Persistence and efficacy of diatomaceous earth against stored product insects in semi-field trials

Abstract

The utilization of inert dusts, such as diatomaceous earths (DEs), has been successfully evaluated against a wide range of major stored-product pest species, as an environmentally friendly alternative to conventional insecticides, emphasizing further their prominent position in Integrated Pest Management (IPM) protocols. However, the majority of the published research about the DEs’ insecticidal efficacy has been conducted under laboratory conditions in small-scale samples (usually in small vials containing few grams of grains) and against specific insect species, while field and semi-field applications for the same purpose are disproportionally few. The objective of this work was to evaluate the insecticidal activity of a commercial DE formulation against stored product species that either artificially or naturally infested hard wheat, under “real-world” storage conditions. For this purpose, DE doses of 0 (control), 500 and 1000 ppm were applied in a series of lots of 20 kg of hard wheat stored in polypropylene woven bags and kept from August to December in a storage facility in Central Greece. According to our results, even the lower DE dose significantly suppressed the insect populations of Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Trogoderma granarium Everts (Coleoptera: Dermestidae) that were artificially added in the wheat bags but also of five other insect pest species that were found in the commodity, based on weekly monitoring via probe traps or grain samples. Rhyzopertha dominica, T. granarium and S. zeamais were the most numerous species found, while T. granarium was the most frequently sampled species. In general, the probe traps were more sensitive to captures, as compared to the grain samples. The evaluation of the grain quality (bulk density, insect damaged kernels) throughout the trials indicated higher insect infestations in the untreated wheat as compared to the treated one. At the same time, grain bulk density was lower in the treated than in the untreated wheat. We conclude that DE applications can effectively suppress the populations of a wide range of stored insect species, offering a prolonged protection under a wide range of environmental conditions.