The degradation pattern of soil applied insecticides was studied in the field during main (April - June) and autumn (July - September) seasons. Samples were collected from potato field treated with carbofuran (1.0 kg a.i./ha), quinalphos (1.25 kg a.i./ha) and phorate (2.5 kg a.i./ha),the commonly used insecticides to combat the major soil pests like cutworms Agrotis ipsilon (Hfn), white grubs Holotrichia sp., tuber moth Pthorimaea operculella(Zeller) and golden cyst nematode Globodera rostochinensis (Wollenweber). The rate of initial dissipation in carbofuran was 32.0 per cent in first 15 days of application in main season and up to 51.4 per cent at 30 days of application in autumn. A 70.0 per cent reduction in the initial deposit was observed for quinalphos residues up to 30 days in both seasons. The initial loss is more in phorate which declined to an extent of >80.0 per cent on day 15 in both seasons. For all the three insecticides studied the residues reached below detectable limit on 90 days after application. The respective half life values for carbofuran, quinalphos and phorate were 15.06, 14.14 and 6.99 during main season and 15.97, 12.67 and 14.17 days during autumn seasons. The degradation pattern followed first order kinetics for all three insecticides applied during both season.
The residue of quinalphos (Ekalux) 20 AF and 25 EC formulations were determined in notton seed and lint. The residue in the lint samples from plots treated with the highest dose varied from below detectable level (BDL) to 0.06 ppm in the first picking and 0.02 to 0.09 ppm in the third picking. At lower doses the residue were BDL. Except in one seed samplp from plots treated with the highest dose of quinalphos 25 EC, the residue were BDL ii all samples of first as well as third pickings.
The development of resistance has limited the application of single insecticides and resort to tank mixtures. Mixing of two or more insecticides is very common among the Indian farmers though not recommended. Pest populations to be controlled should be susceptible or have low levels of resistance to each insecticide used in the mixture. In India more than 85% of the combination products have synthetic pyrethroids as one of the components, to which the cotton bollworm (Helicoverpa armigera) has developed very high level of resistance. Hence, sustaining the efficacy of the combination products is questionable in the near future. Combination products if permitted will be used as a matter of routine and there may be development of multiple resistant individuals. If there is any need arises, then mixtures can be considered for one time remedy. Testing of the combination products can be taken for generating data and may be recommended in India after evaluating the development of resistance. Scope and considerations for proper use of insecticide mixtures with special reference to insecticide resistance management in India have been discussed in this review.
Observations on the incidence of mealybug, Paracoccus marginatus Williams and Granara de Willink and spider and ants associated with it were recorded in 10 papaya fields each (total of 30 fields) falling in three categories viz. 1) Abandoned and severely infested fields released with parasitoid Acerophagus papayae , 2) Infested but yielding fields released with A. papayae. and 3) Fields with 2–4 months old crop without parasite release in Tamil Nadu. The P. marginatus incidence was reduced to an extent of 7–33 per cent with very low intensity in parasitoid released fields. Six species of spiders viz. Clubiona spp. crab spider , Thomisus spp., Jumping spider Phidippus sp., Plexippus sp. , Araneus sp. wolf spider , Lycosa pseudoannulata were found and the most predominant one was Araneus sp. Nine species of coccinellids, viz. Brumoides suturalis (Fabricius) , Cheilomenes sexmaculata (Fabricius), Coccinella septumpunctata Linnaeus, Coccinella nigrita Fabricus , Cryptolaemus montrouzieri Mulsant, Hippodamia variegata (Goeze), Hyperaspis maindroni Sicard, Nephus regularis Sicard and Scymnus coccivora Ayyar recorded from the fields. Two species of chrysopids, Chrysoperla zastrowi silemi (carnea) and Mallada sp. were observed. Parasitoids A. papayae and Torymus sp. (Torymidae) only were found. Four species of ants viz., Camponotus compressus (Fabricius), Camponotus sericeus (Fabricius), Camponotus parius Emery and Tapinoma melanocephalum (Fabricius) were found to be associated with mealybug. Avoidance of insecticide spraying resulted in the appearance of notable number of biocontrol organisms in papaya fields in Tamil Nadu.
The base line susceptibility response to five commonly used insecticides viz., endosulfan, chlorpyrifos, profenofos, fenvalerate and deltamethrin in Spodoptera litura (Fabricius) field population from rainfed growing groundnut area of Madurai district (Alagarkovil) in Tamil Nadu, was determined by topical application. LD50(s) were calculated as 0.7628, 0.0355, 0.3710, 0.0672 and 0.0647 ppm for endosulfan, chlorpyrifos, profenofos, fenvalerate and deltamethrin, respectively.
The joint action between nucleopolyhedrovirus (HearNPV) and synthetic pyrethroids at sub lethal concentration against third instar larvae of Helicoverpa armigera oo nifferent tosts (cotton leaves, cottoo nquares, cottoo nolls, bhendi fruits and redgram pods) were investigated. The joint application of HearNPV + pyrethroids at LC25 + LC25 revealed synergistic interaction as the combined application on different hosts showed 9.27 - 27.68 and 21.68–40.91% more than the expected mortality at LC50 of HearNPV alone and LC50 of pyrethroids alone, respecttvely.
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