Abstract
This study evaluated the influence of temperature and relative humidity (RH) on the insecticidal effect of diatomaceous earth (DE) at two concentrations, 500 and 1000 ppm, on wheat, for the control of Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae), Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). These bioassays were carried out in all combinations of four temperature levels (15, 20, 25, and 30 °C), and two relative humidity levels (55 and 75%). Cryptolestes ferrugineus and O. surinamensis were found to be much more susceptible to the DE-treated wheat than T. confusum, but the increase of the DE dose increased the mortality level for all three species. Although the increase of temperature and the decrease of RH increased insect mortality in some of the combinations tested, the reverse was observed in some treatments, suggesting that there are considerable differential effects of these factors in DE efficacy. The increase of insect exposure from 1 to 21 days notably increased insect mortality, suggesting that exposure is a critical factor that may alleviate possible differential effects of certain abiotic conditions. The results of the present work provide data that illustrate the viability of the utilization of DE in stored product protection, as alternatives to chemical control methods.
Highlights
Diatomaceous earths (DEs) are promising alternatives over the use of traditional insecticides that are currently in use in stored product protection
Mortality of C. ferrugineus adults at 55% relative humidity (RH) was comparable for all temperatures, and mostly depended on the DE dose (Table 2)
At the 21-d exposure, on wheat treated with 1000 ppm, the increase of temperature decreased mortality
Summary
Diatomaceous earths (DEs) are promising alternatives over the use of traditional insecticides that are currently in use in stored product protection. This research has shown that the application of DE can be effective on a wide range of conditions, either as a grain protectant, i.e., through admixture with the grains, or as a surface treatment, i.e., through applications in different types of surfaces in food storage and processing facilities. Between these two ways of application, the use of DEs through direct application with the grains has been by far the most thoroughly studied scenario [4,5,6]. Arthur [13] found that the insecticidal effect of the pyrethroid deltamethrin, which is one of the most widely used grain protectants globally, is negatively affected by the increase of temperature, a parameter that should be seriously taken into account in real-world applications with these insecticides
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