WEATHER ASSOCIATED WITH SPRING AND SUMMER MIGRATIONS OF RICE PESTS AND OTHER INSECTS IN SOUTH-EASTERN AND EASTERN ASIA

Trajectory analysis of the windfields at 10m and 1.5 km was used to de termine the direction and extent of windborne movements of insects tra pped in spring and summer in south-eastern and eastern Asia for the pe riod 1968 to 1985. Approximately 2500 trajectories, depicting the move ments of airborne particles, were constructed where temperatures were high enough (>=10 degrees C) to allow flight and where wind speeds (> =5 kmh(-1)) were expected to lead to downwind displacements. Trap catc hes were dominated (97%) by delphacid species (e.g. Nilaparvata lugens St (a) over circle l and Sogatella furcifera (Horvath)), with Cicadel lidae (1.1%) and Diptera (0.7%) as the next most numerous. Very few Le pidoptera 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 confir med, as was the important role of frontal depressions in the windborne migration of insects in temperate areas. Nearly 50% of the trajectori es were constructed in mobile weather systems which both disturbed and strengthened the prevailing winds and led to pronounced differences i n the direction and distance of sources for insects caught at any catc hing site. Similarly, fluctuations in position of quasi-stationary fro nts induced considerable mixing of populations from different sources and influenced the northern extent of each phase of rice pest migratio n. The results supported earlier findings that migrations occurred bet ween the tropics and temperate areas during the spring and summer, but also indicated that migrations within the tropics at this time of yea r were a more frequent occurrence than had been considered previously.