Submitted to: Crop Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/21/2006
Publication Date: 4/30/2007
Citation: Chanbang, Y., Arthur, F.H., Wilde, G.E., Throne, J.E. 2007. Efficacy of diatomaceous earth to control Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in rough rice: Impacts of temperature and relative humidity. Crop Protection. 26(7): 923-929. Doi: http://dx.doi.org/10.1016/j.cropro.2006.08.009. Interpretive Summary: Different commercial formulations of inert dusts diatomaceous earth (DE) are labeled to control insect pests of stored grain; however, the specific grain type may sometimes affect the level of control from insecticide applications. We treated rough rice with the labeled application rates of two commercial DE products and exposed adult lesser grain borers for different time periods for up to one week, at temperatures of 80 and 90°F. Adult mortality increased with increasing time of exposure up to a maximum of 60 to 70% for both commercial formulations, and there was extensive progeny production in the treated rice, especially at 90°F. Results show that although these two commercial DE formulations had previously given good control of the lesser grain borer on stored wheat, they were not as effective on rough rice. It may be necessary to combine DE with another insecticide to give complete control of the lesser grain borer on rough rice.
Technical Abstract: Laboratory trials were conducted to determine the effectiveness of diatomaceous earth (DE) against Rhyzopertha dominica (F.), the lesser grain borer, on stored rough rice. Two DE commercial products, Insecto and Protect-It, were applied at their respective label rates of 500 and 400 ppm to long grain rice by hand-mixing the DE with the rice. R. dominica were exposed for varying time intervals, mortality was assessed, and rice was held at different temperatures and relative humidities (r.h.) for 8 weeks until F1 adult emergence. There was a significant difference in mortality between the DE treatments and untreated controls (P < 0.01), but no significant differences with respect to the two DE products (P > 0.05). Mortality increased as exposure interval increased, and ranged from 15.8 to 69.2%, depending on the exposure interval. Although the general ANOVA showed a significant difference for temperature and r.h., when mortality and r.h. were compared only 5 out of 30 comparisons were significant (P < 0.05). There was extensive progeny production in all treatments (including controls) and more progeny were produced at 32 than at 27°C. The overall ANOVA showed a difference for treatment and RH, but again few comparisons were significant (P < 0.05). Results showed that the two DE products did not completely suppress R. dominica on rough rice, and combination treatments with another insecticide may be necessary to give complete control.