Effect of partial and complete treatments of wheat kernels with spinosadon Rhyzopertha dominica (F.) adult mortality and egg-to-adult emergence

Abstract: Spinosad was registered in 2005 as a grain protectant in the United States at themaximum label rate of 1ppm or mg (AI) kg-1 of grain. In a laboratory study conducted at 28°Cand 65% RH, the effects of treating the germ end, endosperm end and whole kernel of wheat withliquid formulation of spinosad at 0.1 and 1mg (AI) ml-1 on responses of the lesser grain borer,Rhyzopertha dominica (F.), were studied. The purpose was to show if treating a portion of akernel was as good as treating the entire kernel in terms of insect mortality and progenyproduction. The low spinosad concentration of 0.1mg (AI) ml-1 resulted in spinosad deposition onkernels that ranged from 0.72 to 1.20ppm, and the concentration of 1.0mg (AI) ml-1 resulted inresidues that were 5 to 10 times higher. Dipping portions of wheat kernels or the entire kernel atthe low rate resulted in 100% mortality of R. dominica adults within 7 to 14 days, and resulted incomplete to near complete suppression of adult progeny production and kernel damage. The eggto-adult emergence of R. dominica was also effectively suppressed irrespective of the kernelportions treatment. At the low spinosad concentration, ≥ 50% of the kernels needed to becompleted treated with spinosad to produce 100% of R. dominica adults.