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 ground 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 parameters were measured continuously with weather station instrumentation, and radiosondes carried aloft by weather balloons were used to measure upper-air temperatures and wind conditions. Aerial volume density patterns and flight behaviors observed with radar varied nightly because of the many biological and meteorological variables involved, but certain seasonal characteristics of insect flight behavior became apparent during the course of the research. Nightly local dispersal flights at dusk were the norm, especially during the summer. Large numbers of insects were typically airborne for 1 to 2 h beginning about one-half hour after sunset with some of them reaching altitudes of 800 m or more where wind speeds were typically greater than 30 km/h. Several apparent long-range migration-type insect movement events were observed in which insects were concentrated in layers in high-speed, low-level wind jets that were apparently associated with nocturnal upper-air temperature inversions. Migration-type movement of insects tended to be south to north in the spring and early summer and north to south in the fall.