Insecticides of plant origin (Botanicals)
The Insecticides of plant origin extracted from seeds, flowers, leaves, stem, and roots, are termed as botanical insecticides. Insecticides of plant origin, unlike synthetic organic insecticides, are safer to use but since they are expensive and lack residual toxicity, their use has been limited in the country.
1) Neem (Azadirachta indica) (As Insecticides)
Perennial tree distributed in tropical, subtropical, semi-arid and arid zones. It poses medicinal, insecticidal, insect repellent, antifeedant, growth regulatory, contains nematicidal and antifungal properties. Neem seed extract contains a number of components such as Azadirachtin, salannin, nimbin, epinimbin nimbidin that gives insecticidal, insect repellent, ovicidal, Antifeedant and growth regulator characters.
Azadiractitin disrupts moulting by antagonizing the insect hormone ecdysone. Azadiractin Acute oral LD50 for rat is 5000mg/kg, Acute dermal for rabbit is >2000mg/kg.
Preparation of Neem Seed Kernel Extract (NSKE 5%):
Take 50 g of powdered neem seed kernels soak it in one litre of water for 8 hours and stir the contents often. Squeeze the soaked material repeatedly for better extraction of the azadirachtin in the aqueous suspension. Filter the contents through a muslin cloth. Make the filtrate to one litre. Add l ml teepol or triton or sandovit or soap water (2%) and spray. Preparation of Neem Cake Suspension Soak one kilogram of neem cake in 5 liters of water for 2 days and filter It through the muslin cloth. Dissolve 200 g of soft soap in the filtrate and make upto 10 L of water before spraying. This controls tobacco cutworm, leaf miners of citrus, groundnut, tomato and beans etc. Dried powder of neem leaves are used against stored grain insect pests.
Prepartion of Neem Cake Suspension
Soak one kilogram of neem cake in 5 liters of water for 2 days and filter It through muslin cloth. Dissolve 200 g of soft soap in the filtrate and make upto 10 L of water before spraying. This controls tobacco cutworm, leaf miners of citrus, groundnut, tomato and beans etc. Dried powder of neem leaves is used against stored grain insect pests.
Leaf extracts showed insecticidal property against, P lutella xylostella,A proaerema modicella; Spodoptera litura etc. Desert locust Schistocerca gregaria avoids feeding on neem leaves. Leaves of Neem are found as attractants to white grub Holotrichia adults. Neem seed/ kernel extract showed insecticidal properties against a number of sucking pest. Neem oil can be used against storage insect pests @ 1 to 2% and field insects @ (0.2 -0.4%, 1 to 2% 5% or 10% neem oil). The Neem products are safer to honey bees, parasitoids, predators. Commercial formulations of neem are available in 10000 ppm;1500 ppm and 300 ppm the market. Some of the neem formulations are Margosan, Neemark, N eemrich, Achook, Bioneem, Neemazal, Neemax, Nimbicidine, V epacide, Margocide ,N eemgold etc
2) Nicotine:
Nicotine is found in the leaves of Nicotiana tabacum and /V.rusticafrom 2%to 14%.Nicotine sulphate has been mainly used as a contact insecticide with marked fumigant action in the control of sucking insect’sviz., aphids, thrips, psyllids, leafminers, and jassids. Nicotine sulphate is more stable and • less volatile. It is a nerve poison being highly toxic when absorbed through the cuticle taken in through the tracheae or when ingested. It affects the ganglion blocking conduction at higher levels, Nicotine sulphate containing 40% alkaloid, is safer and is more convenient to use and the free alkaloid is liberated by the addition of soap lime or ammonium hydroxide to the spray solution.
Dust formulation of nicotine sulphate releases nicotine in the presence of moisture. It is also used in aerosols. Tobacco decoction, useful for controlling aphids, Thrips etc. can be prepared by boiling 1kg of tobacco waste in 101ts of water for 30 minutes or steep it in cold water for a day; Then make it up to 30 litres and add about 90gm of soap, Addition of soap improves wetting, spreading and killing properties. Nicotine does not leave any harmful residue on treated surface. LD5Ofor rat oral- 50-60 trig/kg.
