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 degrees C, 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 degrees C, 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.