Insecticidal and Residual Effects of Spinosad, Alpha-Cypermethrin, and Pirimiphos-Methyl on Surfaces Against Tribolium castaneum , Sitophilus granarius , and Lasioderma serricorne

Contact insecticides are classified into two categories: as grain protectants, which are applied directly on grains, and as surface treatments, which are applied on cracks and crevices. The aim of this study was to evaluate the long-term residual efficacy of these insecticides across different surfaces and target species. Thus, we investigated the efficacy of three insecticidal formulations, spinosad, alpha-cypermethrin, and pirimiphos-methyl against stored product beetles on different surfaces (concrete, metallic, plastic, and ceramic). Adults of Tribolium castaneum , Sitophilus granarius , and Lasioderma serricorne were used in the experiments. Bioassays were carried out during a six-month period, with mortality measured after 3, 7, 14, and 21 days after exposure. Among the different insecticides tested, spinosad was the least effective against T. castaneum , especially on concrete, where mortality had decreased to zero by Month 2, whereas in most of the cases, close to 100% was recorded. Regarding S. granarius , pirimiphos-methyl and spinosad remained effective on ceramic and metallic surfaces for a six-month period, whereas alpha-cypermethrin had the lowest mortality rate. For L. serricorne , spinosad caused high mortality levels, whereas pirimiphos-methyl was the least effective after Month 4. Based on our finding, among the tested insecticides, spinosad had the long-term residual effect on stored product protection.