Circadian control of hatching in the cricket, Gryllus bimaculatus

The timing of hatching in the orthopteran Gryllus bimaculatus was examined under various lighting and temperature conditions. Eggs incubated in a 12 h light-12 h dark cycle at 25°C started to hatch 12 days after oviposition, and hatching occurred only within a limited portion or gate within the cycle, i.e. lights-off to shortly after lights-on. Gated hatching persisted in eggs transferred from the light-dark cycle to constant light or dark just before the start of hatching, while it did not appear in the population which had been kept in constant light immediately after oviposition. These results suggest that the gated hatching is controlled by a photoperiodically entrained circadian clock. The rhythm was evident when transferred to constant light after 10 days of exposure to the light cycle, but did not occur when transferred after 9 days of exposure to the light cycle or earlier, suggesting that the light cycle given around this stage is prerequisite to synchronized hatching. Ambient temperature also seems to work as a regulatory factor for this timing system, since the timing of the hatching peak changed within the gate dependent on the ambient temperature, being delayed with lower temperature.