A tsetse-control trial was carried out in a primary forest habitat on Unguja Island of Zanzibar to assess the effect of insecticide-impregnated blue cotton screens on a population of Glossina austeni Newstead. In November 1991, screens were deployed at densities of 45–70 per km2 and the fly population was monitored monthly using sticky panels. Both female and male daily catches were not affected during the initial five months after screen deployment, but the physiological age distribution of female flies shifted significantly towards younger groups. Females were more influenced by the screens than males. The fly population was very low after the long rainy season, but increased to pre-control levels three months after the flooding of the forest floor. Thereafter, male and female apparent densities decreased, and 78–91% and 98–99% suppression was obtained for males and females respectively at the end of the 18-month intervention period. While effective control of G. austeni using blue cotton screens was shown to be feasible, it required a high deployment density and a long intervention period.
