Distribution and Abundance of Tsetse Flies (Glossina Spp.)

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Abstract
(1) Two approaches are used to understand the distribution of tsetse. In the first, empirical, approach the distribution of Glossina palpalis and G. fuscipes in West and Central Africa is superimposed on a map showing ''contours'' of average annual temperature and saturation deficit. The northern distributional limits of both species correspond best with the joint condition that temperature and saturation deficit do not exceed 27.degree. C and 14 mm Hg respectively, while the southern, cooler, limit is set by the line of 6/7 mmHg saturation deficit. (2) In the second, analytical, approach mortality rates calculated from fly-round cathces of G. morsitans, G. palpalis and G. tachinoides have been related to the local climograms for the fly-round sites. A reproductive plane added to these mortality clomigrams allows the identification of both the bioclimatic limits (where reproduction just balances mortality) and the bioclimatic optimum (where reproduction exceeds mortality by the greatest amount) for each species. (3) The above three species show very different responses to a similar range of climatic conditions, which explains their differential distribution and may also account for the ability of G. palpalis and G. tachinoides to coexist, despite competition, in West Africa. (4) The abundance of flies, and the risk of disease transmission, may be greatest at the bioclimatic optimum for each species. Several areas of Africa with known current problems of trypanosomiasis correspond well with the bioclimatic optimum for G. morsitans. (5) Field data on the abundance of G. palpalis and G. tachinoides in northern Ivory Coast are compared with the predictions based on the mortality climograms for these species. The low availability of hosts in (forest) regions corresponding to the bioclimatic optimum of G. palpalis appears to have a significant impact on the abundance of this species. (6) The future use of the relationships established between tsetse distribution and abundance and climate in forecasting the changing risks of trypanosome transmission is discussed.