CONTROL OF TSETSE FLIES 501 



shade, in bush mixed with creepers and young trees near water 

 courses. Its counterpart in the more northern parts of East 

 Africa is Glossina longipennis, a lai'ge warm-brown species with 

 indistinct markings. G. brevipalpis is said to be desirous of 

 feeding only before 8.00 a.m. and after 4.00 p.m. In the middle 

 of the day it hides urider leaves or grass blades near the ground, 

 so that its presence would never be suspected. 



To sum up it may be said that while there is much variation 

 in the susceptibility of different species of tsetses to different 

 trypanosome infections, so that one or a few species come to 

 serve as the usual transmitters of any particular trypanosome, 

 yet other species cannot be definitely excluded as carriers with- 

 out extended experimentation. Even in the case of natural 

 carriers of a particular trypanosome, a very small per cent of 

 flies are found naturally infected, and not more than a few per 

 cent can be infected experimentally. Moreover it is evident 

 that a single species of fly shows marked differences in recep- 

 tivity to infection in different parts of the range. The re- 

 fractory nature of some West African races of G. palpalis prob- 

 ably accounts for the absence of sleeping sickness in Dahomey 

 and neighboring states. It is probable that climatic conditions 

 and food habits play a leading part in determining susceptibility 

 of flies to trypanosome infections. 



ControL — Attacks of tsetse flies can be avoided to some ex- 

 tent by the use of the usual insect repellents (see p. 455), by 

 fly-proof clothing or veils, and by wearing white clothes. When 

 it is necessary to travel through fly-infested places where sleeping 

 sickness occurs, all of such measures should be adopted, or, 

 better still, the fly-belts should be passed through in the dark- 

 ness of night when the insects are inactive. Railroad trains and 

 steamboats passing through fly-belts should be protected by 

 fly-proof screens; this expedient is adopted in many parts of 

 Africa at the present time. 



Extermination of tsetses on a large scale is a very difficult 

 matter, but locafly it is quite feasible. There are probably 

 factors' influencing the distribution of the flies which are still 

 unknown, and which may be turned to account in destroying 



them. 



Clearing away of brush along fly-infested streams m the case 

 of such species as G. palpalis and G. tachinoides, which are closely 



