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.