Nitric oxide (NO) is an immune mediator in several insects. In addition, eicosanoids mediate various immune responses in response to microbial challenges. This study focuses on cross-talk between two immune mediators. Nitric oxide synthase (SeNOS) of Spodoptera exigua was predicted in its cDNA sequence by interrogation to the transcriptomes and validated by RT-PCR against developmental stage and larval tissues. RNA interference (RNAi) of SeNOS suppressed nodule formation of S. exigua larvae against heat-killed Xenorhabdus hominickii. RNAi of SeNOS also suppressed NO levels in fat body and hemocytes along with suppression of PLA2 activity. NOS-specific inhibitor, L-NAME, also inhibited PLA2 activity, but its enantiomer, D-NAME, did not. However, PLA2 of dexamethasone or oxindole did not suppress NO levels in the immune tissues. In addition, X hominickii did not inhibit up-regulation of NO levels. These results suggest that NO signal activates PLA2 to produce eicosanoids to mediate immune responses

Phospholipase A2 (PLA2) catalyzes the committed step for eicosanoid biosynthesis. Two cellular PLA2 genes (iPLA2 and cPLA2) have been identified in Spodoptera exigua. PLA2 activity varied among developmental stages and different tissues. There was a positive correlation between PLA2 activities and their expression levels. Interestingly, there was significant inhibition by sPLA2 inhibitor, suggesting a presence of sPLA2 in S. exigua. An entomopathogenic bacterium, Xenorhabdus hominickii, infection suppressed expression of PLA2 genes and its extract inhibited enzyme activities. Oxindole of a bacterial metabolite of X. hominikii inhibited PLA2 activity and expression.

Integrin is a heterodimer protein that locates on cell membrane to interact with neighboring cells or extracellular matrix. A transcriptome analysis of the brassica leaf beetle, Phaedon brassicae, midgut identified both α and β subunits of integrin. RNA interference of β subunit genes significantly impaired survival of both larvae and adults of P. brassicae. A recombinant bacteria expressing double-stranded RNA specific to β integrin of P. brassicae were constructed and showed significant oral toxicities.