Lesser grain borers, Rhyzopertha dominica, were exposed to wheat treated with 400ppm of the commercial diatomaceous earth Protect-ItTM at three different surface layer depths: 15.2, 22.9, and 30.5 cm (6, 9, 12 inches). Towers of wheat were constructed of twelve 7.6 cm x 7.6 cm (3 x 3 inch) sections of PVC pipe, for a total of 91.5 cm (3 feet). Each individual section was removable. One hundred adults were introduced into the top of the grain mass, the insects were exposed for 7, 10, and 14 days at 27oC and 32oC. There were 5 replicates; each replicate was done separately in a randomized complete block design. Upon completion of the exposure interval towers were taken apart, adults were removed, and mortality and distribution of adults was assessed. The wheat in each individual section was held for an additional 8 weeks at the same exposure conditions, at which point the F1 production was assessed and percentage of insect damaged kernels was recorded. The wheat and insects were then discarded. Results suggest that mortality decreases with temperature, and increases with depth of the treated layer and the exposure interval. Insects were more mobile at 32oC than at 27oC, and penetrated deeper into the wheat column. Progeny production increased with the higher temperature, and the percentage of insect-damaged kernels was proportional to the number of progeny in each section of the towers.
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