Zoological Science

Abstract

In polarization-sensitive insect species an orthogonal arrangement of photoreceptive microvilli is a characteristic feature. However, mosquito eyes had not revealed this feature, and polarization sensitivity (PS) was considered to be non-existent in them. Recently, however, gravid Aedes (Stegomyia) aegypti females were found to possess PS, sequels of which could be demonstrated only in the absence of chemicals emitted by conspecifics. Therefore, PS in Ae. aegypti, unlike that of other aquatic insects, apparently does not play a dominant role in locating water bodies, and is difficult to demonstrate in situations free of chemical cues. Here, we present behavioral evidence with Ae. aegypti females, exposed to large-field optomotor stimuli based solely on polarization contrast. Under conditions with stripes of alternating orthogonal directions of polarization, clear optomotor responses were elicited, no different from those in response to a rotating drum with vertical black and white stripes. Thus, Ae. aegypti is indeed polarization-sensitive; it reacts to vertically-striped contrast patterns with low spatial frequency on the basis of both intensity and polarization differences between the stripes.