European farms at Abercorn had been suffering from bovine trypanosomiasis carried by Glossina morsitans Westw., and the Tanganyika Department of Tsetse Research were asked in 1935 to advise.

Fly-pickets were established in 1936 to prevent carriage of flies on to the farms, and a belt of country was protected from fire, with the object of thickening the woody vegetation so as to make it unfavourable to G. morsitans. The fire-protected area was extended and continued until 1946; serious escape fires occurred in 1938 and 1941. During these first five years the reduction in catches at the pickets was only about one-third.

An intensive survey of the area was made in 1941, as the result of which concentrations of flies were identified in certain shallow valleys forming the headwaters of small tributary streams. Several of these were cleared of trees, with the result that the apparent density of G. morsitans was at once depressed not only in the valleys themselves but over wide areas of untouched woodland round about.

In 1942 and the following years these clearings were extended to new valley sites as they were discovered, both inside and outside the fire-excluded area, and always with striking effects. The last clearing of all was done in 1952.