Efficacy of spinetoram as a contact insecticide on different surfaces against stored-product beetle species

Abstract

Contact toxicity of spinetoram was evaluated in laboratory bioassays on concrete, ceramic tile, galvanized steel, and plywood. The efficacy of spinetoram was assessed at dose rates of 0.025 mg (AI)/cm2, 0.05 mg (AI)/cm2, and 0.1 mg (AI)/cm2 in two series of bioassays. The first series was conducted on concrete surfaces, with adults of Rhyzopertha dominica (F.), Sitophilus oryzae (L.), S. granarius (L.), Tribolium confusum Jacquelin du Val, Oryzaephilus surinamensis (L.), and Cryptolestes ferrugineus (Stephens). The second series was conducted at the same dose rates on all surfaces against adults of R. dominica, S. oryzae, and T. confusum. An equal number of dishes with and without food were used in both bioassay series. Mortality was assessed daily for 7 days for T. confusum and after this interval all live adults were removed and transferred to untreated surfaces with food and held under the same conditions. After the first week of daily evaluation, delayed mortality was evaluated 7 days later. For all the other species, mortality was measured after 5 days of exposure. The results of the first series of bioassays showed that T. confusum was the least susceptible to spinetoram-treated concrete surfaces. In contrast, all the other species were found susceptible, regardless of the dose and the presence of food. Regarding the comparison of different surfaces, our results illustrate that, with the exception of T. confusum, there were no significant differences among surfaces. The results of the present study indicate that spinetoram was effective against various species on several types of surfaces, and the presence of food did not influence its efficacy in most cases.