The Influence of Rainfall on the Densities of Adult Chlortoicetes Terminifera (Walker) in Central Western New South Wales, 1965-73.

Abstract

The densities of adults of the Australian plague locust (Chortoicetes terminifera (Wlk.) were estimated in a network of permanent plots in part of the Bogan-Macquarie outbreak area from 1965 until early 1973. In that area, 2-3 generations are produced between September and April-May, depending on rainfall. C. terminifera is able to maintain a high rate of reproduction in this area. The numbers of adults produced in one generation are directly related to the total rainfall during a period of three weeks at the time of hatching and can be predicted by a linear regression of adult numbers on rainfall. The evidence suggests that rain favours the survival of nymphs immediately after hatching by influencing the growth of food-plants. The ecological factors that cause discrepanices between the observed numbers and those predicted by regression are discussed. Among these are immigration, qualitative changes such as the development of hopper bands and the build-up of natural enemies, combined with errors in the selection of suitable oviposition sites by the locusts themselves. Despite intermittent droughts, the range of fluctuation of numbers of C. terminifera is limited in this region, and in the long term average numbers are high.