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

Abstract

Source of diatomaceous earth (DE), insect species, grain moisture content, temperature, method of application and duration of exposure were all factors that influenced the mortality of stored-product insects. In all tests, regardless of the insect species, or source of DE, the lower the moisture content of grain, the greater the mortality. DEs from different geographical locations had different efficacies. The ranking of the different DEs remained similar at different moisture–temperature combinations. However, the mortality response with respect to moisture content did change among DEs from different sources for Sitophilus oryzae (L.), but not for Tribolium castaneum (Herbst). Of all the insects tested, Cryptolestes ferrugineus (Stephens) was the most sensitive to DE. Oryzaephilus surinamensis (L.) and S. oryzae were more tolerant 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 was true for T. castaneum, as lower temperatures increased efficacy for most DEs tested. For S. oryzae some DEs had increased efficacy with lower temperatures and others had decreased efficacy with lower temperatures.