Phospholipase A2 (PLA2) hydrolyzes fatty acids from phospholipids at sn-2 position. Two immune-associated PLA2s are known in Spodoptera exigua. Both are calcium-independent cellular PLA2 (iPLA2A and iPLA2B). These iPLA2s are inducible to immune challenge using different epitopes such as virus, Gram+, Gram- bacteria, and fungi. However, their expression profiles are different between these two iPLA2s. Especially, immune challenge with Gram+ bacteria and fungi significantly up-regulated these iPLA2 expression, suggesting their expression under Toll signal pathway. RNA interferences of Toll or IMD signal components are being investigated.

Based on Drosophila model, Toll and Imd signals have regared as central intracellular pathways in insect immune cells in response to various pathogens. Current insect genome studies have identified the corresponding orthologs in other insets. This study reports two immune signaling genes, Se-Toll-1 and Se-Relish-1, and suggests Toll and Imd pathways in the hemocytes of Spodoptera exigua. Partial Se-Toll-1 and Se-Relish-1 share high sequence homologies with known Toll and Relish genes of lepidopteran and dipteran species. Their expressions were detected from all developmental stages. In larval stage, there two genes were expressed in all tested tissues including hemocytes. Real time quantitative RT-PCR indicates that expression of both genes were highly up-regulated by bacterial and fungal infections. Various antimicrobial peptides (AMPs) were expressed in the hemocytes of S.exigua, in which their expressions appeared to be controlled by Se-Toll-1 and Se-Relish-1. However, Se-Toll-1 and Se-Relish-1 were proved to controlled different AMP genes from their RNA interference assays. These results suggest Toll and Imd signals in the hemocytes of S. exigua.