Allicin impacts the susceptibility of Spodoptera exigua to nucleopolyhedrovirus

Plant secondary metabolites are crucial in affecting the interactions between insect herbivores and entomoviruses. However, there is limited knowledge regarding the impact of such metabolites on the susceptibility of insect herbivores to entomoviruses. In this study, we adopted the allicin, caterpillars (Spodoptera exigua) and nucleopolyhedrovirus (SeMNPV) as a system, and found that allicin significantly increased the mortality of S. exigua larvae infected with SeMNPV by 36.03–59.45% when infected with the virus at a concentration of 2.12 × 103 OB·mL−1. Furthermore, NPV-infected larvae together treated with allicin inhibited the growth and development of larvae, comparing to individual NPV-infected larvae. Notably, we observed a significant enrichment of differentially expressed genes involved in the cytochrome P450-mediated metabolism pathway between the NPV-infected and allicin combined with NPV-treated groups. The silencing of CYP340AA1 through RNA interference significantly increased the mortality of larvae infected with SeMNPV. This investigation indicates that allicin might be a potential candidate for improving the performance of the NPV against insect herbivores and identifies that CYP340AA1 gene is important in this process.