Weather associated with spring and summer migrations of rice pests and other insects in south-eastern and Eastern Asia

Abstract

AbstractTrajectory analysis of the windfields at 10 m and 1.5 km was used to determine the direction and extent of windborne movements of insects trapped in spring and summer in south-eastern and eastern Asia for the period 1968 to 1985. Approximately 2500 trajectories, depicting the movements of airborne particles, were constructed where temperatures were high enough (>=10°C) to allow flight and where wind speeds (> =5 kmh−1) were expected to lead to downwind displacements. Trap catches were dominated (97%) by delphacid species (e.g. Nilaparvata lugens Stål and Sogatella furcifera (Horváth)), with Cicadellidae (1.1%) and Diptera (0.7%) as the next most numerous. Very few Lepidoptera were reported. Most trajectories were less than or equal to 40 h in duration. The previously recognized northwards migration along a broad front in prevailing Summer Monsoon and Trade winds was confirmed, as was the important role of frontal depressions in the windborne migration of insects in temperate areas. Nearly 50% of the trajectories were constructed in mobile weather systems which both disturbed and strengthened the prevailing winds and led to pronounced differences in the direction and distance of sources for insects caught at any catching site. Similarly, fluctuations in position of quasi-stationary fronts induced considerable mixing of populations from different sources and influenced the northern extent of each phase of rice pest migration. The results supported earlier findings that migrations occurred between the tropics and temperate areas during the spring and summer, but also indicated that migrations within the tropics at this time of year were a more frequent occurrence than had been considered previously.