A Simple Numerical Model of the Flight Behavior of Small Insects in the Atmospheric Convective Boundary Layer

We have combined aircraft and airborne Doppler radar observations to show that microinsects in the atmospheric convective boundary layer (CBL) are concentrated in rather welldeÞned plumes, that these plumes are generally found in thermals of rising air, and that the insects in those plumes oppose the updrafts at a rate that increases as the updrafts become stronger. In this paper, a simple numerical simulation of the airßow Þeld and insect concentration in the CBL is developed. The model shows a consistency of the observed insect ßight behavior with the presence of well-deÞned insect plumes in the otherwise well-mixed CBL and with the tendency of insects to cluster in updrafts. Themodel also explains the growth of insect plumes in themorning hours and their disappearance in the late afternoon. Other studies have proposed that the response of insects to being lofted high into the CBL is controlled by air temperature. Our simulation shows that a temperaturesensitive response alone does not yield well-deÞned plumes in regions of rising air currents. The observed ßight strategymay be counterintuitive, but we suggest that it has a clear adaptive advantage.