Development of Chlorpyriphos Tolerant Strain of Trichogramma chilonis Ishii and its Efficacy against Helicoverpa armigera

Development of chlorpyriphos tolerant strain of Trichogramma chilonis was attempted against H. armigera. For the chlorpyriphos tolerance, superior strain of T. chilonis was subjected to selection pressure. Laboratory selection was started from the 1/10^th of field recommended dose and ended with 1/4^th of field dose of chlorpyriphos. T. chilonis took seven generations to develop tolerance against 1/10^th of field dose, eight generations against 1/8^th, twenty three generations against 1/6^th of field dose and thirty two generations against 1/4^th of field recommended dose. At each 5^th generation strain was tested for consistency and at F₇₀ % parasitization and % emergence by tolerant strain were increased up to 83.3 and 79.0%, respectively, whereas 15.6 and 19.0% parasitization and adult emergence were given by susceptible strain at 1/4^th of the field dose of chlorpyriphos whereas, only 64.3% parasitization and 57.6% emergence were recorded by tolerant strain as compared to 15.0% parasitization and 17.6% emergence by susceptible strain at 5^th generation at 1/10^th of field recommended dose of chlorpyriphos. After the laboratory selection, the tolerant T. chilonis strain was tested at each tolerance level for parasitism and emergence from the eggs of H. armigera. 1/10^th of field dose of chlorpyriphos i.e. 0.006% tolerant strains gave 28.0% parasitization and 27.6% adult emergence from the eggs of H. armigera, whereas, susceptible strain had 9.6% parasitization and 10.3% adult emergence. But at 1/4^th of field dose of chlorpyriphos i.e. 0.015% tolerant strain was resulted 49.3% parasitization and 51.0% adult emergence at fielddose of chlorpyriphos as compared to 14.6% parasitization and 15.0% adult emergence by susceptible strains.