Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/4/2006
Publication Date: 7/1/2006
Citation: Vardeman, E.A., Arthur, F.H., Nechols, J.R., Campbell, J.F. 2006. Effect of temperature, exposure internal and depth of diatomaceous earth on distribution, mortality, and reproduction of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in stored wheat. Journal of Economic Entomology 99: 1017-1024. Interpretive Summary: Stored wheat is often treated for insect control with the inert dust diatomaceous earth (DE) by mixing the dust into the top surface of the wheat mass. However, we don't know if this method of application would effectively control the lesser grain borer, a major pest of stored wheat. We put 6, 9, and 12-inch layers of treated wheat on top of untreated wheat in a vertical column, and released live adult lesser grain borers on the surface. Adult mortality increased with increasing depths of the DE-treated layer, as expected, but we still found live lesser grain borer progeny in the untreated wheat. Adults apparently were able to penetrate through the DE-treated layer and lay eggs before they died. Results indicate that surface-layer treatments may not give complete control of the lesser grain borer.
Technical Abstract: Diatomaceous earth (DE) can be used as a surface treatment in stored wheat, but it is not known how the thickness of a treated layer, i.e. wheat and DE combined, impacts effectiveness. Therefore, a growth chamber experiment was conducted to assess the effect of DE on spatial distribution, adult survival and progeny production of the lesser grain borer, Rhyzopertha dominica (F.), on hard winter wheat grain, and to determine if temperature, depth of DE treatment, and exposure interval modified this effect. When adult lesser grain borers were introduced to experimental towers containing untreated wheat or wheat admixed with DE to a depth of 15.2, 22.9 or 30.5 cm, they were able to penetrate all DE layers and oviposit in the untreated wheat below. However, survival was significantly reduced in adults exposed to DE. Survival decreased with increasing size of the DE-depth and exposure interval. Temperature had no effect on adult survival, but significantly more progeny were produced at 32 than at 27°C. Progeny production was inversely correlated with the depth of the DE-treated layer. Distribution patterns of parental beetles were not significantly different among the treatments or exposure intervals; however more insects penetrated further at 32 than at 27°C. The F1 production was reduced by 22% at the thickest DE-treated layer. However, survival at this level could leave a residual population of lesser grain borers that would probably be above an allowable threshold for insect damage.