Genetic Improvement of Egg Parasitoid Trichogramma chilonis Ishii for Combined Tolerance to Multiple Insecticides and High Temperature

A strain of Trichogramma chilonis Ishii, an effective parasitoid of lepidopteran pests was developed for tolerance to three major groups of insecticides, i. e., endosulfan (organochlorine), monocrotophos (organophosphate) and fenvalerate (synthetic pyrethroid) and to high temperature (32-38°C) through selection. After 81 generations of selection, there was an increase in parasitism from 35% to 90-95% and decrease in mortality from 100% to 57-70% after 6h of constant exposure to three insecticides and high temperature. Interestingly 46.8 and 2.9 fold increase in tolerance was observed in males compared to 18.5 and 1.3 fold increase in females of MITT (multiple-insecticide and temperature tolerant) strain when exposed to endosulfan and fenvalerate sprays, respectively, while in case of monocrotophos, females and males were 465-fold and 25-fold more tolerant, respectively, than susceptible strain. At higher temperatures of 40 and 45°C, the per cent mortality of tolerant adults was 0.0 and 9.2%, respectively, compared to 59.7 and 96.1% in susceptible population after 6h of exposure at these temperatures. At high variable temperature (32-38°C), per cent mortality in MITT was 57.1 compared to 98.5% in susceptible population after 24h of constant exposure. The mean per cent parasitism at 32°C, 36°C, 38°C and at variable temperature of 32-38°C was significantly higher in tolerant strain (46.7, 45.0, 18.3 and 63.3%) compared to susceptible strain (54.0, 6.7, 0.0 and 0.0%), respectively. These studies suggest that the improved strain of T. chilonis will provide effective control of the pest even at harsh climatic conditions and under high insecticide pressure in different economically important crops.