1. This report continues the account of the experimental field work carried out by the Tsetse Investigation in Northern Nigeria from May 1926 up to the end of 1929. G. morsitans and G. tachinoides are the tsetse concerned. The main object of this work was to attempt to control tsetse by the destruction of primary and secondary foci by the clearing of all fringing forest, the general woodland being left untouched. Two main experimental areas have been dealt with, the Sherifuri area described previously and the Matyoro experimental area.

2. Methods of clearing and dealing with re-growth are described in detail. Records show that re-growth although very rapid the first year, then slows down to such an extent that it may not be economical to re-slash more often than every third year. The effect of clearing on tsetse was controlled by collecting fly week by week from certain fixed foci. These flies were dissected and the following factors noted : the sex proportion in the catch, the rate of catching, the state of nutrition, the proportion of very young flies, the blood content of the gut with classification of the kinds of blood found, and the trypanosome infection.

With G. morsitans, clearing of fringing forest only up to 800 yards from the collecting centre had no apparent effect on the wet season extension but at four miles it was reduced to one-sixth of its old figure.