Pesticide Tolerance in the Five Field Strains of Trichogramma chilonis from Northern Districts of Tamil Nadu, India

Abstract

The egg parasitoid, Trichogramma chilonis is a potential egg parasitoid in the sugarcane, reducing early shoot borer and internode borer population. The laboratory strains of T. chilonis was significantly inferior to the ecotypes collected from fields in their tolerance to insecticide due to continuous exposure to insecticides in the field. Hence, a study was undertaken to evaluate the laboratory reared strain of T. chilonis with that of other ecotypes to identify a pesticide tolerant ecotype for use in pest management by augmentative release. Five ecotypes of T. chilonis were collected from farmer's fields on sugarcane and citrus using sentinel egg technique by exposing egg cards of Corcyra cephalonica, mass reared on C. cephalonica for three successive generations and tested for their relative tolerance to insecticides in comparison with the laboratory strain.  Significantly higher level of parasitisation (50.59, 45.32 and 60.45 %) by Arungunam ecotype was observed on eggs sprayed with Imidacloprid 70 WS, Thiomethoxam 75 SG and Flubendiamide 20% WG respectively before exposing to the parasitoid. The Chitteri ecotype was found next in order of tolerance to the insecticides Imidacloprid 70 WS, Thiomethoxam 75 SG and Flubendiamide 20% WG (45.00, 41.23 and 58.23 % respectively). The adult emergence was not found to be affected much by the insecticides sprayed before parasitisation. Varying degrees of insecticide toxicity against different ecotypes of T. chilonis inside host eggs was observed and Arungunam ecotype showed more tolerance to the insecticides tested with,71.28, 53.46  and 81.67 per cent adult emergence respectively from parasitised eggs sprayed with Imidacloprid 70 WS, Thiomethoxam 75 SG and Flubendiamide 20% WG. Among the insecticide tested, Flubendiamide was least toxic to the parasitoid developing with in the host egg and Thiomethoxam was found to be more toxic with nearly 50 per cent reduction in the adult emergence.