Night flights of the Australian plague locust, Chortoicetes terminifera Walk., in relation to storms

Abstract

During long-term studies of the numbers of non-swarming C. terminifera, it was noted frequently that sudden changes in distribution and population densities occurred after storms. In most instances no flight was observed during the day rain fell or on the following day, but light trapping revealed considerable flight activity on nights after storms. Examples of night flight and associated changes in density are presented. It seems possible that C. terminifera requires higher humidities than those generally prevailing in the areas where it occurs, in order to undertake sustained flights. Hence there is an association between storms and night flights. The temperature threshold for flight is approximately 70�F. The airspeed of free flying C. terminifera in still air is 10 ft/sec and it is suggested that at night, in the absence of visual clues from the ground, flying locusts are likely to drift downwind at wind speeds well below their own airspeed. Drift of night-flying locusts in the air flowing behind fronts or flight activity in the zone of more humid air flowing from convective thunderstorms to places beyond the areas of rain are suggested to account for the occurrence of higher numbers of locusts in areas where rain has fallen.