Laboratory observations on the visual responses of tsetse flies

Abstract

The responsiveness of Glossina morsitans to a slowly moving visual stimulus was investigated under controlled environmental conditions. The stimulus consisted of a 4·5 em. wide vertical black stripe moving past a window at c. 12 em./sec. 12 times a minute. The flies were 30-90 em. distant from this window, and were exposed in groups of 10 (male or female) to the stimulus for 5 minutes, once every hour throughout the 12 hour light of a 24 hour light : dark cycle, from their last feed until incipient death. Responsiveness was measured as: (a) the percentage of flies taking-off, and (b) the total number of take-offs made, during the first 60 seconds of the stimulus (these 2 parameters are strongly positively correlated). Control observations were made hourly for 5 minutes in the absence of the stimulus.