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Understanding interactions between viruses and their hosts is conducive to enabling better application of viruses as biocontrol agents. Certain viruses carried by parasitic wasps enhance the parasitic efficiency of wasp-larvae by protecting them against the immune system of their Lepidopteran host. However, the relationship between prey pests and viruses found in predatory natural enemies remains unclear. Herein, we report the interaction between Arma chinensis virus-1 (AcV-1), originally isolated from a predatory natural enemy, Arma chinensis (Hemiptera: Pentatomidae), and one of its prey species, Spodoptera frugiperda (Lepidoptera: Noctuidae). The results showed that the AcV-1 virus appeared harmful to the novel host S. frugiperda by inhibiting larval diet consumption and increasing pupal mortality. Meanwhile, sequencing data indicated that the virus altered the gene expression profiles of S. frugiperda. KEGG analysis showed that the proteasome and phagosome pathways related to protein degradation and immune response were significantly enriched. Although the expression levels of digestive enzyme genes did not change significantly, the total protease activity of AcV-1 virus-positive individuals was significantly decreased, suggesting that the virus inhibited diet consumption of S. frugiperda via the down-regulation of digestive enzyme activities. These results indicate that a virus initially isolated in a predatory natural enemy can decrease the fitness of its prey species. The virus was found to impact the host proteasome and phagosome pathways related to protein degradation and immunity, providing a potential mechanism to enhance controlling efficiency.

As potential molecular targets for developing novel pest management strategies, odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) have been considered to initiate odor recognition in insects. Herein, we investigated the OBPs and CSPs in a major global crop pest (Spodoptera exempta). Using transcriptome analysis, we identified 40 OBPs and 33 CSPs in S. exempta, among which 35 OBPs and 29 CSPs had intact open reading frames. Sequence alignment indicated that 30 OBPs and 23 CSPs completely contained the conserved cysteines. OBPs of lepidopteran insects usually belonged to classical, minus-C, and plus-C groups. However, phylogenetic analyses indicated that we only identified 28 classical and seven minus-C OBPs in S. exempta, suggesting that we might have missed some typical OBPs in lepidopteran insects, probably due to their low expression levels. All of the CSPs from S. exempta clustered with the orthologs of other moths. The identification and expression of the OBPs and CSPs were well studied in insect adults by transcriptional analyses, and herein we used samples at different stages to determine the expression of OBPs and CSPs in S. exempta. Interestingly, our data indicated that several OBPs and CSPs were especially or more highly expressed in larvae or pupae than other stages, including three exclusively (SexeOBP13, SexeOBP16 and SexeCSP23) and six more highly (SexeOBP15, SexeOBP37, SexeCSP4, SexeCSP8, SexeCSP19, and SexeCSP33) expressed in larvae, two exclusively (SexeCSP6 and SexeCSP20) and three more highly (SexeOBP18, SexeCSP17, and SexeCSP26) expressed in pupae. Usually, OBPs and CSPs had both male- and female-biased expression patterns in adult antennae. However, our whole-body data indicated that all highly expressed OBPs and CSPs in adults were male-biased or did not differ, suggesting diverse OBP and CSP functions in insect adults. Besides identifying OBPs and CSPs as well as their expression patterns, these results provide a molecular basis to facilitate functional studies of OBPs and CSPs for exploring novel management strategies to control S. exempta.