TSETSE-FLIES AND COLONISATION 217 



which -is produced by the preceding species of trypanosome. 

 The vector is Glossina morsitans. 



Trypanosomiasis (nagana, etc.) in domestic stock is trans- 

 mitted by several species of Glossina. It is impossible to keep 

 stock in fly country, as the animals readily contract the disease 

 and soon die. 



The foregoing may be taken as a very brief summary of 

 that part of my lecture which dealt with the morphology and 

 bionomics of tsetse-flies. It is obvious, however, that these 

 insects form a serious barrier in the way of settlement and of 

 the opening up of new trade routes through fly-infested regions. 

 There is need, therefore, of preventive operations, or the prac- 

 tical application of the facts which have been gathered from 

 a careful and prolonged study of the diseases by many experts 

 in various parts of Africa. These may be briefly considered 

 under the following heads : 



1. Clearing. I attach greater importance to this method, 

 in localised areas, than to any other means which have been 

 devised or recommended. Although the clearing of forest 

 or scrub may not destroy the fly, one may safely say that the 

 removal of vegetation such as is undoubtedly necessary for 

 the existence of the fly would result in its complete banish- 

 ment from the area thus treated. This method has been 

 carried out in various parts of Africa, and there is abundant 

 evidence to prove that clearings made in belts of forest fre- 

 quented by Glossina palpalis have met with marked success. 

 We have evidence to prove, moreover, that G. morsitans does 

 not habitually occur in open spaces or in relatively open 

 country, and to this I can abundantly testify from my own 

 observations in Nyasaland. I maintain, therefore, that 

 persistent localised clearing should be rigorously enforced 

 throughout the whole of the fly-infested country, that is, in 

 the immediate neighbourhood of populated centres or settle- 

 ments and along the trade routes. 



2. Destruction of Flies in their Breeding-places. In view of 

 the discoveries which have been made by various ento- 

 mologists, the collecting of pupae, either by searching for them 



