Mayflies are least attracted to vertical polarization: A polarotactic reaction helping to avoid unsuitable habitats

Abstract

Like other aquatic insects, mayflies are positively polarotactic and locate water surfaces by means of the horizontal polarization of water-reflected light. However, may vertically polarized light also have implications for the swarming behaviour of mayflies? To answer this question, we studied in four field experiments the behavioural responses of Ephoron virgo and Caenis robusta mayflies to lamps emitting horizontally and vertically polarized and unpolarized light. In both species, unpolarized light induces positive phototaxis, horizontally polarized light elicits positive photo-and polarotaxis, horizontally polarized light is much more attractive than unpolarized light, and vertically polarized light is the least attractive if the stimulus intensities and spectra are the same. Vertically polarized light was the most attractive for C. robusta if its intensity was about two and five times higher than that of the unpolarized and horizontally polarized stimuli, respectively. We suggest that the mayfly behaviour observed in our experiments may facilitate the stability of swarming above water surfaces. Beside the open water surface reflecting horizontally polarized light, the shadow and mirror image of riparian vegetation at the edge of the water surface reflect weakly and non-horizontally (mainly vertically) polarized light. Due to their positive polarotaxis, flying mayflies remain continuously above the water surface, because they keep away from the unpolarized or non-horizontally polarizing edge regions (water surface and coast line) of water bodies. We also discuss how our findings can explain the regulation of mayfly colonization.

Method to improve the survival of night-swarming mayflies near bridges in areas of distracting light pollution

“…During their compensatory flight, the females use their polarization sensation to follow the horizontally polarizing track of the river. However, when they encounter a bridge or riverside, the horizontally polarized signal of the river is interrupted by the vertically polarized mirror image of the bridge or riparian vegetation [ 22 , 25 , 38 ]. Hence, the bridge as an optical barrier is able to interrupt the compensatory flight of both diurnal and nocturnal mayflies.…”

“…Several anecdotes, press reports and case studies have showed that illuminated boats and lamplit bridges overarching a river are major threats to nocturnal mayfly populations, like Ephoron virgo (Olivier, 1791) [ 22 ]. Huge mayfly swarms around illuminating street lamps were observed on the river Danube [ 22 – 25 ], Mississippi [ 26 ], Rhine [ 27 ], Main [ 28 ], at the Ardahan bridge on Kura river [ 29 ], bridge of Tudela on Ebro river [ 30 ] and bridge of Route 462 over the Susquehanna river, Pennsylvania [ 31 ]. According to Száz et al .…”

Quantifying the polarised light pollution of an asphalt road: an ecological trap for the stonefly,Perla abdominalis(Guérin-Méneville, 1838) (Plecoptera: Perlidae)

“…This mixing of the two components results in the decrease of the degree of polarisation. In cases, when the vertically polarised component overwhelms the surface-reflected light (e.g., when direct sunlight illuminates the water), the total water-returned light can be vertically polarised (Farkas et al 2016) as shown in Figures 2a-c. Thus, the angle of polarisation  of creek-reflected light depends on sunlight and shade conditions.…”

Insect Responses to Linearly Polarized Reflections: Orphan Behaviors Without Neural Circuits

“…One fly species, Halaeomyia petrolei even became adapted to a life near (or in the case of its larvae/pupae: inside) naturally occurring petroleum pools, feeding on arthropod prey that became trapped there (Thorpe, 1930 ). Female mayflies were shown to use horizontally polarized reflections off water to direct their so-called “compensatory upstream flights” before oviposition (Farkas et al, 2016 ) and this dispersion behavior is disrupted by (unpolarized) light pollution, for instance illuminated bridges (Szaz et al, 2015 ). In another example, female dragonflies attempted to lay eggs on an artificial, horizontally polarized surface, assuming it to be water (Wildermuth, 1998 ).…”