Experiments in the Control of Tsetse-fly. (Report of the Tsetse Investigators in N. Nigeria.)

Abstract

(1) This report is an account of the experimental work carried out by the Tsetse Investigators in Northern Nigeria during the period from January 1924 to May 1926. G. morsitans and G. tachinoides are dealt with. In the Introduction the district around Sherifuri, where the camp is situated, is described, the differences between primary and secondary tsetse foci are defined, and an account is given of the method of collecting data as a basis on which to estimate the effects of experiment. Before and during experiment flies were collected week by week from foci subject to experimental change and from others employed as controls, the following factors being 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 guts with classification of the kinds of blood taken, and the trypanosome infection.(2) An experiment was carried out in which game was excluded from a good secondary focus of tsetse by means of a fence. This set up a state of starvation in morsitans and to some extent in tachinoides. There was a marked reduction in the abundance of both species, especially in morsitans. More blood than usual was taken by morsitans from birds, and both species contained a larger proportion of blood of human type than is usual. Invasion of the enclosed area by tsetse from outside vitiated the experiment and resulted in certain anomalies, viz., that the rate of trypanosome infection remained high ; the blood content was not appreciably decreased ; the proportion of very young flies increased abnormally in morsitans. It is considered that game destruction, if it could be accomplished, would lead to a disappearance of morsitans, but not of tachinoides, and for this reason no policy of game destruction is recommended, but a policy of laissez faire towards the game in Northern Nigeria, so that there may be no increase in the wild Ungulata, which results in increase and spread of fly.(3) A successful experiment in deferred grass burning is recounted. The late sweeping fire resulted in a great mortality of morsitans and tachinoides, both flies and pupae. It hardly affected the growth of established thicket, but probably checked expansion of such and the formation of new thicket. It is considered that late grass fires, well organised, might have a good effect in Northern Nigeria, but the difficulties in the way of postponement of burning are exceedingly great in this country.(4) The commencement of an experiment in clearing with subsequent settlement is briefly described. Except on the main road through the experimental area only fringing forest is being cut down, the general woodland being left untouched. If this policy is successful only a relatively small proportion of a fly area will need to be cleared, attention being confined to the main foci.(5) An account is given of an unsuccessful attempt to introduce into Nigeria Syntomosphyrum glossinae, a Chalcid parasite of G. morsitans in East Africa.