Desert locust, Schistocerca gregaria, eggs hatch in synchrony in a mass but not when separated

This laboratory study examined the stimuli involved in controlling egg hatching in the desert locust Schistocerca gregaria. We found that eggs that were kept in their egg pods hatched in synchrony, whereas those that were kept individually hatched over an extended period of time and took significantly longer to hatch. Synchronous hatching was also observed in pairs of eggs that were kept in contact with each other in the same plastic wells, but not in those that were kept individually in separate wells. This demonstrates that the eggs needed to be placed in contact with each other to achieve synchronous hatching and suggests that a hatching individual stimulates adjacent eggs to hatch via some unknown stimulus. Additional experiments suggested that neither auditory nor pheromonal stimuli were important in this process, but rather some sort of vibratory stimulus. This inference was supported by the results of another experiment, which demonstrated that when isolated eggs were vibrated with a vortex mixer, most of them hatched shortly after the stimulation. Our results suggest the possibility that direct mechanical stimulation caused by the first egg to hatch stimulates adjacent eggs to also hatch, thus producing synchronous hatching in the entire egg pod. However, the exact nature of this stimulus remains to be determined. Synchronous hatching is often observed in insects. It helps hatchlings to form aggregations and to reduce the risk of predation and cannibalism. Yet, the mechanism controlling this phenomenon has received little attention except for a few subsocial species. This study demonstrates that eggs kept in their egg pods hatched in synchrony, whereas those kept individually in sand hatched over an extended period of time and took longer to hatch. Synchronous hatching was also observed in pairs of eggs that were kept in contact with each other but not placed some distance apart from each other. We also show that artificial vibration induced hatching.