ARM radar and lidar data are used to study how insects move in the boundary layer - providing useful insights for agricultural pest forecast models.
In fine warm weather, the daytime convective atmosphere over land areas is full of small insects, among them serious pests to crops (e.g., some species of aphid), but also many beneficial species. Understanding how these insects move in the atmosphere is important for scientists developing forecast models to predict pest infestations on crops. Classic studies of insect flight behavior require intensive aerial trapping studies. In this study, scientists take advantage of radar and lidar instruments designed for meteorological studies of atmospheric motions, clouds, and aerosols. Flying insects also serve as scattering ‘targets’ for the radar and lidar beams, allowing the scientists to examine the motions of > 1 million insect targets.
This study reports on new observations of the vertical motion of insects with respect to the up- or downdrafts in convective boundary layers. The researchers find that insects are typically moving downwards through the downdrafts and are typically moving upwards when in the updrafts, but at a slower pace than the air itself. In updrafts, insects slow their ascent at a rate proportional to the updraft strength. The scientists also present a Lagrangian stochastic model of dispersion in convective boundary layers which contains a term accounting for the flight behaviors of aphid-type insects consistent with those emerging from the observational radar and lidar findings. Within this framework, the airborne dispersal of weak fliers may now be predicted more reliably on the basis of aerial density profiles and atmospheric physics. This holds promise for a new generation of precision pest forecast models driven by high resolution profiling data.
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, to determine generic behavioral responses to air movements shown by small day-migrating insects as a whole, the combination of millimeter-wavelength ‘cloud radars’ and Doppler lidar now provides virtually ideal instrumentation. In this study, scientists 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 Atmospheric Radiation Measurement (ARM) site in Oklahoma, USA. The scientists used co-located zenith-pointing Doppler lidar and Ka-band (8.6 mm wavelength) dual-polarized profiling cloud radar in July and August 2015. The combination of instruments provides unrivalled height- and time-resolved measurements of the vertical component of air velocity simultaneously with quantification of the movements of small insects. The resulting velocity measurements are interpreted in terms of the flight behaviors of small insects. These behaviors 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 characterizations of small insect aerial density profiles. The validated model represents a new way of linking insect density profiles in the convective boundary layer to individual flight behaviors, and thereby provides a modern context to classic studies based on results from aerial trapping. Understanding how flight behavior contributes to observed density profiles could, for instance, be used to relate numbers of airborne aphids caught by traps on different days, under different atmospheric conditions, to aphid densities available to colonize crops at local and regional scales.
Contacts (BER PM)
ARM Program Manager
Data were obtained from the Atmospheric Radiation Measurement (ARM) Climate Research Facility, a U.S. Department of Energy Office of Science user facility sponsored by the Office of Biological and Environmental Research. Rothamsted Research is a national institute of bioscience strategically funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC). Funding from a Marshall Sherfield Fellowship (P.M.S.) is gratefully acknowledged.
Wainwright, CE, PM Stepanian, DR Reynolds, and AM Reynolds. 2017. "The Movement of Small Insects in the Convective Boundary Layer: Linking Patterns to Processes," Scientific Reports, 7(1):5438. [doi:10.1038/s41598-017-04503-0]. (Reference link)
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