The Visual Responses of Flying Mosquitoes.

Summary. 1. Observations were made on females of the yellow‐fever mosquito, Aedes (Stegomyia) wgypti, which had not had a blood meal. 2. When suspended by a silk fibre they orientated inaccurately but consistently away from the source of an horizontal beam of artificial light. 3. They orientated accurately towards a vertical black stripe on a white background, and would rotate maintaining this position when the stripe was rotated around them up to 25 revolutions per minute. 4. Presented with two black stripes the mosquitoes faced one or other stripe, and not between the two. Light stimulation of the front part of the eye evoked a more powerful turning‐away response than stimulation of the sides. 5. The mosquitoes were attracted by and followed stripes which were moving, abandoning stationary similarly striped or darker walls to do so. 6. Unsuspended, freely flying mosquitoes in a wind tunnel orientated consistently up wind, keeping position or making headway as long as the background was visible, but not in darkness. Without a wind, but with transverse stripes moving along the floor, they flew with or ahead of the stripe movement, the visual equivalent of flying up wind. 7. The above evidence that up wind orientation involves a visual “compensation” mechanism is discussed, and a theory of the mechanism put forward. 8. The lateral ommatidia initiate the responses to light and to moving objects, working in a different way from the dorsal and ventral ommatidia, which are concerned in up wind orientation. Interplay between the two classes of response may take place. The work was carried out in the Department of Entomology of the London School of Hygiene and Tropical Medicine, during my tenure of the Avebury Studentship. I wish to thank Professor P. A. Buxton and all the members of his department, especially Dr. V. B. Wigglesworth, for their hospitality and fruitful suggestions.