Temperature 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 agricultural ecosystem, reducing many lepidopteran pest incidences. The laboratory strains of T. chilonis was significantly inferior to the ecotypes collected from fields in their parasitisation potential and tolerance to temperature due to continuous exposure to temperature extremes 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 temperature tolerant ecotype for use in pest management programme. 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 temperature in comparison with the laboratory population. The emergence percentage of the parasitoid varied with the ecotypes tested and all the field collected ecotypes recorded increased emergence compared to the laboratory population. At 150 C, the emergence was significantly higher in Chitteri ecotype (83.44%) followed by Arungunam and Amirthapuram ecotype (78.65 and 75.57%). The performance of all the ecotypes were best at 200 C and Chitteri ecotype performed significantly better compared to other ecotypes and the laboratory population with an adult emergence of 95.66 per cent. It was followed by Arungunam ecotype (88.65%) at 200 C. While the laboratory population and other ecotypes failed to develop at 350 C, Chitteri and Arungunam ecotypes were able to develop with 9.66 and 7.25 per cent adult emergence from the parasitised eggs.