POPULATION-DYNAMICS OF THE AUSTRALIAN PLAGUE LOCUST, CHORTOICETES-TERMINIFERA (WALKER), IN CENTRAL WESTERN NEW-SOUTH-WALES .1. REPRODUCTION AND MIGRATION IN RELATION TO WEATHER

On three adjacent experimental plots in central western New South Wales, from 1971 to 1974, population fluctuations of the Australian plague locust were interpreted in terms of the interactions between reproductive rates (R0) between generations and net migration losses or gains (M±) within generations. Changes due to variations in net migration fluctuated over a greater range than those due to variations in reproductive rates, and were the major cause of the population fluctuations during the 16 generations studied. Variations in rainfall during breeding accounted for nearly 90% of the variance in reproductive rates, provided rain followed relatively dry periods. Changes caused by migration resulted from episodic, often long-range and generally southward displacements of adults at night in the gradient wind during disturbed weather. The frequency and intensity of migration depended primarily on the availability of potential emigrants and secondarily on the incidence of weather favourable for takeoff and prolonged flight. The incidence of rainfall before periods of migration was higher than expected. Adults thus migrated into areas already favourable for successful breeding. © 1979, CSIRO. All rights reserved.