The movement of small insects in the convective boundary layer: linking patterns to processes

Abstract

In fine warm weather, the daytime convective atmosphere over land areas is full of small migrant insects, among them serious pests (e.g. some species of aphid), but also many beneficial species (e.g. natural enemies of pests). For many years intensive aerial trapping studies were the only way of determining the density profiles of these small insects, and for taxon-specific studies trapping is still necessary. However, if we wish to determine generic behavioural responses to air movements shown by small day-migrating insects as a whole, the combination of millimetre-wavelength ‘cloud radars’ and Doppler lidar now provides virtually ideal instrumentation. Here we examine the net vertical velocities of > 1 million insect targets, relative to the vertical motion of the air in which they are flying, as a succession of fair-weather convective cells pass over the recording site in Oklahoma, USA. The resulting velocity measurements are interpreted in terms of the flight behaviours of small insects. These behaviours are accounted for by a newly-developed Lagrangian stochastic model of weakly-flying insect movements in the convective boundary layer; a model which is consistent with classic characterisations of small insect aerial density profiles. We thereby link patterns to processes.

Environmental effects on flying migrants revealed by radar

“…A consequence of solar radiation is the formation of thermal convection in the diurnal boundary layer, which is exploited by diurnally-migrating insects and birds. Soaring landbirds are the most evident example of adaptation to such atmospheric phenomenon (Spaar and Bruderer 1996), but also smaller migrants such as aphids and several butterfly species use thermal updrafts to gain altitude during their migratory flights (Schaefer 1976, Wainwright et al 2017.…”

Windborne migration of Auchenorrhyncha (Hemiptera) over Britain

“…This characteristic, together with the sampling height, indicates that all individuals caught were actively migrating rather than being accidently caught up in convective up-draughts. In fact, small insects aloft in daytime convective conditions display distinctive behaviours with respect to the air column in which they are fl ying (Wainwright et al, 2017).…”

“…This may well be because nocturnal air temperatures in Britain and northern Europe are often below thresholds for fl ight (Raatikainen, 1967;Raatikainen & Vasarainen, 1973), but daytime fl ight does have the advantage that, during sunny weather, migrants can utilise convective lift to gain height, thus reducing power consumption needed for migratory fl ight. As mentioned above, many small migratory insect taxa are similarly adapted (Wainwright et al, 2017).…”

Characterizing animal anatomy and internal composition for electromagnetic modelling in radar entomology

“…, ; Wainwright et al. ). In parallel efforts in the atmospheric sciences, airborne insects were also detected by early meteorological research radars and, after initial controversy over their biological origin (see Chapt.…”

“…scanning, profiling, transecting and tracking), wavelengths and transmitter powers have been used in hundreds of entomological research studies (over 250 publications containing significant radar entomology content are listed on the Radar Entomology Website [http://radarentomology.c om.au/bibliography/]). Many of these studies have used specially developed 'entomological' radars (Drake and Reynolds 2012), which have acquired quantitative estimates of insect activity unobtainable by any other means, and revealed unanticipated behavioral phenomena (e.g., Hu et al 2016;Reynolds et al 2016Reynolds et al , 2017Wainwright et al 2017). In parallel efforts in the atmospheric sciences, airborne insects were also detected by early meteorological research radars and, after initial controversy over their biological origin (see Chapt.…”