Submitted to: Journal of Stored Products Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/25/2006
Publication Date: 10/1/2007
Citation: Vardeman, E.A., Arthur, F.H., Nechols, J.R., Campbell, J.F. 2007. Efficacy of surface applications with diatomaceous earth to control Rhyzopertha dominica (F.) (Coleoptera: Boxtrichidae) in stored wheat. Journal of Stored Products Research. 43(4): 335-341. Doi: http://dx.doi.org/10.1016/j.jspr.2006.08.003. Interpretive Summary: Diatomaceous earth (DE) is a reduced-risk insecticide that is composed primarily of the remains of fossilized diatoms. There are several commercial formulations of DE that can be used to treat stored wheat, but there is little information available regarding efficacy of these different products and whether mixing DE into the top lawer of grain, rather than treating the whole grain bulk, would provide adequate insect control. We mixed commercial formulations of DE at their respective label rates for surface treatment of wheat into a 12-inch layer of treated wheat on top of untreated wheat in a vertical column, and released live adult lesser grain borers on the surface. Adults were able to penetrate the treated grain mass and reproduce in the untreated wheat, but survival and reproduction were lower in wheat treated with the label rate of 1,000 ppm Dryacide®, compared to the lower rates of 500 ppm Insecto™ and 400 ppm Protect-It®. Insect control is apparently dose-dependent and related to a specific DE formulation, but as the amount of DE is increased, physical properties of grain could be adversely affected. This information will be useful to storage managers in selecting DE formulations for insect control and for determining method of application.
Technical Abstract: Commercial formulations of diatomaceous earth (DE) products are labeled for use as surface treatments in stored wheat. However, they have not been evaluated as such against the lesser grain borer, Rhyzopertha dominica (F.), a major pest of stored wheat. An experiment was conducted at two temperatures (27 and 32°C) and three exposure intervals (7, 10, 14 d) to determine if R. dominica could penetrate a layer of wheat treated with the labeled rates of three commercial formulations of DE, and, if so, to measure rates of adult survival and progeny production. When R. dominica adults were introduced to wheat admixed with DE to a depth of 30.5 cm, they were able to penetrate the DE-treated layer and oviposit in the untreated wheat below. Both adult survival and progeny production were significantly lower in wheat mixed with Dryacide® (1,000 ppm) as compared to Insecto™ (500 ppm), Protect-It® (400 ppm) or the untreated control. Temperature and exposure interval had no effect on adult survival or progeny production. The vertical displacement patterns of adults were significantly different among DE treatments, but not for temperature or exposure intervals. More R. dominica traveled a greater distance in the untreated control, followed by InsectoTM, Protect-It®, and then Dryacide®. Results indicate that R. dominica can penetrate a surface layer of DE-treated wheat and reproduce within and below it, but this penetration and subsequent population growth vary depending on the DE product used. It is also possible that pest suppression is dose-dependent, or it may depend on a combination of application rate and specific DE formulation. Results of this study indicate that Dryacide® at 1,000 ppm could be used as a surface treatment or in combination with other control strategies to suppress R. dominica populations in stored wheat.