Treatment of Four Stored-Grain Pests with Thiamethoxam plus Chlorantraniliprole: Enhanced Impact on Different Types of Grain Commodities and Surfaces

SIMPLE SUMMARY: Among pests threatening stored food, Rhyzopertha dominica, Tribolium castaneum, Trogoderma granarium, and Sitophilus oryzae are highly dangerous because they cause considerable losses around the world. Taking into account that there is a narrow available spectrum of contact insecticides for the management of stored-grain insects, a laboratory study was conducted to evaluate an insecticidal formulation containing two active ingredients, i.e., thiamethoxam plus chlorantraniliprole, when applied on grains and different surfaces against adults of the aforementioned species. Complete mortality was observed for S. oryzae on all three commodities, for R. dominica on wheat and rice, and for T. castaneum on wheat, 14 days post-initial exposure at the highest dose. At the end of the 90-day storage period, S. oryzae showed the maximum mortality, whereas T. granarium showed the lowest. Bioassays on surfaces revealed that thiamethoxam plus chlorantraniliprole applied on metal killed more adult individuals of all species than on cement, ceramic, or wood. Sitophilus oryzae was found to be the most sensitive on metal, followed by R. dominica, T. castaneum, and T. granarium. ABSTRACT: An insecticide containing the neonicotinoid thiamethoxam + the diamide chlorantraniliprole was evaluated against adults of Rhyzopertha dominica, Tribolium castaneum, Trogoderma granarium, and Sitophilus oryzae under laboratory bioassays both on freshly treated grain as well as on treated grain stored over 90 days for its persistence in efficacy. In laboratory bioassays, the insecticide was applied on wheat, maize, or rice at four doses, while in persistence bioassays on wheat at the same doses. Mortality and progeny were assessed in both laboratory and persistence bioassays. After 14 days of exposure, S. oryzae exhibited 100% mortality on all three commodities at the highest dose, while R. dominica showed complete mortality on wheat or rice and T. castaneum on wheat. For a period of 90 days, S. oryzae exhibited 42.69% mortality, followed by R. dominica (35.26%), T. castaneum (27.08%), and T. granarium (18.63%) at the highest dose. Progeny was successfully suppressed in all cases of complete mortality in laboratory bioassays and for S. oryzae for 90 days in persistence bioassays. Laboratory trials were also performed on plywood, concrete, ceramic tile, and steel at one dose. The highest mortality was observed on steel, followed by concrete, ceramic tile, and plywood for all insect species tested. This study demonstrates that thiamethoxam + chlorantraniliprole is effective against the tested species depending on exposure, storage period, surface, commodity, and dose.