THE TvSETSE PROBLEM IN NORTH MOSSURISE. 377 



were created such as could probably only be made a })ermanency with settlement 

 behind it. Whether the returning game would bring fly in again \vould depend on 

 ( 1 ) whether the w^hole continuous fly area had been cleared of fly, or (2) whether 

 the portion cleared had been split of! from the imcleared portion by an efEective 

 barrier against the fly itself. 



West of the Sitatongas the country is much more jungly, and wholesale game 

 destruction is proportionately more difficult. In addition this country abounds 

 in bush-pigs, which are difficult to destroy and which in anything approaching 

 their present numbers can probably alone support the fly, with baboons, abundant 

 cane-rats and other animals which may all contribute to its sustenance. I consider 

 that it wdll be impossible to starve the fly at all generally by ordinary game destruc- 

 tion here, at any rate before the country is very fully settled, though buffalos and 

 elephants might be banished by adequate and persistent shooting. 



What can be done is to protect particular places, like Spungabera and the British 

 border, that are outside the fly and are threatened only by the wanderings thence 

 of the bigger game. Fencing, the judicious placing of native kraals and shooting 

 are amongst the possible measures, and organised and repeated drives might be 

 undertaken locally. I have suggested similar means of keeping the fly from being 

 carried into any areas that may in the future be settled. 



Again (cf. p. 355) it seems to me that game destruction should check the advance 

 of a fly-belt, whatever its effects on the ground already infested. No problems 

 are at present better worthy of study than these — (1) the extent to which tsetses 

 will travel independently of game, and (2) the distances that the female will travel 

 on game. 



An Attack on the Concentrations. 



At first sight, the weak point of morsitans in the area in which I have seen it w^ould 

 appear to lie in its most striking attachment to the vicinity of more or less moist 

 spots and in the great numbers in which it breeds there. One is strongly tempted 

 thereby to suggest that for areas in which this is the rule further experimentation 

 should be carried out on these distributing, and probably receiving, centres ; 

 experiments in local clearing of varying widths, in planting vleis and their margins 

 with the heavy wooding avoided by iiwrsitans,'^ poisoning and gassing the male 

 clusters (torpid on dewy mornings) and the bush just immediately adjacent, catching 

 with the aid of cattle, pupa-destroymg or any other methods against either sex 

 or either stage how^ever remotely promising, suggest themselves as worthy of trial 

 before the idea of attacking nwrsitans at its concentrations is finally given up. 



The essential point to ascertain, however, supposing such measures to be capable 

 of exterminating the fly at the concentrations, is the value or otherwise of the 

 " stray" flies (which comprise both sexes) for the survival of the species, and whether 

 these would continue indefinitely to escape the measures applied at the centres — ■ 

 always supposing that, in the area concerned, they are not and cannot be driven in 



* To check radiation, introduce shade conditions inimical to the fly and spoil the game's 

 early gTazing, also if the trees that succeeded were of a definitely " drying " type, like 

 FAicalypts, to help to dry the ground. Such a measure, even if locaUy successful, would 

 doubtless be too expensive to use except under special circumstances. 



