Evaluation of Spinosad Applied to Grain Commodities for the Control of Stored Product Insect Pests

Abstract

The insect pests of stored food commodities are not only the pests of bulk grains but also of many value-added food products in mills, processing plants and storage facilities where these products are stored. The residual efficacy of spinosad was assessed by exposing the Oryzeaphilus surinamensis, Tribolium castaneum and Trogoderma granarium to the treated commodities (wheat, maize, rice and oats) at concentrations of 0.25, 0.50 and 1 mg Kg-1 under laboratory conditions maintained at 28 ± 2oC, 65 ± 5% RH and continuous darkness. Seven bioassays were conducted by releasing the insects on treated commodities after different post treatment periods (0,1, 2, 3, 4, 5 and 6 months). The mortality of three insect species was recorded at tested concentrations in all the treated commodities after the exposure period of 3 and 7 days. Overall results of all bioassays show that residual efficacy of spinosad was reduced with the increase of post treatment period. At 1 mg Kg-1, at the exposure period of 7 days, the mortality was more than 97% at month 0 and it was > 47.7% at month 5 in all the tested insect species on all grain types. Spinosad was more effective in oats followed by wheat, maize and rice in all the tested species. Results show that spinosad possess great potential for residual control of O. surinamensis, T. castaneum and T. granarium, and can be used for replacement of conventional neurotoxic insecticides for managing the insect pests of stored commodities.