Rainfall sequences leading to population increases of Austracris guttulosa (Walker) (Orthoptera: Acrididae) in arid north-eastern Australia

Abstract

In northern Australia, the spur-throated locust, Austracris guttulosa, has one generation per year with locusts surviving the dry season as immature adults. Adults lay after rain early in the wet season, mainly between October/November and January. On cracking clay soils, a fall of > 40 mm is required to allow oviposition, but to ensure survival of the resulting offspring, there must be follow-up rain of > 40 mm at the oviposition site within 6 weeks. Populations increase during years when more than 50% of the arid zone and Gulf receive both initial and two or more follow-up rains at intervals of ≤ 6 weeks. During the 1970s and 1990s, there were two periods of 3–5 years of such increase, and a large number of swarms resulted.