Before a hornworm transitions from the pupal stage to the adult stage and becomes a moth, a broad spectrum of behavioral, physiological, and developmental processes take place, including several molts from the first larval instar to its last. The majority of these processes are induced and regulated via cascades of biochemical reactions within the insect's body.
The major actors in these biochemical cascades include hormones (intercellular messaging proteins derived from the endocrine system - think slower), neurohormones (intercellular messaging proteins derived from neurosecretory cells - think faster), enzymes, and the tissues/organs these molecules interact with. Among the myriad biochemical pathways that have been described and the countless processes yet to be discovered, one of the most well-understood biochemical mechanisms is that which controls molting in insects and crustaceans (Covi et al. 2012).