Contact toxicity of insecticides against adults and larvae of Cadra cautella (Walk.) and Oryzaephilus surinamensis (L.)

Effective insecticide options for managing stored-product pests are increasingly limited, necessitating the exploration of alternatives to conventional insecticides such as malathion and deltamethrin. The saw-toothed grain beetle, Oryzaephilus surinamensis and almond moth, Cadra cautella are major storage pests that cause substantial quantitative and qualitative losses to stored grains and processed products. However, limited studies have evaluated the contact toxicity of alternative insecticides against different life stages of these pests. This study aimed to assess the efficacy of four insecticides viz., lambda-cyhalothrin, spinosad, spinetoram, and chlorfenapyr against both adult and larval stages of O. surinamensis and C. cautella through laboratory bioassays at 24, 48, and 72 h of exposure. Among the tested insecticides, spinetoram exhibited the highest toxicity against C. cautella adults, with relative toxicity values of 2.43 and 3.13 compared to deltamethrin and malathion, respectively. Lambda-cyhalothrin was the most toxic to O. surinamensis adults, with relative toxicity values of 55.23 and 9.23. Larvae showed greater susceptibility than adults, with spinetoram displaying the highest toxicity against C. cautella larvae (42.82 and 9.56 relative toxicity), while lambda-cyhalothrin was most toxic to O. surinamensis larvae (21.23 and 10.04 relative toxicity). These findings highlight the potential of spinetoram and lambda-cyhalothrin as effective alternatives to conventional insecticides for pest management in bulk grain storage.