Genetically engineered crops simultaneously produce defensive allelochemicals and Bacillus thuringiensis (Bt) toxin proteins to kill some of the world's most devastating insect pests. How the two types of toxins, when ingested sequentially or simultaneously, interact at both lethal and sublethal doses in these pests remains underexplored. Here, we examined the toxicological interactions between the Bt toxin Cry1Ac and the flavonoid allelochemical flavone in Helicoverpa armigera . Simultaneous exposure of H. armigera neonates to lethal doses (LC 25 ) of Cry1Ac and flavone caused a mortality significantly higher than that of either toxin alone and their expected additive mortality. Preexposure for 24 h to a sublethal dose (LC 10 ) of Cry1Ac followed by 6-d simultaneous exposure to the same dose of Cry1Ac plus a lethal dose (1.6 mg/g diets, LC 50 ) of flavone resulted in a mortality significantly higher than that of the LC 50 dose of flavone alone and the expected additive mortality of the LC 50 dose of flavone plus the LC 10 dose of Cry1Ac. One-day preexposure to the sublethal dose (LC 10 ) of flavone followed by 6-d simultaneous exposure to the LC 50 dose (6 ng/cm 2 ) of Cry1Ac plus the LC 10 dose of flavone yielded a mortality significantly higher than that of the LC 50 dose of Cry1Ac but similar to the expected additive mortality of the LC 50 dose of Cry1Ac plus the LC 10 dose of flavone. The results suggest that Cry1Ac induces and synergizes the toxicity of flavone against H. armigera larvae.
Kaiyuan Huang,Haibo He,Shan Wang,Min Zhang,Xuewei Chen,Zhongyuan Deng,Xinzhi Ni,Xianchun Li
Simple SummaryThe widespread cultivation of genetically engineered crops producing not only toxic proteins from the bacteriumBacillus thringiensis(Bt) but also plant defensive compounds known as allelochemicals, combined with occasional use of insecticides, is the major tactic to manage some economically important pests. Better understanding of the toxicological interactions of the three types of toxins is needed to rationally deploy them to protect crops from pests. The aim of this study is to examine the sequential and simultaneous interactions of the allelochemical flavone, Bt toxin Vip3A, and insecticide emamectin benzoate in the fall armyworm (Spodoptera frugiperda), a worldwide target pest of Bt crops. Bioassays ofS. frugiperdaneonates revealed that all interactions of the three toxins, except for 1-day pre-exposure to a sublethal dose (LC5) of flavone followed by 6-day simultaneous exposure to flavone LC5+ emamectin benzoate LC50, are synergistic or additive. The results suggest that the combined use of the three toxins is basically a great strategy to manageS. frugiperda.AbstractTarget pests of genetically engineered crops producing both defensive allelochemicals andBacillus 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 inSpodoptera frugiperda. Simultaneous administration of flavone LC25+ Vip3A LC25, emamectin benzoate LC25+ Vip3A LC25, and flavone LC15+ emamectin benzoate LC15+ Vip3A LC15but not flavone LC25+ emamectin LC25yielded a mortality significantly higher than their expected additive mortality (EAM). One-day pre-exposure to one toxin at LC5followed by six-day exposure to the same toxin at LC5plus another toxin at LC50showed that the mortality of flavone LC5+ Vip3A LC50, emamectin benzoate LC5+ Vip3A LC50, and Vip3A LC5+ emamectin benzoate LC50were significantly higher than their EAM, while that of flavone LC5+ emamectin benzoate LC50was significantly lower than their EAM. No significant difference existed among the mortalities of Vip3A LC5+ flavone LC50, emamectin benzoate LC5+ flavone LC50, 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.Keywords:allelochemical;Bt toxin;chemical insecticide;combined toxicity;induced toxicity;synergistic interactions
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