376 C. F. M. SWYNNERTON. 



These will be inferred sufficiently from what I have said in this report, but I will add 

 here that in the piece of country in question, along the streams and rivers and in 

 larger blocks on the Lusitu, first-class timber trees — mahogany (Khaya), musando, 

 mowana {Adina) and others— are present in quite unusual numbers. These, floated 

 down the Lusitu, might in some cases help much to defray the cost of clearing. 



Secondly, no ingress of large game must be allowed from areas still under fly. 

 The best barrier — with the elephants away— might be a strong, patrolled fence ; 

 but if the fringes of the area are sufficiently closely settled it is likely, even from our 

 present imperfect success on the lightly settled border, that this fact alone, with 

 shooting, will suffice to keep off the elephants, buffalos and elands. It is these three 

 animals that pro])ably chiefly matter. 



Umzila's principle — the settling and clearmg of the low-lying guard-area only, the 

 enclosed hill mass then taking care of itself and being perhaps disposed of later at an 

 enhanced value — would be well worth consideration and investigation. Under such 

 a scheme, carried out with thoroughness, it seems at present fairly certain that cattle 

 could, after a few years, be kept safely and in numbers on the dolerite. 



If, on the other hand, the settlement should have to be a gradual gro"\Ai;h from 

 small beginnings, its safest base would be the deciduous part of the British border, 

 a block at a time being settled and special measures being taken against the buffaloB. 



The settlement of the two permanent fly-areas themselves would mean the end of the 

 menace. The great strip on the Lusitu that is now occupied by rubber forest, both 

 east and west of the river's southward turn, represents some of the finesb agricultural 

 ground in the country and is in immediate touch with the Lusitu- Buzi waterway. 

 Much clearing is necessary, but the farms here could be small. The " Oblong " 

 offers greater difficulty. The soils on the whole are distinctly useful, though less 

 rich than in the other brevipalpis-avea, but there is relatively little permanently 

 running water away from the big rivers. Pools, however, persist in most cases and 

 water should be obtained in this formation at no great depths by boring and sinking. 



« 

 XXI. — ^Discussion of General Methods of Tsetse Control. 



Game Destruction. 



In view of the evidence I have already aUuded to (p. 336 and elsewhere) we are 

 bound to keep an open mind with regard to the possibilit}^ that even G. morsitans 

 might survive the destruction of all large mammalian life. Yet the fact that under 

 present conditions game-paths are the regular rendezvous of the sexes, and that 

 the connection with game appears generally to be an essential point in their rather 

 complicated social scheme, makes one hesitate to reject the alternative view. 

 Lamborn (Bull. Ent. Ees. vii, 1916, p. 37) has argued well for the view that it need not 

 be a large game population that will support fly, and this might be a sufficient 

 explanation of Umzila's continued trouble in the rubber forests. 



In a relatively clean-stenamed area like that on the granite-gneiss, in which also 

 bush-pigs are not over-abundant, it is to me very conceivable that wholesale game 

 destruction might banish the fly. An obstacle, however, would be that the whole 

 territory is one vast game area, so that the game would pour again into a given 

 section of it as soon as the persecution was relaxed — unless an effective barrier 



