EFFECT OF ABIOTIC FACTORS ON THE EFFICACY OF Beauveria bassiana AND DIATOMACEOUS EARTH AGAINST Rhyzopertha dominica (F.)

Current bioassays were performed to assess insecticidal efficacy of diatomaceous earth (DE) Concern® and Beauveria bassiana under various levels of temperature (25, 30 and 35°C) and relative humidity (RH; 45, 60 and 75%) against Rhyzopertha dominica. Three dose rates of DE (200, 400 and 800ppm) and B. bassiana (1x108, 1.5x108 and 2x108 spores/kg grain) were applied on wheat grains and mortality was noticed after 7, 14 and 21 d, whereas adult progeny emergence was observed 60 d of post exposure. The data analyses had shown diversified results regarding test insect susceptibility. Regarding DE, increase of temperature and decrease of RH significantly increased adult mortality. Maximum mortality of 74.33% was assessed with a highest tested dose of 800ppm after 21 d exposure at 35°C and 45% RH, progeny development was also greatly suppressed at same abiotic conditions. For B. bassiana, efficacy was highly dependent on temperature and RH, as lower level of temperature (25°C) and moderate RH (60%) showed maximum mortality of 82.5% with dose rate of 2x108 spores/kg grains after 21 d. Emergence of offspring in fungus treated grains was highly suppressed at 25°C with combination of both 45% and 60% RH whereas at 30° and 35°C significant reduction of progeny was noticed only with 45% RH. The present study divulge that in current scenario of climate change, that alter the patterns of environment, abiotic factors specifically temperature and humidity should be seriously considered when planning an IPM strategy based on the application of B. bassiana and DE Concern®.