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Insecticides

Insecticides. Introduction. Used to kill insects . Control of arthropod borne disease by insecticides is one of the greatest triumph of public health. Classification.

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Insecticides

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  1. Insecticides

  2. Introduction • Used to kill insects . • Control of arthropod borne disease by insecticides is one of the greatest triumph of public health .

  3. Classification • Contact poison : pyrethrum, DDT, HCH, lindane, malathion, fenthion, methyl parathion, abate, carbaryl, propoxur, resmethrin, bioresmethrin • Stomach poison : paris green, sodium fluoride • Fumigants : hydrogen cyanide, sulphur dioxide

  4. Classification • Contact poison – kills insect by contact eg. Pyrethrum, DDT, dieldrin • Stomach poison – when ingested causes the death of insect eg. Paris green , sodium fluoride • Fumigants – gives off vapour which have lethal effect on the insects eg. Sulphur dioxide.

  5. Insecticides available for vector control • Group 1: – organochlorinecompounds : DDT, HCH (BHC) , dieldrin, chlordane, methoxychlor . • Group 2:- organophosphoruscompounds: malathion , fenthion, chlorpyrifos, abate • Group 3 :- carbamates : propoxur , carbaryl

  6. DDT • DDT :– Dichoro-diphenyl- tricholoroethane • First synthesised in 1874 by German chemist, Ziedler. • Properties :- white amorphous powder , insoluble in water but dissolves in most organic solvents . • DDT contains 70-80 % of para-para isomer , active fraction of DDT.

  7. Continued…. b) Action :- Acts on nervous system of insects Permeates into body through cuticle Dissolves in waxy covering of feet Paralysis of legs and wings Convulsions Death The residual action of DDT last long as 18 months .

  8. Continued…. c) Application :- applies as a dosage of 100-200 mg. per sq foot area. • Formulation of choice is 5 per cent suspension of DDT , when sprayed at rate of 1 gallon over an area of 1000 sq . feet , gives dosage of 200 mg . Per sq ft.

  9. HCH • HCH (BHC) :- • Benzene hexachloride/ Hexa chlorocyclo- hexane / gammexane/ hexidol • Synthesized in 1825 by Michael Faraday. • Properties :- white or chocolate coloured powder with a musty smell . • Irritates eyes , nose and skin • Gamma isomer is most active constituent .

  10. HCH • Technical HCH :– 13 – 16% of gamma isomer. • Pure HCH :- 99% of gamma isomer called as Lindane / gamma HCH. • HCH is slightly volatile . b) Action :- kills insects by direct contact . • Residual action is shorter duration , upto 3 months • Kills by vapour also .

  11. HCH c) Application :- dosage of 25 to 50 mg of gamma HCH per sq ft. is recommended .

  12. Malathion • Malathion :- • Yellow or clear brown liquid with unpleasant smell. • Used in doses of 100- 200 mg.oer sq ft.every 3 months. • It is widely used for killing adult mosquitoes to prevent dengue hemorrhagic fever, and mosquito- borne encephalitis epidemics.

  13. Abate • Abate :- Temephos • Brown viscous liquid , soluble in petroleum solvents. • Extensively used in India for control of A. stephensi in wells and in domestic water containers with dosage 1.0 ppm.

  14. Fenthion • Fenthion :- Baytex • Brown liquid smells as garlic . • Insoluble in water . • Dosage for residual sprays is 100 mg per sq ft. • As a larvicide it is powerful . • Highly effective in controlling larvae of C. fatigans at rate of 1 ppm.

  15. Pyrethrum • Pyrethrum :- • Insecticides of vegetable origin. • Extracted from flowers of Chrysanthemum cinerariafolium . • Properties :- flower contains 4 active principles- Pyrethrins I and II , Cinerins I and II , all nerve poisons . • It is an excellent space spray , ready to spray contain 0.1 % of pyrethrins .

  16. Pyrethrum b) Application :- sprayed at the rate of ½ to 1 oz . Of spray solution per 1,000 cu ft of space. • While spraying , fine atomization is necessary and the doors and windows should kept closed for ½ hours after spraying .

  17. Pyrethrum and DDT • Pyrethrum and DDT:- added for synergistic action . • The standard reference aerosol recommended by WHO consist – • Pyrethrum extract (25% pyrethrins ) , 1.6 % • DDT technical – 3% to be dispersed at the rate of 10 g per 1,000 cu ft of space in the treatment of aircraft. About 1/3rd of doses , 3.3 g per 1,000 cu ft used for routine treatment of dwellings .

  18. Paris Green :- • copper aceto-arsenite • Emerald green microcrystalline powder ,insoluble in water but soluble in ammonia and concentrated acids. • Its an stomach poison . • Was extensively used in control of anopheline larvae . • Responsible for eradication of A. gambiae from Brazil in 1940 .

  19. Insecticide Resistance • WHO definition :- “ The development of an ability in strain of insects to tolerate doses of toxicants which would prove lethal to the majority of individuals in normal population of the same species”. • Resistance is due to biochemical and genetic factors .

  20. Insecticide Resistance • Knowledge important –proper selection of insecticide • Organo-chlorine insecticide resistance: DDT and analogues, HCH-dieldrin group • Double resistance

  21. Possible ways of avoiding development of insecticide resistance in field • Avoid indiscriminate use of insecticides • Avoid use of insecticides that simultaneously select resistance to other chemically related insecticides. • Avoid use of insecticides that induce development of more than one type of resistance mechanism of broad spectrum of resistance. • Avoid use of the same insecticide both against adults and larvae. • Use of non chemical control methods, e.g. biopesticides, larvivorous fish. • Use of synergist with insecticides to reduce physiological resistance.

  22. Toxicity of Insecticides • Organo-chlorine compounds :- • DDT least toxic – lethal dose 250 mg/kg/body weight • Gamma HCH is twice as toxic as DDT , where as dieldrin is 5 to 8 times toxic . • Dieldrin poisoning is more frequently as it is absorbed through skin. • Treatment :- Barbiturates (phenobarbitone), stomach washouts , purgatives .

  23. Organophosphorus compounds and Carbamates • Interfere with mechanism of transmission of nerve impulse • Cholinestraseinhibitors – accumulation of acetyl choline • Signs and symptoms – headache , giddiness , apprehensions , restlessness , cold sweating salivation , uncontrolled urination and defecation , unconsciousness , ataxia and paralysis of respiratory centre.

  24. Organophosphorus compounds and Carbamates • Treatment :- • Specific antidote – Atropine • Doses 1 to 2 mg IM and repeated if necessary at 30 min interval.

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