Polarization Sensitivity in Tabanid Flies

Tabanid flies (horseflies further on; Diptera: Tabanidae) use polarization vision to seek water for oviposition, drinking and swarming, and for finding warm-blooded hosts for a blood meal. Visual guidance is provided by their compound eyes, which are built of two stochastically distributed ommatidial types. One type, homologue to fly ‘yellow’ ommatidia, is optimized to detect colour contrasts in the ultraviolet (UV) and green spectral range; the other type, homologue to fly ‘pale’ ommatidia, is optimized to detect polarized reflections in the UV and blue range. Polarized reflections are analysed by the inner photoreceptors R7 and R8, which have orthogonal and aligned rhabdomeres, sensitive to UV (R7) and UV-blue (R8) light. The two cells form a polarization-opponent pair, which is spectrally imbalanced and causes the horseflies to confound polarization and colour. The mechanism explains the mysterious attraction of biting flies towards blue objects (apart from the most attractive shiny black targets), which has been widely exploited for luring and trapping. The earlier literature about horsefly polarization sensitivity has been partly reviewed by Horváth and Csabai (Chapter 5: Polarization vision of aquatic insects. In: Horváth G (ed) Polarized light and polarization vision in animal sciences. Springer, Heidelberg/Berlin/New York, pp 113–146, 2014) and Horváth et al. (Chapter 22: Linearly polarized light as a guiding cue for water detection and host finding in tabanid flies. In: Horváth G (ed) Polarized light and polarization vision in animal sciences. Springer, Heidelberg/Berlin/New York, pp 525–560, 2014a; Chapter 23: Applying polarization-based traps to insect control. In: Horváth G (ed) Polarized light and polarization vision in animal sciences. Springer, Heidelberg/Berlin/New York, pp 561–584, 2014b).