Host plants affect the susceptibility of Spodoptera exigua to its homologous nucleopolyhedrovirus: role of chitin synthase and intestinal mucin in the peritrophic matrix

Abstract

ABSTRACT Host plants have an effect on the susceptibility of lepidopteran insects to nucleopolyhedrovirus (NPV), but the role of the protein in peritrophic membrane (PM) of larvae has not been investigated. We determined a key PM gene (SeIIM8 gene) in Spodoptera exigua (Hübner), which plays a role in protecting against NPV infection. Then we quantified the activity of chitin synthase (SeCHS), the content of insect intestinal mucin (SeIIM) and the expression of their genes in S. exigua fed one of four foods (artificial diet, Brassica oleracea (L.), Glycine max (L.), or Ipomoea aquatica (Forsskal)) with or without inoculation of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV). Our results showed that the larval mortality was highest for NPV-infected with siRNA-injected larvae, intermediate for NPV-infected larvae, and lowest for uninfected larvae. The SeCHS activity, SeIIM content, and their relative gene expressions of S. exigua fed G. max or artificial diet were lower compared to caterpillars fed other diets. The relative SeCHS and SeIIM8 gene expression levels of larvae depended on the interaction of NPV treatment, diet, and time. This study concluded that plants affected the susceptibility of insects to NPV by altering the enzyme activity and gene expression of insects.