A bug's life: diverse roles of insulin signaling in insect growth and development

Insulin signaling connects nutrient availability to the energy-consuming processes of growth and development throughout the animal kingdom. Insulin was discovered for its role in mammalian glucose homeostasis over one hundred years ago. Since then, research in diverse animals, and especially in insects, has vastly expanded our understanding of the myriad processes that insulin signaling regulates. Here, we focus on the developmental roles of the insulin signaling pathway in diverse insect species. Most insect genomes encode multiple insulin-like peptides (ILPs) and multiple insulin receptors. ILPs act in temporally specific ways to regulate tissue-specific processes, and in some cases, ILPs act with extreme specificity to control development. Our goal in this review is to highlight work in insects ranging from the fruit fly Drosophila melanogaster to mosquitoes, beetles, ants, and termites that illustrates these principles. Among these insects, insulin signaling regulates cell growth and proliferation, developmental timing, polyphenism, caste differentiation, and the very earliest stages of development via the production of healthy oocytes by adult female insects.