3) Rotenone:
It is extracted from the roots of Derris plant which many contain 4 to 11% rotenone depending on the variety. Though rotenone is reported from 68 species of leguminous plants, principal commercial sources are Derris elliptica D. Malaccensis from Malaysia and Lonchocarupus utilis and D. uruca from S. America. Rotenone occurs in Derris roots (4-9%), Lonchocarpus (8-11%). It is oxidized to non-insecticidal compound in the presence or light and air and hence rotenone residues arc difficult to find after 5 to 10 days in normal sunlight. Insects poisoned with rotenone show a steady decline in oxygen consumption followed by paralysis and deaths. It is very specific being highly toxic to fishes and to most insect species but almost harmless to warm-blooded animals except pigs LD50 to white rat 130 to 1500. Dust or spray containing 0.5 to 1.0 percent and 0.001 to 0.002 percentrotenone are used commercially.
4. Plumbagin
Plumbagin is naturally occurring naphthoquinone of plant origin from the roots of Plumbago europea L (Plumbaginaceae) and named so in 1828 by Bulong d’ Astafort. Blumbagin is known for its medicinal, antifertility, antimicrobial, mulluscicidal, nematicidal and other pharmacological properties on diverse fauna. The yield of plumbagin ranges between 0.5-3.000 per cent on dry weight basis. the elucidation of structure of plumbagin and its synthesis in 1936 led to detailed studies. More recently, its IGR properties viz., inhibitionof chitin synthetase and exdysteroid titres have been demonstrated (Kubo et al., 1982).
The cold alcoholic extracct (5%) of roots of P. zeylanic L was toxic to Euproctis fraterna larvae as contact spray. Contact toxicity of 5% petroleum ether extracts of P. zeylanic root against Spodoptera litura Fab., Dystercus koenigii Fab., Dipaphis erysimi Kalt, Dactynops carthami HRL, Coccinella septumpunctata L was also reported.
5. Pyrethrum:
It is extracted from dried flower heads of Chrysanthemum cinerariaefolium (Asteraceae). The actual chemical ingredients having insecticidal action are identified as five esters. They are Pyrethrin I, Pyrethrin, II, Cinerins I and Cinerin II and Jasmoline, which are predominately found in achenes of flowers from 0.7% to 3%. The esters are derived from the,
Two acids – Chrysanthemic acid and Pyrethric acid
Thre alcohols- Pyretholone, Cinerolone and Jasmolone
Active principles/Esters
Pyrethrin I = Pyrethrolone + Chrysanthemc acid Pyrethrin II = Pyrethrolone +
Pyrethrin II = Pyrethrolone + Pyrethric acid Cinerin I = Cynerolone +
Cinerin I = Cynerolone + Chrysanthemc acid
Cinerin II = Cynerolone + Pyrethric acid
Jasmolin II = Jasmolone + Pyrethric acid
Pyrethrum powder is prepared by grinding the flowers. The powder mixed with a diluent such as a talc or clay is known as pyrethrum dust. It is prepared just before use. Otherwise, it gets deteriorated rapidly. It is also used as emulsions, solutions, and aerosols. Pyrethrum is unstable to light, air moistUre and alkali. The residues deteriorate very rapidly after application. Pyrethrins are powerful contact insecticides but appear to be poor stomach poisons. A characteristic action of Pyrethroid is the rapid paralysis or ‘knock down’ effect and substantial recovery that follow it. This recovery is due to rapid enzymatic detoxification in the insect. To bring about mortality equivalent to knock down effect three times increase in dosage may be required. Compounds such as piperonyl butoxide, propyl isome, and sulfoxide are known to inhibit the detoxication enzyme and increase toxicities of pyrethroids. These synergists are used at 10 parts to 100 part of pyrethroid. LDSO. for white rat oral-200 dermal for rat-1800. Pyrocon E 2/22 (1 part of pyrethrin + 10 parts of piperonyl butoxide) is used for the control of coconut red palm weevil. In household sprays and as a repellent against external parasites of livestock pyrethrum is useful. It is also mixed with grains in storage to protect from stored grain pests. Its use alone or in combination with piperonyl butoxide as food packages has been permitted by the Food and Drug Administration in the U. SA. and no other chemical has been approved.
Properties of Plant origin Insecticides
- Highly unstable in light, moisture, and air.
- Have no residual effect.
- Paralyse by more contact.
- Gains entry through spiracle and cuticle.
- Act on central nervous system.
- Having rapid knock down effect
- Practically no mammalian toxicity.
- Good insecticides against household and cattle pests.