SEASONAL RADAR AND METEOROLOGICAL OBSERVATIONS ASSOCIATED WITH NOCTURNAL INSECT FLIGHT AT ALTITUDES TO 900 METERS

Nocturnal aerial insect flight activities between 30 and 900 m above g round level were monitored with 3-cm scanning radar during the spring, summer, and fall seasons of 1988 and 1989 in the Brazos River Valley of Burleson County near College Station, TX. Surface meteorological pa rameters were measured continuously with weather station instrumentati on, and radiosondes carried aloft by weather balloons were used to mea sure upper-air temperatures and wind conditions. Aerial volume density patterns and flight behaviors observed with radar varied nightly beca use of the many biological and meteorological variables involved, but certain seasonal characteristics of insect flight behavior became appa rent during the course of the research. Nightly local dispersal flight s at dusk were the norm, especially during the summer. Large numbers o f insects were typically airborne for 1 to 2 h beginning about one-hal f hour after sunset with some of them reaching altitudes of 800 m or m ore where wind speeds were typically greater than 30 km/h. Several app arent long-range migration-type insect movement events were observed i n which insects were concentrated in layers in high-speed, low-level w ind jets that were apparently associated with nocturnal upper-air temp erature inversions. Migration-type movement of insects tended to be so uth to north in the spring and early summer and north to south in the fall.