Analysis of the development of major plagues of the Australian plague locust Chortoicetes terminifera (Walker) using a simulation model

The development and decline of all the past major plagues of Chortoicetes terminifera in Australia has been analysed using all available locust data and a simulation model to estimate the course of events for periods when few locusts were reported. The model is based on the developmental biology of the locust and includes methods of estimating the duration of egg, nymphal and adult development and uses a pasture growth index and potential night displacement index to assess likely survival and migration. The analysis shows that five of the six plagues originated in the arid interior, where good spring and summer rain allowed two or three consecutive generations of successful breeding, before emigration to the agricultural country occurred in the late summer or early autumn. This is contrary to the idea held previously that most plagues developed from local breeding in established outbreak areas in the agricultural belt. The applications of these results, to improve population monitoring and control strategy by suggesting the best timing for surveys and when control would have most effect, are discussed.