Adaptive difference in daily timing of hatch in two locust species, Schistocerca gregaria and Locusta migratoria: The effects of thermocycles and phase polyphenism

•S. gregaria eggs hatched during the low temperature period of thermocycles.•L. migratoria eggs hatched during the high temperature period of thermocycles.•A temperature difference of 1 °C was sufficient for the locusts to respond.•The hatching timing was controlled by an endogenous mechanism.•The locust phase affected hatching time in S. gregaria but not in L. migratoria.

This study examined the effects of temperature and phase polyphenism on egg hatching time in the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria. The two species exhibited differences and similarities in hatching behavior when exposed to different temperature conditions. In 12-h thermocycles of various temperatures, the S. gregaria eggs hatched during the cryoperiod (low temperature period), whereas L. migratoria eggs hatched during the thermoperiod (high temperature period). The eggs of both species hatched during the species-specific period of the thermoperiod in response to a temperature difference as small as 1 °C. Furthermore, the locusts adjusted hatching time to a new thermal environment that occurred shortly before the expected hatching time. In both species, the hatching of the eggs was synchronized to a specific time of the day, and two hatching peaks separated by approximately 1 day were observed at a constant temperature after the eggs were transferred from thermocycles 3 days before hatching. Eggs laid by gregarious females hatched earlier than those laid by solitarious females in S. gregaria but this difference was not observed in L. migratoria.

Graphical abstractSchistocerca gregaria eggs hatched during the cryoperiod, whereas Locusta migratoria eggs hatched during the thermoperiod.Figure optionsDownload full-size imageDownload as PowerPoint slide