On Water-finding and Oviposition by captive Mosquitoes

Abstract

1. The behaviour of Anopheles labranchiae atroparvus, Culex pipiens molestus and Aëdes aegypti has been studied before and during oviposition.2. Anopheles and Culex when ready to lay make repeated descents to the ground and fly about with a skimming-hopping movement, while Aëdes flies about generally, at all heights.3. On encountering water Anopheles breaks into a hovering flight, laying its eggs during this “oviposition dance” or while settled on the water. Culex stops “dead” on the water and lays its eggs settled there, as does Aëdes but with some fidgeting about. After encountering water mosquitoes may leave it again, but fly about the floor more steadily and persistently than before.4. Among the factors which stimulate mosquitoes after they have arrived directly over a water surface, contact with the surface is essential for actual oviposition by Culex and Aëdes, and almost so for Anopheles. Good pre-ovipository responses may be induced by water vapour alone and by the reflection from the surface, although how this latter stimulus acts is not clear. A dark appearance, especially if the surroundings are relatively light, facilitates these responses.5. Direct attraction of the mosquitoes over the short range available in a cage was only induced by a contrastingly dark appearance, but Anopheles and Culex are aided in water finding by diurnal changes, correlated with light and activity changes, in the sense of their geotactic response.