Male and female visual neurones in dipterous insects [14]

In many insects some visually guided behaviour patterns differ between the sexes. For example, male hoverflies and houseflies chase females in the air using visual cues but are not chased by females^1-3. Presumably information processing by nerve cells also differs. The genetic and histochemical identification of a brain area in Drosophila that must be male for male behaviour to occur⁴ suggests that circuits for sexual behaviour are localised. Recent anatomical studies of houseflies (Musca domestica) have demonstrated certain visual neurones present only in males⁵. I report here results from another species (the blowfly, Calliphora erythrocephala) demonstrating another kind of sexual difference of neural architecture in the visual system. In this fly dimorphism is expressed by differences in the shapes of analogous neurones in males and females, as well as by the presence of some cells in only one sex. The sexually dimorphic neurones of both sexes 'view' a region of the visual field coinciding with the region of binocular overlap.