The distribution of the Fusca group of tsetse flies (Glossina) in Nigeria and West Cameroun.

Abstract

A short history of the study of the six tsetse species of the group of Glossina fusca (Wlk.) that occur in Nigeria and the former British Southern Cameroons (now West Cameroun, part of the Federal Republic of Cameroun) is given. Extensive collections of these species were not made until after the scheme for the establishment of the West African Institute for Trypanosomiasis Research was initiated in 1947. More intensive studies, stimulated by the discovery of a technique of searching for the flies in their resting sites, were carried out in southern Nigeria, at the W.A.I.T.R. Field Station and elsewhere, from 1953 onwards.The situation, climate and vegetation zones of Nigeria are described. Species of the fusca group occur only in the southern part of Nigeria and in West Cameroun and depend on some type of forest vegetation, ranging from relatively dry forest islands and riverine forest in savannah to dense, humid, wet rain forest, for their habitat. Rainfall and relative humidity, in general, decrease with increasing distance from the coast and are factors of great importance in determining the distribution of the fusca group.Locality records for each species of the fusca group are listed according to the Province and nearest town or village to the place where they were collected, and the results are shown on maps. G. medicorum Aust. has only been recorded from the relatively dry northern part of the rain forest and forest islands or riverine forest in savannah in Western Nigeria. G. nashi Potts occurs in dense, wet rain forest in West Cameroun. G. tabaniformis Westw. occurs, especially, in forest reserves in Ondo and Benin Provinces of Western Nigeria and in wet rain forest in West Cameroun and adjoining forest country in Eastern Nigeria. G. haningtoni Newst. & Evans is common in wet rain forest in West Cameroun and there are also records 175 miles to the west in Delta Province of Western Nigeria. G. fusca occurs in a wider range of climatic conditions and habitat types than the other species; it has been recorded in vegetation varying from forest islands in savannah to wet rain forest. G. nigrofusca Newst. is a rare but widespread species in Nigeria and West Cameroun where it occurs typically in wet rain forest.The dry and wet limits (indicated by mean annual rainfall) of the distribution of each species in Nigeria and West Cameroun are given, and the importance of climate, especially humidity, in determining these distributions is discussed. The climatic requirements of the six species are confirmed by their distribution outside the boundaries of Nigeria and West Cameroun. G. medicorum extends mainly to the west of Nigeria although there are also two records of the species from Gabon, widely separated from the main area of distribution of the species in West Africa. G. haningtoni and G. nashi, species typical of Central Africa (as here defined), extend only to the east and south of Nigeria (south in the sense of south of the latitude of Nigeria in territories in Central Africa). The remaining three species, those which occur in both reasonably dry and reasonably wet forest conditions in Nigeria and West Cameroun, extend both west and east and south of Nigeria and West Cameroun.Some type of thicket or forest vegetation is the essential habitat for the survival of all six species of the fusca group. The main areas inhabited by the fusca group now are forest reserves in Western Nigeria and the relatively undisturbed forests of West Cameroun. The species are absent from much of southern Nigeria, and it seems certain that the increase of the human population over relatively recent times, and the effects that this increased density of population has had on the flora and fauna, has been the cause of the present-day discontinuous distribution of the fusca group in southern Nigeria. Man has an adverse effect on fusca-group tsetse populations through clearing of forest vegetation and the hunting and driving away of the game animals on which the flies depend for food. An inverse relationship between human population density and the number of records of the fusca group over southern Nigeria and West Cameroun is demonstrated.