Rainfall-Evaporation Ratio in Relation to Locust and Grasshopper Outbreaks

Abstract

A WIDESPREAD outbreak of the migrating grasshopper, Chortoicetes terminifera, Walk., occurred in Australia during 1933–35. Reports show that, in South Australia, small, local swarms appeared during the summer 1932–33 in certain districts in the pastoral country about 150 miles north of the 10 in. annual isohyet (see Fig. 1). During 1933–34 swarms were widely distributed and in some areas extended about 100 miles south of this rainfall line. During 1934–35 they became generally distributed southwards over the agricultural areas of the State. These widespread invasions develop only at irregular intervals of several years; the presence of the insects in numbers, in the southern areas of the State, is temporary. Restricted outbreaks occur more frequently in certain areas situated immediately north of the 10 in. isohyet; in some instances the swarms may extend southwards into the wheat belt.