WEATHER ASSOCIATED WITH AUTUMN AND WINTER MIGRATIONS OF RICE PESTS AND OTHER INSECTS IN SOUTH-EASTERN AND EASTERN ASIA

Trajectory analysis was used to determine the direction and extent of windborne migrations of insects trapped in autumn and winter in south- east-and east Asia for 12 years between 1968 and 1987. Nearly 2600 tra jectories 12 ere drawn upwind at 10 m and 1.5 km from 15 catching site s and within the time (less than or equal to 60 h), wind speed (greate r than or equal to 5 km h(-1)) and temperature (greater than or equal to 10 degrees C) thresholds used, only 5% of the trajectories failed t o locate a possible source and over 90% were completed in 40 h or less . The delphacids Nilaparvata lugens Stal and Sogatella furcifera (Horv ath) dominated the trap catches (96%) with Cicadellidae (2.3%) and Dip tera (0.5%) as the nest most numerous. Very few Lepidoptera were repor ted (<0.3%). Nearly 80% of the trajectories were constructed in the pr evailing Winter Monsoon and Trade winds, resulting in a southward disp lacement of insects towards putative overwintering areas as reported i n previous studies. Tropical cyclones in autumn, produced trajectories which differed in both direction and extent from those in the prevail ing winds, supporting the suggestion that the contraction of the distr ibution areas of rice pests at this time of year is the product of a s eries of movements in different directions. The results suggest that m igrations continue throughout the year in the tropics and sub-tropics and indicate that this may be one way the capacity for long distance m igration is maintained in some rice pest populations.