Development of a desert locust plague

Abstract

THE role of phase change in the development of plagues of the desert locust, Schistocerca gregaria (Forskal), has been debated for many years^1–5. Much confusion has arisen because changes in behaviour, form and colour, which have all been used as indicators of phase status, do not proceed at the same rates. It is generally agreed, however, that behavioural changes are crucial in phase transformation. The subject at issue in the population dynamics of the desert locust is whether plagues, periods when extensive areas are infested by successive generations of gregarious populations, originate from an upsurge in numbers and associated transformation from the solitary-living to the gregarious state, or from successful breeding by gregarious populations postulated to survive continuously throughout the interplague recession periods³. Fundamental questions about the strategy of plague prevention depend on determining which of these hypotheses is correct^1,3,4,6.