Antimicrobial peptide cecropin B functions in pathogen resistance of .

(Lepidoptera: Noctuidae) is an omnivorous pest that poses a great threat to food security. Insect antimicrobial peptides (AMPs) are small peptides that are important effector molecules of innate immunity. Here, we investigated the role of the AMP cecropin B in the growth, development, and immunity of . The gene encoding cecropin B () was cloned. The expression of was determined in different developmental stages and tissues of . It was highest in the prepupal stage, followed by the pupal stage. Among larval stages, the highest expression was observed in the fourth instar. Tissue expression analysis of fourth instar larvae showed that was highly expressed in the fat body and haemolymph. An increase in population density led to upregulation of expression. expression was also upregulated by the infection of third and fourth instar with or (). RNA interference (RNAi) targeting inhibited the emergence rate and fecundity of , and resulted in an increased sensitivity to and . The mortality of larvae was significantly higher in pathogen plus RNAi-treated than in controls treated with pathogens only. Our findings indicate that functions in the eclosion and fecundity of and plays an important role in resistance to infection by and .