BIONOMICS OP TSETSE, ETC., IN THE GOLD COAST. 195 



I. Factors Influencing the Distribution and Prevalence of Tsetse. 



Dr. Shircore* has drawn attention to what he calls " primary centres " in which 

 he says that Glossina morsitans segregate at the period when the conditions of life are 

 unfavourable elsewhere, and from which they disperse when water becomes abundant 

 and the country is covered with grass and the trees with foliage. Several writers 

 on this question in West Africa also refer to ' ' fly-belts. ' ' This term has been so loosely 

 used that it is sometimes difficult to establish what is actually meant. If by a " fly- 

 belt " is meant that at certain parts on a road tsetse are more abundant than else- 

 where, then such a state of affairs actually exists, but if by the term it is meant to 

 indicate that at certain parts these flies exist in numbers and are not to be found 

 elsewhere in the surrounding country, then the term is misleading and not in 

 accordance with the facts. In all my experience in West Africa I am not conscious 

 of any definite locality, either in the wet or dry season, containing tsetse actually cut 

 off from the surrounding country. To a casual observer this might appear to be so, 

 but if the intermediate country be thoroughly examined, it will be found that tsetse 

 exist linking up these so-called belts, though undoubtedly in smaller numbers. 



At the end of the dry season (December, January and February in West Africa), 

 when the forest fires are raging, tsetse (along with game) are undoubtedly driven 

 before them and take refuge in the denser bush unattacked by such fires, but the pupae 

 are seldom damaged and soon repopulate the area burnt, in addition to the adults 

 which return after a very short time. Thus, if an area over which an extensive bush 

 fire has been raging be examined immediately after the fire, no tsetse will be 

 encountered, but if the same area be examined a month later, tsetse will again be 

 found. This is a condition of a purely artificial character, and has no definite relation 

 to the natural segregation of the flies. 



In the Northern Territories of the Gold Coast at any rate, it is no doubt the case 

 that there is hardly a square mile where tsetse cannot be captured at some period of 

 the year. This is extremely important in the case of horse transport. In these 

 Territories certain areas are " proclaimed " for horses, but this precaution only leads 

 to a false security. There is no road between any two stations in the Northern 

 Territories free from tsetse, and as it is not the actual number of the flies, but the 

 proportion infected that counts, such a regulation is worse than useless. 



Type of Vegetation. — I have already in my reports on the different colonies in West 

 Africa given the types of vegetation associated with the various species of tsetse found 

 there, so need not reiterate these observations here. Briefly summarised, these might 

 be given as follows : — G. palpalis is found along the banks of rivers where vegetation 

 is dense, in " kurimis " (dense bush with abundant shade), and along the banks of 

 the smaller tributaries. G. tackinoides is an up-country form allied to G. palpalis, 

 and is found in similar localities on the higher reaches of the rivers. G. submorsitans 

 is seldom found near rivers and is more abundant in the savannah forest and open 

 savannah country ; I have found the species at least three miles from the nearest 

 water. In very open country where small water-holes exist, G. submorsitans is more 

 frequent, but this may be, and probably is, because game comes to water there. 

 G. submorsitans will, however, follow a herd of game a long distance, and undoubtedly 

 migrates in this manner. 



* Bull. Ent. Res., v, p. 87 

 (C419) a2 



