Heat treatment of empty storage bins and grain-processing facilities: factors influencing efficacy against adults of the red flour beetle, Tribolium castaneum (Herbst)

Abstract

Heat treatment, a more than 100-year-old technology, involves raising the ambient temperature of a an empty bins/storage space or a clean gran-processing facility to 50-60°C for 24 h or less to kill stored-product insects. Heat treatment is an environmentally benign and a safer alternative to chemical insecticides. The studies reported here were conducted to determine the effect of short-term exposure to sub-lethal temperatures on adults of Tribolium castaneum (Herbst) and their subsequent susceptibility to temperatures of 50 and 55°C for 60 and 15 min, respectively; to determine the effect of rearing T. castaneum at select elevated temperatures for 10 generations on their subsequent susceptibility to temperatures of 50 and 55°C; to determine the effects of age and sex on susceptibility of T. castaneum adults to 50 and 55°C; and to determine the effectiveness of a diatomaceous earth (DE) formulation at several elevated temperatures below 50°C on the mortality of T. castaneum adults. Results of the studies showed that short-term exposure between 24 and 72 h, to sub-lethal temperatures (32, 36, and 40°C) only increased survival for insects acclimated to 32°C. Acclimation at 36 and 40°C resulted in higher mortality after exposure for 24, 48, and 72 h at 50 and 55°C. Rearing insects at 32 and 36°C for 10 generations resulted in the highest survival of adults at 50°C. However, when adults reared at 32°C were exposed during heat treatment of Hal Ross Flour Mill, the adults were least susceptible to dynamically changing temperatures over time. Female T. castaneum adults were more heat tolerant than males, and adults 1 d post-emergence were the most heat tolerant when exposed to 55°C for 15 minutes compared with adults aged 7-42 d. The efficacy of DE was enhanced at higher constant temperatures, which can lessen energy inputs in order to obtain a complete kill of insects when temperatures do not reach 50°C or greater. Given the changing climate, it is very useful for researchers to understand the implications of increasing temperatures on the heat tolerance of insects.