Immediate and delayed mortality of Oryzaephilus surinamensis (L.) exposed on wheat treated with diatomaceous earth:: effects of temperature, relative humidity, and exposure interval

Adult Oryzaephilus surinamensis (L.), the sawtoothed grain beetle, were exposed for 4-72 h on wheat treated with diatomaceous earth (Protect-It(TM)), then removed and held for 1 week on untreated wheat. Beetles were exposed and held at 22, 27, and 32 degreesC, 40, 57, and 75% r.h. (nine combinations). Mortality after the initial exposures increased as exposure interval and temperature increased, but humidity effects were inconsistent with temperature. Mortality after the one-week holding period was greater than initial mortality, and also increased as the original exposure interval and the temperature increased. At 22 and 27 degreesC, mortality of beetles exposed from 4 to 24 h at 75% r.h. was significantly lower than mortality of beetles exposed for the same time intervals at 40 and 57% r.h. Nearly all of the beetles exposed for 72 h at all three relative humidities were dead after 1 week. The relationship between exposure interval and mortality was described by sigmoidal and linear regression for both the initial mortality and mortality 1 week after being transferred to untreated wheat. Results indicate that O. surinamensis is susceptible to the Protect-It(TM) formulation of diatomaceous earth, and will continue to suffer from the effects of exposure even after they are removed from the treated environment. Published by Elsevier Science Ltd.