274 SCIENCE IN AFRICA 



that this laboratory research may point the way to promising Knes 

 of investigation later under field conditions, which may lead to 

 something practicable in the way of alternative measures of con- 

 trolling G. morsitans. 



In Nigeria the problem of tsetse research is rather different, 

 being at present connected more with trypanosomiasis of human 

 beings than of cattle. The medical aspects of the problem are 

 considered in Chapter XVI. A special Sleeping Sickness Service, 

 which includes entomological research, is maintained by the Medi- 

 cal Department. Dr. Lester is in charge of this, with offices at 

 Kaduna, the capital of the Northern Provinces, and a laboratory is 

 maintained at Gadau, with a medical officer and an entomologist. 

 Dr. T. A. M. Nash; a second entomologist has been appointed 

 from 1938. There are only three species of Glossina in Nigeria of 

 economic importance: namely G. morsitans, G. tachinoides and G. 

 palpalis. Of these G. morsitans is the least important because it 

 only occurs in very thinly populated areas where big game still 

 survives in large numbers. G. tachinoides and G. palpalis, on the 

 other hand, thrive in the densely populated areas where man and 

 reptiles form the primary food supply. Since big game is the 

 reservoir from which tsetse become infected with the trypanosomes 

 that affect domestic animals, it is mainly in the thinly populated 

 areas that the fly are highly infected — areas in which little damage 

 can be done. Probably the bulk of cattle trypanosomiasis origin- 

 ates when the Fulani drive herds of cattle along trade routes 

 through these big game areas. Owing, however, to the dense popu- 

 lation in most parts of Nigeria, which limits the areas where big 

 game is abundant, cattle trypanosomiasis presents less serious prob- 

 lems than elsewhere in Africa. 



In the Northern Provinces all three species concentrate in the 

 dense vegetation bordering streams and rivers, to which they are 

 driven by the intense heat and desiccating atmosphere of the open 

 country. Since the wet season in that country is very short, fly 

 cannot spread far away from the streams before the next dry 

 season drives them back to the riverine vegetation. The distribu- 

 tion of Glossina is thus linear, following the streams, and the inter- 

 vening country is fly-free. The enormous fly belts typical of Eastern 

 Africa do not occur, solely because the West African dry season is 



