Abstract
The numbers of Glossina pallidipes Aust. and G. morsitans morsitans Westw. flying in and out of a large clearing in Zimbabwe were estimated from catches on unbaited electrified nets placed on the perimeter of the clearing. By estimating the numbers of flies that would encounter visual and olfactory attractants in the middle of the clearing, and from measurements of the numbers caught responding and estimates of the efficiency with which responding flies were caught, it was calculated that 80–100% of flying tsetse responded to stimuli they encountered. The importance of flight as a means of encountering host stimuli in woodland and open areas, and with mobile and stationary baits, is discussed.