Fly photoreceptors - II. Spectral and polarized light sensitivity in the drone fly Eristalis

Abstract

Eristalis tenax, the honeybee mimic, has photoreceptors mainly with double peaks as in typical flies, but the peaks are near 350 and 450 nm. Other cell types with peaks at 350 or 450 or 520 nm were encountered but not commonly. Measurements of the polarization sensitivity lead to the conclusion, as in Calliphora, that where there are two visual pigments they are separated in proximal and distal parts of the rhabdomere, with a twist between the two parts. Therefore there must also be two corresponding metarhodopsins. Receptors with a single spectral peak do not show this effect. Self-absorption can be excluded as an influence on spectral or polarization sensitivity. In its colour vision the drone fly is more like a typical fly than a bee but it has less green sensitive receptors and more blue sensitive ones than Calliphora.