Sequential and Simultaneous Interactions of Plant Allelochemical Flavone, Bt Toxin Vip3A, and Insecticide Emamectin Benzoate in Spodoptera frugiperda .

Target pests of genetically engineered crops producing both defensive allelochemicals and Bacillus thuringiensis (Bt) toxins often sequentially or simultaneously uptake allelochemicals, Bt toxins, and/or insecticides. How the three types of toxins interact to kill pests remains underexplored. Here we investigated the interactions of Bt toxin Vip3A, plant allelochemical flavone, and insecticide emamectin benzoate in Spodoptera frugiperda . Simultaneous administration of flavone LC 25 + Vip3A LC 25 , emamectin benzoate LC 25 + Vip3A LC 25 , and flavone LC 15 + emamectin benzoate LC 15 + Vip3A LC 15 but not flavone LC 25 + emamectin LC 25 yielded a mortality significantly higher than their expected additive mortality (EAM). One-day pre-exposure to one toxin at LC 5 followed by six-day exposure to the same toxin at LC 5 plus another toxin at LC 50 showed that the mortality of flavone LC 5 + Vip3A LC 50 , emamectin benzoate LC 5 + Vip3A LC 50 , and Vip3A LC 5 + emamectin benzoate LC 50 were significantly higher than their EAM, while that of flavone LC 5 + emamectin benzoate LC 50 was significantly lower than their EAM. No significant difference existed among the mortalities of Vip3A LC 5 + flavone LC 50 , emamectin benzoate LC 5 + flavone LC 50 , and their EAMs. The results suggest that the interactions of the three toxins are largely synergistic (inductive) or additive, depending on their combinations and doses.