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Title: Insecticidal effect of spinosad dust, in combination with diatomaceous earth, against two stored-grain beetle species

item Arthur, Franklin

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2008
Publication Date: 12/1/2008
Citation: Chintzoglou, G., Athanassiou, C.G., Arthur, F.H. 2008. Insecticidal effect of spinosad dust, in combination with diatomaceous earth, against two stored-grain beetle species. Journal of Stored Products Research. 46(4): 347-353. doi:

Interpretive Summary: Spinosad is a biological pesticide that has been evaluated for control of stored-grain beetles, but the dust formulation has not been extensively tested. We conducted tests by evaluating Spinosad dust applied alone and in combination with the natural inert dust diatomaceous earth (DE) on wheat and corn, with the rice weevil and the confused flour beetle as the target pests. Spinosad alone was more effective on wheat and corn for control of the rice weevil, and adding the DE increased rice weevil mortality on corn. The confused flour beetle was more difficult to kill on both commodities compared to the rice weevil, but adding the DE gave increased mortality of this species as well. Applying spinosad in combination with DE may be necessary to give effective control of beetle pests of stored wheat and other stored products.

Technical Abstract: Efficacy of the biological insecticide spinosad applied alone and combination with diatomaceous earth (DE) was determined through laboratory bioassays with adults of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). Wheat and maize were treated with 50, 150, and 500 ppm of spinosad dust formulation (corresponding to 0.0625, 0.1875, and 0.625 ppm of active ingredient [AI]) for S. oryzae and 150, 500, and 1,000 ppm of spinosad dust (corresponding to 0.1875, 0.625, and 1.25 ppm of AI) for T. confusum, alone and in combination with the DE SilicoSec at 150 ppm for S. oryzae and 250 ppm for T. confusum. Mortality of S. oryzae exposed for 14 d on wheat treated with spinosad ranged between 82 and 100%, and was 99% when exposed on wheat treated with DE. Conversely, mortality of S. oryzae on maize did not exceed 19% when exposed on DE or on maize treated with 50 or 150 ppm spinosad dust, and was 59% on the 500-ppm spinosad dust treatment. However, the presence of the DE generally led to an increase in mortality of S. oryzae on maize. For T. confusum, mortality on both commodities was lower than that for S. oryzae. After 14 d of exposure on wheat, mortality was only 14% at 1,000 ppm of spinosad, but increased to 33% in the presence of DE. Similar results were also obtained for T. confusum exposed on treated maize, which indicated a possible synergistic effect between spinosad and DE. Although no synergistic effect was noted in parental mortality of S. oryzae, the inclusion of DE reduced progeny production in comparison with spinosad alone. Progeny production of T. confusum was relatively low in all treatments, compared to progeny production of S. oryzae. Results show the potential of combination treatments of spinosad dust and DE, but efficacy may vary depending on the target insect species.