The effect of grain moisture content and temperature on the efficacy of diatomaceous earths from different geographical locations against stored-product beetles

Source of diatomaceous earth (DE), insect species, grain moisture content, temperature, method of application and duration of exposure were all factor s that influenced the mortality of stored-product insects. In all tests, re gardless of the insect species, or source of DE, the lower the moisture con tent of grain, the greater the mortality. DEs from different geographical l ocations had different efficacies. The ranking of the different DEs remaine d similar at different moisture-temperature combinations. However, the mort ality response with respect to moisture content did change among DEs from d ifferent sources for Sitophilus oryzae (L.), but not for Tribolium castaneu m (Herbst). Of all the insects tested, Cryptolestes ferrugineus (Stephens) was the most sensitive to DE. Oryzaephilus surinamensis (L.) and S. oryzae were more to lerant than C. ferrugineus. Rhyzopertha dominica (F.) and T. castaneum were the most tolerant species tested. Applying DE as a dust was more effective than applying DE as an aqueous spray. For C. ferrugineus, lower temperatures reduced DE efficacy. The opposite wa s true for T. castaneum, as lower temperatures increased efficacy for most DEs tested. For S. oryzae some DEs had increased efficacy with lower temper atures and others had decreased efficacy with lower temperatures. Published by Elsevier Science Ltd.