While light detection and ranging (lidar) was used as early as 1937 to measure atmospheric aerosol profiles, many applications only really became practical when searchlights were replaced by lasers as the light source. Since the first demonstration of laser based lidar in 1963, the number of applications in the atmosphere and oceans has grown tremendously. A Google search on “lidar” returns almost 15 million hits, ranging from basic research to commercial applications. With all of this activity, it seems surprising that so little has been done on the lidar detection of insects. Compared with aerosols, they have a very large lidar cross section.
In this paper, the authors demonstrated the utility of several lidar techniques to observe the distribution of damselflies in the wild. They used the depolarized elastic backscatter, based on the premise that damselflies are not spherical. Using the same 355-nm pulse, fluorescence receivers detected damselflies that had been caught and dusted with various dyes. The first technique provided information on the distributions of total numbers, while the second provided sex- and species specific information as different dyes were applied according to these criteria. Mosquitoes were also detected in the depolarized return and could be separated from damselflies by their lower return. The statistical analysis revealed a number of patterns. Both mosquitoes and damselflies were more active during periods of higher temperatures and lower winds; damselflies were more prevalent near reed stands; the males of one of the two species in the study area were more widely dispersed than either the females of that species or the males of the other species. These results clearly demonstrate the effectiveness of lidar for fine-scale studies of habitat use by insects.
The biosphere is rapidly changing under the influence of anthropogenic factors, and powerful new tools like this will be necessary to understand the full implications of those changes. Increased global travel has introduced new species into a number of ecosystems, occasionally disrupting existing ecological patterns. Rapid climate changes have also changed ecological patterns, as some species benefit at the expense of others. Insects are a critical part of any terrestrial ecosystem, whether it is pollinating or attacking plants, providing food for other animals, or spreading disease. The results of this paper suggest that lidar can be a valuable tool for understanding the interactions of flying insects with a changing environment so that deleterious effects can be mitigated.
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