Persistent toxicity of some insecticides to Trichogramma Chilonis and T. japonicum on Paddy

Commercial formulation of lindane (0.1%); endosulfan, quinalphos, monocrotophos (each at 0.05%); cypermethrin, deltamethrin and fluvalinate (each at 0.005%) were sprayed on paddy crop (cv. Jaya) 30 days after transplanting. Paddy leaves were collected from each plot at regular interval starting from 1 hour after spraying and kept in glass tubes in the laboratory for toxicity study. Laboratory reared 10 adult female parasites were released in each tube. The insecticides differed considerably in their persistency, period of efficacy and index of persistent toxicity (PT value) towards both the parasitoids. Of all the insecticides, lindane showed highest persistency followed by cypermethrin irrespective of the parasitoid species. Fluvalinate recorded longer persistency in case of T. japonicum as compared to T. chilonis whereas average residual toxicity was reverse with deltamethrin. Considering the retention period of toxic residues, both the parasitoids could be released in the crop ecosystem after 4–5 days of fluvalinate spray; 6–7 days after cypermethrin and quinalphos spray and 7–8 days of lindane spray.