Phototaxis and polarotaxis hand in hand: night dispersal flight of aquatic insects distracted synergistically by light intensity and reflection polarization |
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Authors: | Pál Boda Gábor Horváth György Kriska Miklós Blahó Zoltán Csabai |
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Institution: | 1. Department of Tisza River Research, MTA Centre for Ecological Research, Bem tér 18/c, Debrecen, 4026, Hungary 2. Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, E?tv?s University, Pázmány sétány 1, Budapest, 1117, Hungary 3. Group for Methodology of Biology Teaching, Biological Institute, E?tv?s University, Pázmány sétány 1, Budapest, 1117, Hungary 4. Danube Research Institute, MTA Centre for Ecological Research, Alkotmány út 2-4, Vácrátót, 2163, Hungary 5. Department of Hydrobiology, Institute of Biology, Faculty of Sciences, University of Pécs, Ifjúság útja 6, Pécs, 7624, Hungary
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Abstract: | Based on an earlier observation in the field, we hypothesized that light intensity and horizontally polarized reflected light may strongly influence the flight behaviour of night-active aquatic insects. We assumed that phototaxis and polarotaxis together have a more harmful effect on the dispersal flight of these insects than they would have separately. We tested this hypothesis in a multiple-choice field experiment using horizontal test surfaces laid on the ground. We offered simultaneously the following visual stimuli for aerial aquatic insects: (1) lamplit matte black canvas inducing phototaxis alone, (2) unlit shiny black plastic sheet eliciting polarotaxis alone, (3) lamplit shiny black plastic sheet inducing simultaneously phototaxis and polarotaxis, and (4) unlit matte black canvas as a visually unattractive control. The unlit matte black canvas trapped only a negligible number (13) of water insects. The sum (16,432) of the total numbers of water beetles and bugs captured on the lamplit matte black canvas (7,922) and the unlit shiny black plastic sheet (8,510) was much smaller than the total catch (29,682) caught on the lamplit shiny black plastic sheet. This provides experimental evidence for the synergistic interaction of phototaxis (elicited by the unpolarized direct lamplight) and polarotaxis (induced by the strongly and horizontally polarized plastic-reflected light) in the investigated aquatic insects. Thus, horizontally polarizing artificial lamplit surfaces can function as an effective ecological trap due to this synergism of optical cues, especially in the urban environment. |
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