Hatching synchrony is controlled by a two-step mechanism in the migratory locust Locusta migratoria (Acrididae: Orthoptera): Roles of vibrational stimuli

The eggs of the migratory locust, Locust migratoria, hatch in synchrony from their pod. In this study, we examined the mechanism controlling hatching synchrony. Two eggs obtained from the same pod hatched in synchrony when kept in contact with one another, whereas those separated by a few millimeters hatched less synchronously. When a screen separated the eggs, the hatching was even more sporadic, indicating that hatching synchrony might be controlled by a two-step mechanism. We hypothesize that in the first step the embryos shortly before hatching control the time to enter a standby stage using some signal from neighboring eggs. The eggs in the standby stage hatch promptly when an additional stimulus is received from neighboring eggs. Before this stage, eggs cannot respond to that stimulus by hatching but may spontaneously hatch later. Introduction of a newly hatched nymph to single eggs 1 or 2 days before hatching advanced hatching of these eggs, but hatching occurred only sporadically. Eggs kept in contact with other eggs that had been killed by freezing shortly before hatching hatched as if they had been kept singly in separate containers, providing no evidence for involvement of chemical stimuli in controlling hatching synchrony. By contrast, eggs separated by several millimeters hatched as synchronously as those kept in contact with one another when they were connected by a piece of wire. Furthermore, vibrational stimulation derived from music greatly advanced hatching of separately kept eggs; however, hatching synchrony was not achieved unless the music started shortly before hatching. These results are consistent with the two-step hypothesis and indicated that locust embryos used vibrational stimuli from neighboring eggs for synchronous hatching.