Many holometabolous insects hibernate by triggering diapause, an “actively-induced” dormancy that blocks developmental functions. Yet, the nature of signals enhancing the plasticity of developmental system and underlying diapause inducibility is still elusive. We show that the “Insulin/IGF” dilp2/5 genes, encoding for developmental hormones, antagonize diapause switch in D. melanogaster and their modulation is pivotal in sensitizing the developmental system to environmental perturbations. Functional impairment of dilp2/5 signaling results in the appearance, or inhibition, of the inducible diapause polyphenism, revealing that they are at the core of the gene network regulating diapause inducibility, beyond the control of developmental time. DILP2/5, as dispensable developmental hormones, cover a latent and hidden plasticity of development, underlying the evolution of an inducible diapause polyphenism through genetic accommodation. Such hormonal mechanism might be the putative target to bioengineer diapause inducibility
