Residual Efficacy of Pyriproxyfen on Grain Commodities Against Stored Product Insect Pests

Abstract

Studies on residual efficacy of insecticides with reduced risk are necessary for strategies on their use and application frequency. Within these insecticides, insect growth regulators, such as pyriproxyfen, have been successfully used to control stored grain pests. The objective of this study was to evaluate the residual efficacy of pyriproxyfen in larvae of the stored grain pests Oryzaephilus surinamensis, Tribolium castaneum and Trogoderma granarium. Grains of wheat, maize, rice, and oats were exposed to pyriproxyfen at concentrations of 1, 2 or 4 mg kg−1. Six bioassays were performed by releasing the insects on treated grains after different post treatment periods (0, 2, 4, 8, 12 and 16 weeks). Adult emergence of the three insect species was reduced at tested concentrations in all treated grains. For all bioassays the residual efficacy of pyriproxyfen decreased with increase in the post treatment period. At 4 mg kg−1, the adult emergence did not exceed 16% at week 0 and it was <40% at week 12 in all tested insect species on all grains, but it increased at week 16. The residual effect of pyriproxyfen was more effective in wheat followed by oats, maize and rice for T. castaneum and T. granarium, whereas against O. surinamensis pyriproxyfen was more effective in oats followed by wheat, maize and rice. Results show that pyriproxyfen has potential for residual control of O. surinamensis, T. castaneum and T. granarium, and may be used for replacement of conventional neurotoxic insecticides for managing the insect pests of stored commodities.