Combinations of spintor with botanical powders as toxicants against red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Postharvest insect pests constitute major threats to food security because they cause qualitative and quantitative damage to agricultural produce. Therefore, eco-friendly and cost-effective measures should be used for their management. In this study, five botanical powders ( Trema orientalis and Crataeva religiosa leaves; and Citrus tangelo, Citrus maxima and Citrus aurantifolia peels) were admixed with Spintor® [1.25 active ingredient (a.i.) mg · kg –1] and evaluated as toxicants against Tribolium castaneum. Each botanical powder and spintor was solely applied at 1000 mg · kg –1 millet seeds. Spintor-botanical powder mixtures admixed at a ratio of 1 : 1 (w/w) were applied at 500 and 1000 mg · kg –1, corresponding to 0.313 and 0.625 a. i. mg · kg –1 for spintor in the mixtures, respectively. On the 14th day of exposure, the Citrus species admixed with spintor and applied at 500 mg · kg –1 evoked significantly (p < 0.05) higher percentage mortality (72.22–90.28%) than what was observed in the mixture of spintor with T. orientalis (22.08%) or the mixture of spintor with C. religosa (17.92%) applied at 500 mg · kg –1. There was a significant difference (p < 0.05) in the Kaplan-Meier estimates of the treatments against the insects. The time required to kill 50% of the assayed insects (LT50) when Citrus species were admixed with spintor at 500 mg · kg –1 (10 days) was shorter than 14 days observed in the mixture of spintor with T. orientalis or C. religiosa. Therefore, admixing spintor with any of the Citrus powders [at 1 : 1 (w/w)] applied at 500 mg · kg –1 seed is recommended for the protection of millet seeds against T. castaneum.