New insights into insulin-signaling pathway in hibernating Colorado potato beetle, Leptinotarsa decemlineata

Insulin signaling has a pivotal role in metabolism and growth in mammalians. Likewise, the insulin signaling pathway and downstream elements regulate development and reproduction in insects. Insulin signaling is also known as one of the main regulators of hibernation in insects as it is involved in the metabolic switch to lipid storage, thereby enhancing the post-hibernation survival. However, the knowledge on the regulation of diapause initiation and maintenance via the insulin signaling pathway is poor. In the current study, we investigated the role of insulin signaling in the initiation and maintenance phases of the hibernating Colorado potato beetle, Leptinotarsa decemlineata, a destructive pest of potato plants worldwide. Through a laboratory-based simulation model, the larvae were exposed to short day light upon egg hatching to induce diapause, and diapause-destined larvae, and adults under diapause or emerged from diapause were monitored for the expression profile of major genes of insulin-signaling pathway [ insulin-like peptides (ILPs), insulin-like peptide receptor (ILPR) and FOXO] and energy metabolism parameters (total triglyceride and trehalose levels) in comparison to control. The corresponding samples were also examined for the structure of their fat body (lipid droplets) via microscopic investigation. Overall, insulin signaling is a principal pathway of diapause initiation and maintenance in L. decemlineata; however, further studies would elucidate the exact role of this pathway in diapause.