ECOLOGY, GENOMICS, AND MANAGEMENT OF STORED PRODUCT INSECTS
Location: Stored Product Insect Research Unit
Title: Lethal and sub-lethal effects from short-term exposure of Rhyzopertha dominica on wheat treated with Storicide II®
Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 27, 2011
Publication Date: April 1, 2012
Citation: Arthur, F.H. 2012. Lethal and sub-lethal effects from short-term exposure of Rhyzopertha dominica on wheat treated with Storicide II®. Journal of Pest Science. 85(2): 261-265. http://dx.doi.org/10.1007/s10340-011-0396-8.
Interpretive Summary: When pest insects are exposed on treated stored grains, mortality may not immediately occur. A study was conducted by exposing adult male and female lesser grain borers on stored wheat treated with different concentrations of the insecticide Storicide II®, for different time periods, and then transferring them to untreated wheat. At the lower concentrations or shorter exposure times, the parent beetles survived exposure, females were less susceptible than males, and they were able to produce offspring on the untreated wheat. As the concentration and/or exposure time increased, the exposed parent beetles died and the production of offspring declined, indicating that death occurred before mating or egg-laying. Results show males may be more susceptible to Storicide II® than females, and there may be a delayed mortality effect on the exposed parental adults that will affect production of offspring.
Hard red winter wheat was treated at 0 (untreated control), 25, 50, 75, and 100% of the label rate of the insecticide Storicide II®, which is chlorpyrifos-methyl and deltamethrin applied at label rates of 3 and 0.5 ppm, respectively. Paired male and female Rhyzopertha dominica F., the lesser grain borer, were exposed on wheat treated at each of the 5 rates at 27°C-60% r.h. for one week for 2, 4, 8, 16, and 32 hours, and transferred to untreated wheat held at the same environmental conditions. Parental adults were removed after one week, mortality was assessed, and the wheat was held for 7 weeks at the same environmental conditions to determine progeny production. As the concentration and exposure interval increased, mortality of both sexes approached 100%, but at the intermediate concentration-time combinations male mortality was greater than female mortality. Progeny production also decreased with increasing concentration of Storicide II® as the exposure time increased, with non-linear patterns of decrease at the lower concentrations and time combinations and linear decline at the higher levels of concentration and time. Results seem to indicate greater susceptibility of males to Storicide II®, and also show delayed parental mortality from the insecticide exposure and sub-lethal effects of reduced progeny production.