Effect of temperature and relative humidity on diatomaceous earth treated Callosobruchus maculatus (F.) and Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae)

Adults of Callosobruchus maculatus (F.) and Acanthoscelides obtectus (Say) were exposed to the diatomaceous earth Fossil-Shield (R) on treated mungbeans Vigna radiato (L.) and common beans Phaseolus vulgaris (L.) at rates of 1020 mg/kg and 1080 mg/kg, respectively. Diatomaceous-earth-treated bruchids were held at 20 degrees C, 25 degrees C, 30 degrees C, 35 degrees C, and 43%, 52%, 64%, 75% and 84% relative humidity, respectively. Mortality of C. maculatus and A. obtectus generally increased as temperature increased, but the reverse was true for relative humidity. There was no obvious difference between insect mortalities at 25 degrees C and 30 degrees C across the range of relative humidities of 52-75%. The interaction between temperature and relative humidity had little effect on the mortality of C. maculatus, but did influence levels of control of A. obtectus. Also, A. obtectus was less susceptible to Fossil-Shield (R) than was C. maculatus. As for many stored-product insect pests, temperatures between 25 degrees C and 30 degrees C are physiologically optimal for bruchids, but 35 degrees C is close to the maximum tolerable temperature. At 20 degrees C, most of the tropical and subtropical stored-product insects show reduced activity, so the amount of lethal dust picked up by insects becomes very small.