Each year the Mythimna separate (Walker), undertakes a seasonal, long-distance, multigeneration roundtrip migration between southern and northern China. Despite its regularity, the decision to migrate is facultative, and is controlled by environmental, physiological, hormonal, genetic, and molecular factors. Migrants take off on days 1 or 2 after eclosion, although the preoviposition period lasts ≈7 d. The trade-offs among the competing physiological demands of migration and reproduction are coordinated in M. separata by the "oogenesis-flight syndrome." Larvae that experience temperatures above or below certain thresholds accompanied by appropriate humidity, short photoperiod, poor nutrition, and moderate density tend to develop into migrants. However, there is a short window of sensitivity within 24 h after adult eclosion when migrants can be induced to switch to reproductive residents if they encounter extreme environmental factors including starvation, low temperature and long photoperiod. Juvenile hormone (JH) titer is low before migration but high titers are associated with termination of migratory behavior and the switch to reproduction. Early release of JH by the corpora allata in environmentally stressed 1-d old adults, otherwise destined by larval conditions to be migrants, switches them to residents. Offspring inherit parental additive genetic effects governing migratory behavior. However, they also retain flexibility in expression of both flight and reproductive life history traits. The insect neuropeptide, allatotropin, which activates corpora allata to synthesize JH, controls adult flight and reproduction. Future research directions to better understand regulation of migration in this species are discussed.

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The first day of adult life is the sensitive stage for shifting migrants into the resident morphs of the oriental armyworm (OAW), Mythimna separata (Walker). The juvenile hormone (JH) titer, expression of the allatotropin (AT) gene, and their relationship were investigated in adult female migrants starved in the sensitive stage, to understand the underlying mechanism of changing migrants into resident OAWs. Haemolymph JH titers of the starved female adults were mostly elevated earlier than in controls, although not all differences were statistically significant. JH I titers in the starved moths were significantly higher than those in the controls on 1, 2, and 5 days after treatment (DAT), respectively. JH II titers in the starved moths were significantly higher than the controls through the period tested except on 5 DAT. JH II is the most likely regulator in changing migrants into resident morphs. The relative quantities of AT expression in the starved moths were higher through the period tested except on 5 DAT. AT expression and JH titers appear to be positively correlated, especially for those in earlier days of the adult life. We infer that AT is the important regulator of JH levels. A model for the shifting of migrants into resident morphs in the OAW is proposed.