No abstract

No abstract

BACKGROUND Tri‐trophic interactions among plants, insect herbivores and entomopathogens are one of the hot topics in ecology. Although plants have been shown to impact the interactions between herbivores and entomopathogens, it is still unclear how plants affect the cellular immunity of herbivores to entomopathogens. RESULTS The number of hemocytes and the proportion of two main cell types (granular hemocytes and plasmatocytes), plasmatocyte‐spreading rate, apoptosis rate, two Spodoptera exigua caspase (SeCasp‐1, SeCasp‐5) activities and gene expressions were all higher and the activities and gene expression of S. exigua inhibitor of apoptosis protein (SeIAP) were lower in nucleopolyhedrovirus (NPV)‐infected caterpillars fed Ipomoea aquatica than those fed other plants or artificial diet. Scanning electron microscopy images were consistent with molecular patterns of immune responses. CONCLUSION This study suggests that host plants affect the immune responses of herbivores to entomopathogens by manipulating the composition, morphology and apoptosis of herbivore hemocytes, which sheds light on the mechanisms that allow host plants to influence multi‐trophic interactions. © 2021 Society of Chemical Industry

It has been reported that host plants are able to mediate the interactions between insect herbivores and entomoviruses, but how plants affect growth, development, detoxifying enzymes and metabolic enzymes of herbivores infected by entomoviruses has only rarely been studied so far. We compared growth, development duration, activity of a detoxifying enzyme (carboxylesterase) and a metabolic enzyme (acetylcholinesterase) of a caterpillar (Spodoptera exigua) infected with an entomovirus (SeMNPV) or left non‐infected that were fed one of four plants (Ipomoea aquatica, Brassica oleracea, Glycine max or Zea mays). Developmental duration was shorter but growth (length, mass) and enzyme activities were higher in NPV‐infected caterpillars fed I. aquatica or B. oleracea than those fed G. max or Z. mays. This study suggests that host plants influence the growth impacts of entomoviruses on herbivores by affecting the enzymes of herbivores.

Plant-mediated effects on the susceptibility of insect herbivores to entomoviruses are well recognized, but the mechanisms by which plant secondary metabolites impact susceptibility are poorly understood. With widely targeted metabolomics analyses of three plants (Glycine max, Brassica oleracea, Ipomoea aquatica) that caused significant differences in caterpillar (Spodoptera exigua) viral susceptibility, we found four plant phenolics (genistein, kaempferol, quercitrin, coumarin) that increased susceptibility. Subsequently, we analyzed transcriptomes of caterpillars treated with nucleopolyhedrovirus (NPV) alone or with one the four plant phenolics to examine differences in metabolic pathways. We found that phenolic treatments caused significant differences in genes up-or-down regulating cytochrome P450, glutathione S-transferase and consistently caused significant down-regulation of the CXE18 gene regulating antennal esterase in caterpillars. This study found four phytochemicals can be potential candidate NPV synergist and sheds light on the mechanisms driving insect susceptibility to entomoviruses.