The Response of Aquatic Insect Functional Groups to Polarized and Non-Polarized Light Pollution

Aquatic insects may be negatively impacted by the increasing nocturnal light pollution in populated areas adjacent to water sources. Smooth, dark surfaces can mimic water in the way they polarize light hitting the surface, creating an ecological trap for insects which rely on this cue for habitat selection and oviposition. These ecological light traps caused by unpolarized or visible light pollution often result in insect mortality and reproductive failure due to their dehydrating surfaces. Research has shown that functional groups of insects, such as predators or scavengers, are affected differently by visible light pollution, causing changes to community composition (Davies et al. 2012). However, less information has been collected on the impact of polarized light on aquatic insect functional groups, categorised by their ecosystem roles or trophic levels. Though it has already been shown that taxonomical groups respond differently to polarized light pollution (Kriska et al. 2009), a divergence across functional groups had not yet been looked at. The aim of this study was to determine the effect of light pollution on aquatic insect communities of tributaries in the Hudson Valley area. How either polarized light pollution or unpolarized light pollution affects specific functional groups of aquatic insects within an ecosystem had not yet been examined. In order to determine whether aquatic insects were more attracted to visible or polarized light pollution, and to what degree, a choice experiment was created at three levels of polarization. Using LED lights turned on at nightfall, at each polarization level, emerging insects would choose between a trap giving only a polarized light cue or one giving both a polarized and unpolarized light cue. Attraction to light traps did not differ across functional groups. However, insects were more attracted to trays that were 2 unshaded and producing both types of light cues. This study shows that aquatic insects are more attracted to both polarized and unpolarized light pollution than they are to only polarized light pollution. This synergistic effect is common at night, as artificial night lights provide the additional light source for polarization of reflective surfaces to occur. Because artificial polarizers are often made attractive and visible to insects due to man-made light sources, the effect of both light source and surrounding material is important to consider in riparian areas