Four Insulin-Like Peptides Orchestrate Reproductive Signaling of the Green Lacewing, Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae)

Abstract In insects, insulin signaling plays a pivotal role in the regulation of growth, metabolism, reproduction, and aging. Revealing the regulatory roles of insulin signaling in natural enemy insects is helpful for developing artificial approaches to promote reproduction. In this study, the expression of four insulin-like peptides (ILPs) in female adults of the natural predator Chrysopa pallens was analyzed by quantitative real-time-polymerase chain reaction (qRT-PCR) and their functions were investigated by RNA interference (RNAi). C. pallens ILP1 (CpILP1) and C. pallens ILP4 (CpILP4) showed a gradual increase in mRNA levels from early adult stages to later stages. However, C. pallens ILP2 (CpILP2) and C. pallens ILP3 (CpILP3) had an opposite expression curve with a high transcript level at the beginning of the adult stage and a gradual reduction thereafter. All four CpILPs showed high expression levels in the ovary, but CpILP2 transcripts were also abundant in fat bodies. Disruption of CpILP1 and CpILP2 expression by RNAi-mediated knockdown strikingly suppressed ovarian development and reduced C. pallens vitellogenin gene 1 (CpVg1) transcripts. Depletion of CpILP3 transcripts did not significantly decrease ovariole number but drastically reduced CpVg1 expression. Interference with the expression of CpILP4 significantly inhibited ovarian development but did not suppress CpVg1 expression. All gene knockdowns failed to dramatically impair total fecundity and egg quality. These data suggest that the four C. pallens ILPs are involved in reproductive signaling at different degrees.