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

In northern Australia, the spur-throated locust, Austracris guttulosa, has one generation per year with locusts surviving the dry season as immature a dults. Adults lay after rain early in the wet season, mainly between Octobe r/November and January. On cracking clay soils, a fall of > 40 mm is requir ed 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 w eeks. 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 less than or equal to 6 weeks. During the 1970s and 1990s, there were t wo periods of 3-5 years of such increase, and a large number of swarms resu lted.