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to the biology of Tsetse-flies : fly-zones or fly-belts, range of flight, 

 proportion of the sexes, seasonal variations, migrations, distribution of 

 breeding-places, etc. 



Clearing is at present chiefly carried out in Tropical Africa as a 

 means of protecting European settlements, native villages, cultivated 

 areas, wells and springs, landing places, fords, etc., against Glossina 

 palpalis, the principal disseminator of sleeping sickness. 



The work of clearing as a means of fighting G. palpalis belongs 

 especially to the domain of tropical medicine and hygiene, but what is 

 of service in the case of the species mentioned may likewise be applied 

 to Glossina morsitans, the Tsetse-fly of stock, the distribution of which 

 is much more extensive. 



" Since these Diptera are larviparous," writes Prof. E. Trouessart, 

 of the Paris Museum, "it is impossible for us to attack the larvae 

 themselves, and therefore in the vicinity of settlements we must 

 systematically destroy the bush, which serves as shelter for the flies 

 and provides them with spots in which to deposit their larvae. What 

 has to be done is thoroughly to clear woods and thickets of all under- 

 growth and scrub to a certain distance from farms, stables and stock- 

 pens. Bush bordering roads, or surrounding or intersecting grazing- 

 grounds, must likewise be grubbed up and destroyed ; it is also 

 necessary to clear away scrub and tall grass for a considerable distance 

 round watering-places, while the low vegetation growing under the 

 shelter of bushes should be torn up and burned. If cattle remain in 

 the open all night, it is well to surround them with fires producing an 

 abundance of smoke, in order to keep away insects. Should it be 

 necessary to make enclosures, instead of employing growing hedges it 

 is always advisable to use simple fencing, or interlaced branches 

 stripped of foliage, which might afford shelter to Tsetse-flies. Lastly, 

 in the case of a locality free from Nagana, the utmost precautions 

 should be taken against introducing animals coming from a district in 

 which the disease is rife." 



With regard to G. palpalis in Uganda, Fiske (54), after prolonged 

 study of the bionomics of this species on the islands and shores of Lake 

 Victoria, expresses his conviction that : " It is wholly impractical to 

 consider any control measures involving artificial destruction of flies, 

 and wholly 'necessary to rely upon measures designed to deprive the 

 insects of either food or protection or to render food less available 

 to them." For various reasons, however, this author considers it 

 " inadvisable and even dangerous to contemplate control of the pest 

 through depriving it of food. It is probable," he continues, " that if 

 completely deprived of all favoured hosts it would be unable to exist 

 on hosts favoured to a no greater degree than sheep, goats and man, 

 but it is probable that it would continue to exist if cattle or pigs were 

 provided. It is also certain that where favoured hosts are plentiful, 

 man is almost immune to attack, but that when they are few man 

 is freely attacked, and our object must always be to protect man rather 

 than to destroy flies. 



" There is no such objection to the proposition of controlling fly 

 through depriving it of protection, and it is on measures designed to 

 this end that we must chiefly rely. They are the clearing measures 

 already in use, and they have been proved efficacious on many occasions. 

 The maximum of economy and efficiency is to be gained through clearing 

 at precisely the right points i.e., at the centres of infestation where 

 natural increase of fly is most rapid. By clearing these the dispersion 

 of flies into the surrounding zone is prevented, and the effect is general. 



