Laboratory bioassay and dose variation of diatomaceous earth surface treatments

摘要

Diatomaceous earth (DE) can be used as a grain protectant under UK conditions as part of an integrated strategy based on cooling and drying. Previous work has shown that a surface treatment of DE applied at 1-3 g/kg prevents development of surface arthropods for a storage season, if the bulk is cooled to 5 deg C by December. For these experiments, samples were scooped from the surface of treated and untreated bulks of wheat and used to set up efficacy tests under controlled laboratory conditions. Bioassays were carried out at temperatures of 10, 15 and 25 deg C and moisture contents of 16-17 percent using two mite and two insect species. Mean percentage population inhibition was calculated for surface doses of 3, 2 and 1 g/kg after one generation.All doses achieved 100 percent inhibition against the mites, Acarus siro and Lepidoglyphus destructor, with the exception of 1 g/kg at 25 and 15 deg C for A. siro and 2 g/kg at 25 deg C for L. destructor (99.9 percent). For the insects, 100 percent inhibition was achieved for Oryzaephilus surinamensis, but developing stages of Sitophilus granarius within the kernel escaped treatment, resulting in inhibitions of 61-99 percent, depending on dose and temperature. However, this reduction in population compared to the controls showed that the treatment clearly affected the number of eggs laid. Samples from the 2 g/kg treatment were also used to estimate the evenness of surface treatment. The dose achieved across the surface was between 0.55 and 3.46 g/kg.Although uneven, there was no indication that this affected efficacy between paired treatments. These results also suggest that DE treatments will still give protection during different stages of cooling and against surface populations that may occur during summer warming and prolonged storage.