Sf-FGFR and Sf-SR-C Are Not the Receptors for Vip3Aa to Exert Insecticidal Toxicity in Spodoptera frugiperda

Vip3Aa is a novel insecticidal protein secreted by Bacillus thuringiensis (Bt) during its vegetative growth stages. It has high insecticidal activity against lepidopteran pests such as Spodoptera frugiperda, and has no cross-resistance with Cry insecticidal proteins. As a new type of insecticide, it plays an important role in controlling agricultural pests. However, the insecticidal mechanism of the Vip3Aa toxin, especially its definite receptors, have not been fully revealed. In this study, the previously reported Vip3Aa receptor genes Sf-FGFR and Sf-SR-C were knocked out separately using the CRISPR/Cas9 system. Bioassay results showed that the sensitivity of these two knockout strains to Vip3Aa were not significantly changed compared to that of the normal strain. The current results are not consistent with the previously reports that Sf-SR-C and Sf-FGFR were the receptors of Vip3Aa in vitro. This suggests that the Sf-SR-C and Sf-FGFR genes we tested may not be critical in the mode of action of Vip3Aa in vivo in Spodoptera frugiperda.