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1. 1
Factors affecting toxicity of
insecticides
Submitted to Presented by
Dr. G.S. Panduranga, S.Archana Devi,
Assistant professor, TAM/2019/024.
Dept of Entomology.

2. contents
2
1. Introduction
2. Physico chemical factors
3. Plant factors
4. Soil factors
5. Insect factors

3. 3
Insecticide toxicity

4. 4

5. Physico Chemical Factors
Plant Factors
Soil Factors
Environmental Factors
Insect Factors
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1
2
3
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6. Physico chemical factors
⬩ Surface on which toxicant is applied
⬩ Physical state of the toxicant.
⬩ Gas, Solid &liquid.
⬩ Effective dust particle size-10µ
⬩ Hardness,Activation,water adsorbing
capacity
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7. ⬩ Spray supplemnts (Spreaders and wetters)
⬩ Emulsifiers and Dispersing agents.
⬩ Optimum droplet size is 20 µ.
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8. ⬩ Compound
⬩ Chemical stability
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 Primary compound
 Derived compounds
 Metabolites
 structural stability
 voltalization
 solubility

9. Primary compound
⬩ Inherent toxicity
⬩ Toxicity of tetraethyl pyrophosphate (TEPP) is
approximately 588 times greater than that of pyrethrum
extract.
⬩ Nicotine is about 103 times more toxic than difenphos.
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10. Derived compounds
⬩ chemical changes
⬩ During storage
⬩ Exposure to UV light, plant enzymes, or soil
microorganisms
⬩ Differ chemically and toxicologically
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11. 11

12. Metabolites
⬩ Biotransformation
⬩ Olefine-higher attraction or affinity.
⬩ Clothiandin- Accumulation at higher concentrations .
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More water soluble
+ More Active

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14. Structural stability
⬩ Basic structure is fundamental
⬩ Rapid break down of a readily metabolizable pesticide.
⬩ stable chemical –More persistent.
⬩ Aldrin
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Dieldrin
46
mg/kg
38mg
/kg

15. Volatilization
⬩ High vapor-pressure values –more volatile.
⬩ Move off-site and cause injury.
Solubility
⬩ Highly soluble Pesticides - surface runoff.
⬩ Pass down through the soil in large quantities.
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16. Dosage
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17. Synergists
⬩ Active moiety Methylendioxyphenyl (MDP).
⬩ Sesamin , Sesamolin and piperonyl butoxide .
⬩ MGK 264 –Pyrethroids and rotenone.
⬩ Inhibition of cytochrome -450 monoxygenase.
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18. 18
Plant factors

19. Plant species
⬩ structure of plant
structural features- distribution, retention and uptake
(1)plant form (erect, spreading, prostrate)
(2) leaf shape (broad, narrow, large, short, linear)
(3) leaf position and density (horizontal, upright,
pendulous)
(4) leaf surface and margins (hairy, waxy, sculptured).
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20. 20
Retention
Wettability

21. PLANT METABOLIC ACTIVITY
⬩ Rate of uptake:
⬩ Influenced by environmental factors.
⬩ Penetration – higher in pea plants grown in dark.
⬩ Uptake of O.P insecticides-enhanced if cuticle is kept
moist.
⬩ More at field capacity.
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22. 22
Soil Factors

23. Soil type
⬩ DDT was less effective in soils high in clay or organic
content (Lange and Carlson ,1956).
⬩ organic content of the soil retarded the insecticidal action
of chlordane. (Fleming et al .,1962)
⬩ The relationship between organic content and insecticide
toxicity appears to be curvilinear with heptachlor, DDT.
⬩ Sandy > Loam > Clay
⬩ Diazinon, disulfoton, parathion, and Nemacide-
Inactivation in mineral soils. 23

24. 24

25. Soil moisture
⬩ Ethylene dibromide sorption
⬩ Fumigant toxicity of aldrin.
⬩ Dieldrin > DDT> heptachlor> aldrin > chlordane.
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In relative humidity

26. 26
Annual review of entomology .17:177-198

27. Soil temperature
.
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28. Mechanisms of insecticide inactivation in soil
⬩ Toxicity of an insecticide - insecticide adsorption
⬩ Diazinon-dry sandy soil, Heptachlor-dry clay soil,
⬩ Nemacide-light and heavy mineral soils.
⬩ Moist soil - Desorption
⬩ Soil temperature - Desorption
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29. 29
Environmental factors

30. Temperature
⬩ Organophosphorus, carbamate and neonicotinoid insecticides-
+ve temperature coefficient .
Toxicity of thiamethoxam to Aphanostigma piri 1.86 fold 30°C
when compared with the toxicity at 20°C (Ma et al., 2010).
⬩ Pyrethroids:-ve temperature coefficient.
⬩ At 24°C,toxicity of Lambda-cyhalothrin against Ostrinia
nubilalis increased by 13.6-fold compared to the temperature of
35°C (MusserandShelton, 2005).
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34. Precipitation
⬩ Washes surface residues
⬩ in soil moisture .
⬩ Favours microbial activity.
⬩ Amount, Intensity, Insecticide activity &target insect.
⬩ EC > SC&(F) > WP &(G) >Dusts.
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35. Radiation
⬩ UV-light :Break down of Insecticides.
⬩ Pyrethrins –More succeptible.
⬩ ses the volatilization
⬩ uptake
Wind:
⬩ Insecticide drift.
⬩ Uptake of insecticides.
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36. 36
Insect Factors

37. 37
Insecticide

38. Detoxification
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39. Storage of toxicant :
⬩ Inert storage
⬩ Schradan on female American cockroach.
Age:
⬩ Inactive stages are less susceptible.
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40. 40

41. Sex :
Female insects are more tolerant.
Food:
Variegated cutworm larvae fed peppermint leaves –
Carbaryl, acephate , methomyl & Malathion than larvae
fed on snap bean leaves.
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42. ⬩ Fall army worm larvae fed on corn leaves became less
susceptible to Methomyl, Acephate ,diazinon, trichlorofan,
monocrotophos, permethrin and cypermethrin than fed on
soyabean leaves.
⬩ Tobacco bud worm –DDT-Ascorbic acid
Population density:
⬩ Susceptibility of adult granary weevils to crabon disulfide
decreased slightly as population size increased.
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43. References
⬩ Insecticides (Toxicology and use) –H.C.L.Gupta.
⬩ The toxicology and bio chemistry of insecticides by Simon j.u.
⬩ Harris, C.R.1972. Factors influencing the effectiveness of
soil insecticides. Annu. Rev. Entomol.
⬩ Welling, W.1977. Dynamic aspects of insect -insecticide
interactions. Ann. Rev. Entomol. 22:53-78.
⬩ Encyclopedia of Entomology by John L.Capinera.
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