The writer took over the Shinyanga fly-rounds in November 1934 from Mr. W. H. Potts, Senior Entomologist, under whose charge they had been since June 1932. The Maswa fly-rounds were not taken over until April 1935, when some of them had been in progress for a few months.

The Shinyanga area, its climate, topography, game and vegetation, have been described by Mr. H. M. Lloyd (1935), by Mr. C. F. M. Swynnerton (1923 and 1936), and by Mr. W. H. Potts in an hitherto unpublished paper, and no further general account is necessary. Table I gives in summarised form a synopsis of the seasons. The Maswa fly-belt lies to the east of the Shinyanga belt, separated from it by the Sukuma Cultivation Steppe, and was, until recently, part of the main G. swynnertoni belt that stretches from the bottom of the Serengeti Plains to Arusha and Moshi. As the result of reclamation measures carried out by the Tsetse Research Department during recent years, this belt has been severed from the main fly-belt, and the south-eastern section of this severed portion has again been cut off from the remainder by clearings. In this small isolated block of some 150 square miles an experiment in the exclusion of grass fires as a control measure against the tsetse was initiated in 1934, and fly-rounds were started in that area in order that a control might be kept on the progress of the experiment. Owing to administrative difficulties the experiment had to be discontinued in mid-1935, but the writer decided to continue the fly-rounds and to increase them by two additional rounds in the hopes of producing information, complementary and supplementary, to that from the Shinyanga rounds. The results of the fly-rounds from these two areas appear to throw light upon the vegetational preferences of G. swynnertoni and form the subject of this paper.