Two experiments are described where applications of coarse aerosols have been made to areas of savannah woodland infested with tsetse flies (Glossina spp.).

The applications were made at nominal dosages of 0·25 gallons per acre, which was equivalent to either 0·20 lb. of p.p′DDT per acre, or 0·03 lb. of γ BHC per acre. The coarse aerosols had mass median diameters of approximately 60 microns.

In one experiment, carried out at Urambo, Tanganyika, a reduction of 95 per cent, was obtained in populations of G. morsitans Westw. This kill was somewhat lower than in many other experiments, a fact that can be attributed mainly to our inability to maintain the cycle of applications. Immigration of flies into the treated area caused a relatively rapid increase in fly numbers to levels comparable to the pre-treatment populations, and in this respect the experiment was a failure.

The other experiment, in Lango County, Uganda, was highly successful, and reduced a population of G. morsitans to 0·05 per cent, of its pre-treatment level, and eradicated a small population of G. pallidipes Aust. It is indeed likely that no stable population now exists in the area, and that the very few flies caught there since the end of the applications have been wanderers from other infested woodland. The continued success of the experiment is considered to be due to the effective isolation of the area.

Some brief comments are made upon the costs of the method, and on its value under conditions of land development in Africa.