干旱区生态环境知识资源中心

Riverine tsetse, which are vectors of human and animal vectors, are very difficult to control because of the specific nature of their habitat and behaviour. The problem, however, is not technical, because nowadays entomologists have at their disposal a wide range of efficient methods to eradicate them. The problem is therefore practical, and it is related to the way in which these methods are used.

In fact, the entomologist is faced with several intractable problems that reduce his scope of action. First of all, because he has to pay due regard to the environment, he is obliged to refrain from taking any action that may be fatal for the tsetse, but harmful for the environment such as cutting down woody, scrub and shrub vegetation, setting bush fires, etc. Furthermore, he is not allowed to tamper with wildlife which is the nutritional source of the tsetse, but is also an important source of foreign exchange through tourism. He also must respect the non-target fauna, especially the aquatic fauna, with the result that this limits: (1) the choice of pesticides that can be used in one way or the other, affecting the chain in the biological cycle, invertebrates, fish, birds, mammals and (2) the method of application of chemical, because he cannot use residual sprays or aerial aerosols everywhere.

The entomologist must also take into account economic considerations. The world economic crisis has considerably reduced the availability of potential sources of donor funds, and most African countries afflicted by sleeping sickness and animal trypanosomiasis cannot individually undertake large-scale eradication campaigns for lack of funds, adequate equipment and trained manpower. Using aeroplanes or hordes of workers is therefore out of question. Similarly, controlling the tsetse through the use of sterile male release technique, which is a complementary control method to attain the 0 density, seems now to be unachievable because of the huge investments that are required.

Finally, many scientists, economists and ecologists have recently begun to wonder if controlling the tsetse is after all a good solution, since their disappearance would lead to the overexploitation of the land freed, resulting in the destruction of the vegetation and bio-climatic changes and finally total desertification. The challenge therefore is how to control the tsetse under these conditions.

The use of traps seems to be a good solution. Experiments conducted in Africa (and since the discovery of certain olfactive attractants) have shown that it is effective, safe for the environment, easy to use, and especially very cheap, when it is used by the rural communities. But even with trapping, a number of questions are being asked: Is it better to kill the tsetse than to sterilize it? Is impregnating it with an insecticide indispensable? Is there no risk of selecting a "trap resistant strain" of tsetse? Can the use of traps lead to eradication?

In fact, in most cases, eradication is wishful thinking and controlling the fly is the only realistic thing to do; the entomologist has to control, but cheaply and with a less harmful technique. Besides, because of its numerous qualities, trapping is the only method that can be used nowadays as long as it is used wisely.