Hatching synchrony in solitarious and gregarious locust eggs

Abstract Synchronous hatching is widespread in insects and may confer adaptive advantages such as predator avoidance and aggregation of hatchlings. In Locusta migratoria , two mechanisms have been proposed to underlie hatching synchrony within egg pods: maternal phase effects and embryo–embryo interactions. This study examined whether maternal phase influences within‐pod hatching synchrony when embryo–embryo communication is experimentally manipulated. Eggs from solitarious and gregarious females were maintained either in contact (clumped) or individually separated and incubated at 30°C under continuous illumination. Mean hatching time, within‐batch variance in hatching time, and the duration from 10 to 90% hatching were analyzed. Gregarious eggs laid by crowd‐reared adults were slightly larger and hatched earlier on average than solitarious eggs laid by isolation‐reared adults under both egg conditions, confirming a phase‐dependent difference in embryonic developmental rate. In contrast, hatching synchrony was strongly influenced by egg condition: Most clumped eggs hatched within a few hours, whereas separated eggs hatched later and over a much broader time span. No significant phase‐dependent differences were detected in either the variance of hatching time or the 10–90% hatching period. These findings indicate that maternal phase primarily influences embryonic developmental rate, whereas physical contact among eggs is essential for the final synchronization of hatching within an egg pod. The results highlight the importance of distinguishing embryonic developmental timing from within‐pod hatching synchrony.