae)
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NicotineBiological Source; part usedChemistryUses
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Biological Source: Dried leaves of Nicotiana tabacum; Family- Solanaceae
Part used: Every part of the plant except the seed
contains nicotine Distribution of nicotine in the mature
plant: leaves 64% Stem 18% Root 13% Flowers 5%
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Chemistry Nicotine belongs to pyridine-piperidine type of
alkaloids Nicotine is a hygroscopic, oily liquid that is
miscible with water in its base form. As a nitrogenous base, nicotine forms salts with acids that are usually solid and water soluble
Nicotine is optically active, having two enantiomeric forms. The naturally occurring form of nicotine is levorotatory
The dextrorotatory form, (+)-nicotine is physiologically less active than (–)-nicotine.
Mode of action Acts as a nicotinic acetylcholine agonist
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Uses Insecticide Contact poison Juice of the leaves can be rubbed on the body as an
insect repellent Against: soft bodied insects like aphids, white flies, moths,
termites, butterfly-larvae, red-spider mites etc. Sprayed on crops in the form of Nicotine sulfate
(tobacco/water tea combined with sulfur) Dose: Combine 15 gm of tobacco per liter of water,
soak for one day at room temperature and strain the resultant tea.
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Rotenone
Biological Source; part usedChemistry; NatureMode of ActionUses
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Biological Source: Dried roots and rhizomes of Derris elliptica and cube root of Lonchocarpus utilis, both belonging to the family Leguminosae
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Chemistry Rotenone is an isoflavone derivative Rotenone is an odorless, colourless crystalline
substance which is insoluble in water but soluble in many organic solvents
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Mode of action
Rotenone works by rotenone acts as an inhibitor of oxidative phosphorylation,
specifically interferring with NAD oxidation. interfering with the electron transport chain in mitochondria,
i.e., it inhibits the transfer of electrons from iron-sulfur centers in
complex I to ubiquinone. This interferes with NADH during the creation of usable
cellular energy. Toxicity is characterised by conjunctivitis, pharyngitis,
rhinitis, GI upset, ulceration, nausea and vomiting, and ultimately respiratory stimulation and convulsions.
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Uses
Insecticide Contact poison Piscicide Against vegetable insects such as leaf hoppers,
Mexican bean beetle, caterpillars, aphids etc.
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Strychnine
Biological Source; part used Chemistry; Nature Mode of Action Uses
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Biological Source: Dried ripe seeds of Strychnos nuxvomica;
Family- Loganiaceae
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Chemistry Terpene indole alkaloid highly toxic (LD50 = 0.16 mg/kg in
rats, 1–2 mg/kg orally in humans
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Mode of Action
A neurotoxin which acts as an antagonist of glycine and acetylcholine receptors
Causes death by paralysis of respiratory muscles.
Strychnine causes muscular convulsions and eventually death through asphyxia.
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Uses
Rodenticide
Against moles, rats, birds etc
It is also used as an ursicide in Japan.
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Scilliroside
Biological Source; part used Chemistry; Nature Mode of Action Uses
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Biological Source:Red variety of the Europian Squill
Urginea maritima; Family- Liliaceae Part used: Dried scaly leaves of the bulbs Distinction from white squill:Reddish-brown outer scales due to
red anthocyanin pigments.
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Chemistry
Cardiac glycosides Bufadienolide Sparingly soluble in water
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Mode of Action
Rats are unable to vomit which leads to glycoside intoxication and pulmonary edema
Cardiotoxic- induces cardiac arrythmias LD50 = 0.7 mg/kg in male rats and 0.43 mg/kg in
female rats
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Uses
Red squill is specific for rats and nontoxic to other warm-blooded animals when used in recommended dosages.
The specific toxicity to rats is due to their inability to vomit while the product induces vomiting in other animal species
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Other pesticides
Cevadine and Veratridine from Schoenocaulon officinal (Liliaceae)
Effective against vegetable insects. Ryanodine from roots and stems of
Ryania speciosa (Floucortiaseae) The plant is used in the control of
various lepidopterous larvae which attack fruits, and particularly the European corn borer.
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