ENTOMOLOGY 275 



SO severe that the woodland savannah cannot support the tsetse. 



The primary carriers of human trypanosomiasis are G. tachi- 

 noides in the Northern Provinces and G. palpalis in the Southern, 

 which can exist and thrive in thickly populated areas. There is 

 an intermediate zone where both species are of nearly equal impor- 

 tance. Up to 1 93 1 it was thought that sleeping sickness occurred 

 in definite belts throughout Nigeria, and that continued campaigns 

 for medical treatment would reduce it to control. It has since been 

 found, however, that sleeping sickness is not limited to fixed belts, 

 and that the proportion of infected people in certain provinces, 

 notably Zaria, where over a quarter of a million people have been 

 examined and 20 per cent, were found to have sleeping sickness, 

 is far too high to be controlled except by a very large organization. 

 There is evidence, moreover, that the incidence of the disease has 

 increased considerably in Nigeria under British occupation, since, 

 under its greater security, the people have left their large villages 

 and have scattered into small bush-hamlets, thereby coming into 

 more frequent contact with the fly. Accordingly the Colonial 

 Development Fund has accepted an application for assistance in 

 a large sleeping sickness and tsetse campaign, to include an exten- 

 sion of the present research organization. 



It is clear that protective measures, aiming at reducing the man- 

 fly contact, give the most hopeful lines of attack. The eradication 

 of fly from native villages by clearing the banks of streams is an 

 essential measure. Some provision for this has been made in the 

 new Sleeping Sickness Ordinance (Nigeria 1937), partly based on 

 the Uganda Ordinance, which has been acted on for many years. 



The choice of methods to be employed against the fly depends, 

 of course, on the results of research into the ecology of the flies. 

 The original researches at Gadau, carried out by Drs. Lloyd and 

 Johnson (now Sir Walter Johnson) (1923), provided a general 

 survey of the problem in Northern Nigeria. The work of Nash 

 ( 1 93^5 33? 34? 35? 37) during the past few years is of special interest 

 in relation to control measures. His studies of the climates in the 

 environment of the flies, both in the field and laboratory, show that 

 the maximum shade temperature which G. morsitans and G. tachi- 

 noides can withstand is io6°F., and since this temperature is often 

 exceeded in the woodland in the drier parts of Nigeria, the fly 



