Tsetse flies

The tsetse fly (Glossina sp., pictured left) is found only in Africa and carries trypanosomes (the disease agents causing human sleeping sickness and animal trypanosomosis). The disease is a serious problem in Sub-Saharan Africa and it is estimated that the removal of this disease could double livestock production and markedly increase cultivation levels there. Trypanosomosis has recently been found in South America, where it is transmitted by biting insects other than the tsetse fly. These do not actually harbor the disease organism in their bodies, but carry infected blood from one animal to the other.

There are two basic ways to combat the disease: remove the tsetse fly vector, or treat the infected animal with drugs. Both methods have been extensively used, with varying degrees of success: drug resistance is becoming a problem in many areas, and few, if any new drugs are being developed; numerous techniques of tsetse control have been employed, most of which work in the short to medium term, but then the cleared areas are re-invaded unless control efforts are continuously maintained.

As a result, it has become more evident that tsetse control efforts must be tailored to the type of fly populations - isolated populations may possibly be eradicated once and for all, because the risk of reinvasion is relatively low, whereas large area populations may be progressively reduced along the edges of the distribution. It is therefore vital to know where the flies are before effective control measures can be deployed.

The tsetse fly is very sensitive to environmental conditions - it will not survive in areas that are too hot, too dry, or too high. There are, however, twenty three species, many of which have different habitats and different levels of susceptibility to climatic conditions. On the other hand, because satellite imagery can provide reliable measures

of climate and environment, we can use it to make quite detailed maps of the distributions of the various fly species, which are a significant improvement over the maps produced before the advent of the predictive techniques that we now have.

In 1999, FAO and DFID commissioned the mapping of all twenty three species using remotely sensed imagery, which you can see on its own tsetse map website. Some examples are included within this Atlas which you can view by clicking on the thumbnails:

The distribution of the three Species Groups: Morsitans (savanna species and include the most effective vector of sleeping sickness, Glossina morsitans); Fusca (forest loving species); and Palpalis (which inhabit riverine habitats).

The predicted increase in cattle densities that would follow the total removal of tsetse. It has been calculated by taking the predictive equations used to generate cattle densities and setting the number of tsetse species to zero. This provides the number of cattle with no tsetse from which we have subtracted the predicted number when tsetse are present, to give the calculated impact of tsetse removal. This map is a first effort at producing a tsetse impact map, and we realize that the assumptions are very simplistic. It is, however, an indication of what might happen if tsetse control was implemented, and we hope to be able to improve it in the reasonably near future. Impact maps such as this have been used as a first step in choosing areas (or targeting) where tsetse control might produce most benefit to farmers.