Residual toxicity of some insecticides to the adults of Trichogramma chilonis under both laboratory and field conditions
Investigations were carried out to assess the residual toxicity of some insecticides viz., endosulfan, imidacloprid, spinosad, triazophos, thiodicarb, novaluron and azadirachtin on adult survival of Trichogramma chilonis Ishii under laboratory and field conditions. Per cent adult mortality was observed after exposing the adults to 0, 1, 3, 5, 7, 10 and 15 days of preparation of insecticide film in glass vials and field sprayed tomato leaves. In laboratory conditions only novaluron (22 % mortality) was found to be safe while all the other insecticides remained toxic even upto 15 days of preparation of film causing 100 per cent mortality. Residual toxicity studies under field conditions showed that all the insecticides except novaluron caused 100 per cent mortality even on one day old residues whereas novaluron remained safe even on fresh insecticide residue and remained so up to 15 days after treatment. By third day, endosulfan, imidacloprid and azadirachtin showed decreased adult mortality resulting in 57.3, 68.7 and 61.3 per cent, respectively, but still remained higher than control (5.3%) while spinosad, thiodicarb and triazophos still remained highly toxic resulting in 100 per cent mortality. From the fifth day onwards all the insecticides showed a consistent decrease in toxicity as observed from the decreasing adult mortality as the age of the insecticide residues tested increased.