Insect blood cells (hemocytes) play a key role in defense against parasites and other pathogenic organisms that infect insects. Cellular immune responses exhibited by hemocytes are acute and effective to initially suppress pathogenic processes. Subsequently humoral immune responses executed by antimicrobial peptides completely cleared the pathogens with help of hemocytes. Two immune mediators, plasmatocyte-spreading peptide (PSP) and eicosanoid, are known to mediate cellular immune responses by activating hemocyte behavior. This study was focused on how these two immune mediators work together to express hemocyte spreading behavior. Both PSP and prostaglandins stimulate hemocyte spreading in dose-dependent manners in the beet armyworm, Spodoptera exigua. Interstingly, inhibition of eicosanoid biosynthesis inhibited PSP activity on mediating the hemocyte-spreading behavior. However, the addition of eicosanoid biosynthesis precursor, arachidonic acid, rescued the hemocytespreading activity. Inhibition of PSP or its receptor by each RNA interference are now under investigation to test whether PSP triggers eicosanoid signaling. These results suggest that there is a cross-talk between PSP and eicosanoid to express hemocyte-spreading behavior in response to bacterial challenge