Sequential and simultaneous interactions of plant allelochemical flavone, Bt toxin Vip3A and insecticide emamectin benzoate in Spodoptera frugiperda

Authors: HUANG, KAIYUAN - Zhengzhou University; HE, HAIBO - Zhengzhou University; WANG, SHAN - Zhengzhou University; ZHANG, MIN - Zhengzhou University; CHEN, XUEWEI - Zhengzhou University; DENG, ZHONGYUAN - Zhengzhou University; Ni, Xinzhi; LI, XIANCHUN - University Of Arizona

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2023
Publication Date: 8/31/2023
Citation: Huang, K., He, H., Wang, S., Zhang, M., Chen, X., Deng, Z., Ni, X., Li, X. 2023. Sequential and simultaneous interactions of plant allelochemical flavone, Bt toxin Vip3A and insecticide emamectin benzoate in Spodoptera frugiperda. Insects. 14(9):736. https://doi.org/10.3390/insects14090736.
DOI: https://doi.org/10.3390/insects14090736

Interpretive Summary: The widespread cultivation of genetically engineered crops producing not only toxic proteins from a bacterium (Bt), but also plant defensive compounds, in combined with occasional use of insecticides, are the major tactics to manage key 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 pest damage. The current study examined the sequential and simultaneous interactions of plant defensive compound (flavone), Bt toxin (Vip3A) and insecticide (emamectin benzoate) in the management of fall armyworm, one of the worldwide target pests of Bt crops. Bioassays of newly hatched fall armyworm larvae revealed that interactions of all three toxins, except for 1-day pre-exposure to a sublethal dose of flavone followed by 6-day simultaneous exposure to sublethal dose of flavone plus lethal dose of insecticide, could either synergistically (inductive) or additively increase larval mortality. The results demonstrated that the combined use of the three types of toxins (i.e., transgenic Bt toxin, plant defensive compound, and insecticide) has the potential to be an effective and sustainable strategy to manage fall armyworm damage on crop plants.

Technical Abstract: 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 LC25 + Vip3A LC25, emamectin benzoate LC25 + Vip3A LC25, and flavone LC15 + emamectin benzoate LC15 + Vip3A LC15 but not flavone LC25 + emamectin LC25 yielded a mortality significantly higher than their expected additive mortality (EAM). One-day pre-exposure to one toxin at LC5 followed by 6-day exposure to the same toxin at LC5 plus another toxin at LC50 showed that the mortality of flavone LC5 + Vip3A LC50, emamectin benzoate LC5 + Vip3A LC50, and Vip3A LC5 + emamectin benzoate LC50, were significantly higher than their EAM, while that of flavone LC5 + emamectin benzoate LC50 was 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.