Hatching rhythms in the desert locust, <i>Schistocerca gregaria</i>

Abstract

ABSTRACT. The eggs of Schistocerca gregaria (Orthoptera, Acrididae) incubated under natural conditions hatch only within a few of hours on either side of dawn. This gated hatching is controlled by a circadian clock that is phase set by the diel fluctuations in the temperature of the soil surrounding the eggs. There is a circadian fluctuation in haemolymph sugar concentration which is initiated at least 4 days before hatching. However, eggs hatch arrhythmically unless given cycled temperature incubation for at least 10 days of a 12–13‐day incubation. Increase in acetylcholine esterase content of the brain during the penultimate day suggests that increased hatching rhythmicity occurring at this time is the result of increased neural organization. Embryonic activity and respiration show no circadian rhythm but do provide confirmatory evidence of a quiescent phase prior to hatching. This quiescent phase is an integral part of gated hatching behaviour.