On the sexual maturation, breeding, and ovipsition behaviour of the Australian plague locust, Chortoicetes terminifera (Walk.).

Abstract

From samples taken at regular intervals from populations of Chortoicetes terminfera (Walk.), it was found that the time of onset of sexual maturation in the female was consistently associated with a sharp drop in daily air temperature and not invariably with rainfall. As such temperature changes are indicative of air mass changes and the occurrence of cold fronts, the locusts began to mature with, or just prior to, rain. The period required for maturation was approximately 12 days and the frequencies of occurrence of gravid females in populations underwent cyclic fluctuations. It is, therefore, possible to predict the time of laying from a knowledge of the time of onset of maturation. Moreover, the sequence of successive layings in populations could be determined from cosine curves with periods of 12 days. Females of the second generation of the locust "season" (January-March) laid more egg pods than those of the first generation (September-December of the previous year). This may partly explain the frequent occurrence of temporary declines in swarm numbers and the collapse of outbreaks during the January-February period. In both swarming and non-swarming populations synchronization in the time of completion of a cycle of maturation by females was poor. However, the social behaviour of gregarious populations ensures that the egg pods laid by females of different physiological ages, i.e. those that reached maturity on different days, are concentrated in the one oviposition site. This maintains continuity in the swarming cycle because concentration of the egg pods results in the subsequent crowding of the nymphs during the hatching period.