Extreme polarization sensitivity in the retina of the corn borer moth Ostrinia

Abstract

The visual system of the European corn borer (ECB, Ostrinia nubilalis) was analysed with microscopy and electrophysiological methods (ERG, single cell recordings). The ECB has a pair of mainly ultraviolet-sensitive ocelli and a pair of compound eyes, maximally sensitive to green light. The ommatidia contain a tiered, fused rhabdom, consisting of the rhabdomeres of 9-12 photoreceptor cells with sensitivity peak wavelengths at 356, 413, 480, and 530 nm. The photoreceptors in a large dorsal rim area have straight rhabdomeres and high polarization sensitivity (PS1,2=3.4, 14). Elsewhere, in the main retina, the majority of photoreceptors have non-aligned microvilli and negligible PS, but each ommatidium contains one or two blue-sensitive distal photoreceptors with straight microvilli parallel to the dorsoventral axis, yielding extremely high PS (PS1,2,3=56, 63, 316). Rhabdoms containing distal cells with potentially high PS have evolved at least two times, in moths (Crambidae, Noctuidae, Saturniidae) as well as in dung beetles (Scarabaeidae). The distal photoreceptors with high PS, sensitive to vertically polarized light, represent a monopolatic system which is unsuitable for the proper analysis of e-vector orientation. Anyhow, the distal photoreceptors might be used in conjunction with polarization-insensitive photoreceptors to detect objects that reflect polarized light with stereotyped orientation.