Nitiric oxide (NO) and eicosanoids function as crucial immune mediators in insects. This study focuses on cross-talkbetween two immune mediators in term of humoral immune response in Spodoptera exigua. Up-regulation of eight differentanti-microbial peptides (AMP) was observed against bacterial challenge. In contrast, injection of E. coli along with L-NAMEsignificantly down regulation the AMP production whereas D-NAME was not effective. The injection of E. coli withdexamethasone or SNAP also decreased AMP production whereas arachidonic acid (AA) compensated the dexamethasoneeffects. RNA inerferece against SeNOS showed the down-regulation of defensin mRNA level, whereas dsNOS injectionswith AA reversed the gene regulation.

The Riptortus (stinkbug) has a specialized symbiotic organ, M4 midgut, to harboring symbiont Burkholderia. M4 midgut is located in abdomen and surrounded with insect hemolymph. Recently our group demonstrated that symbiotic Burkholderia showed different physiology after adapting in M4 gut compare with in vitro cultured Burkholderia. And population of symbiotic Burkholderia in the M4 midgut is regulated by special organ. However, the molecular mechanism to prevent spreading and migrating symbiont bacteria to other host tissues from symbiotic organ is not clear. Therefore, we assumed that symbiont Burkholderia are susceptible to host humoral immunity after established infection in M4 midgut to prevent spreading and migrating into the other host tissues through Riptortus hemolymph. To prove this assuming, we tested the susceptibility and survival rate of symbiont Burkholderia in hemolymph of Riptortus in vitro and in vivo. We also examined the susceptibility of symbiont Burkholderia using purified antimicrobial peptides (AMP), pyrrhocoricin-like, thanatin-like and defensin-like AMPs. Finally, we tested inducing ability for AMPs by systemic infection of symbiotic Burkholderia. Gene expression of purified AMPs was not different after systemic infection of both symbiont and in vitro cultured Burkholderia. Surprisingly, in vitro cultured Burkholderia resisted on bacteria injected hemolymph and purified AMPs but symbiont Burkholderia were highly susceptible in bacteria injected hemolymph and purified AMP. These results suggest that symbiont Burkholderia can't survive in the hemolymph after escaping symbiotic organ. Moreover, humoral immunity of host Riptortus is important to prevent spreading and migrating symbiont Burkholderia into the other host tissue or organ from symbiotic organ.