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Abstract

Spectral sensitivity of the dorsal compound eye ofSimuliid males (Nematocera) shows a maximum in the u.v. at 340 nm, and a shoulder or second, smaller maximum around 430 nm. The visual pigment—based on retinal and therefore a rhodopsin—has its absorption maximum at 430 nm. The 340 maximum is due to a sensitizing pigment that transfers energy to the visual pigment. The properties of theSimuliid-photoreceptor hence are similar to most of the photoreceptors in higher flies (Musca, Calliphora, Drosophila), that also have a u.v.-absorbing sensitizing pigment. The difference is that inSimuliids the sensitizing pigment is not 3-hydroxyretinol as in the higher flies but a different substance, most likely retinol.