Feeding behavior, particularly feeding motivation, is modulated by endocrine control in insects. The predominant endocrine factors capable of governing energy homeostasis to maintain nutrient-dependent regulation are Adipokinetic hormone (AKH) and Insulin-like peptide (ILP). AKH and ILP modulate the substantially constant sugar and lipid levels in the hemolymph. Interestingly those two hormones are also regulated by other peptide hormones by relaying the hormone stimulation from the disturbing nutritional condition. Endocrine factors secreted from several organs in insects that control gut contraction can also modulate feeding behavior. Together, systemic orchestration of endocrine factors is essential for precisely modulated normal feeding behavior in insects.
Most insects overwinter in a diapause state and some do as nymphs, but the molecular mechanism of the nymphal diapause remains largely to be explored. We analyzed the mechanism of nymphal diapause in the cricket Modicogryllus siamensis which occurs widely over Honshu and Kyushu. We found that day length and temperature regulate nymphal diapause in two separate ways, i.e., day length determines the number of molts and final body weight by controlling the JH synthesis system, while temperature controls the growth rate through the Insulin/TOR signaling system. In the field, short days and low temperatures during autumn and winter may reduce the nymphal growth rate and extend the nymphal period by extra-molts, allowing nymphs to live through the severe winter. Recent studies suggested that epigenetic regulation may be involved in the mechanism of photoperiodic determination of the development. We hope that the mechanism will be elucidated by using modern molecular biological techniques.