A forest ecosystem was divided into four zones: the original primary rain forest, secondary forest of short trees and bushes, tertiary Lantana thickets, and fallow plots. Tsetse, Glossina pallidipes Austen, were trapped in the four zones, dissected and the incidence of infection by the non-occluded virus determined. Tsetse density was relatively higher in the fallow land, and lowest in the primary forest. Virus infection was highest in the tsetse trapped in the primary forest (7%), and decreased progressively towards the fallow plots (1.8%). There were more young tsetse (less than 40-days-old) in the primary and secondary forests, whereas the Lantana thicket and fallow land had older flies (more than 40-days-old). Possible explanations of these observations are discussed.
