THE TSETSE PROBLEM IN NORTH MOSSl^RISE. 37.'i 



18 years ago were relatively bare are now very fully wooded and capable of giriiig 

 a temporary support to tsetse. 



Up to a very few years ago cattle ivere still kept successfully in Mossurise within 

 a few miles of the British border from the Puizisi to Maruma, and from Spungabera 

 to the Inyamgamba. These, except the Spungabera cattle, which have suffered, 

 have been largely wiped out by successive attacks of nagana, especially during 

 the last three years. At the same time isolated outbreaks, here and therv?, have 

 taken place on farms just on the British side of the border. In a remarkable pro- 

 portion of cases a connection has appeared to exist between the outbreak and the 

 wanderings of buffalo. 



The incursions of buffalo into the cattle-carrying areas have undoubtedly increased 

 greatly in the years concerned. The northern outbreaks coincided with or followed 

 the invasion of Mafusi's country by considerable numbers of buffalos from the 

 Bouth and their coming in contact with the brevipalpis-pallidipes area there. 

 In the section opposite Spungabera (across the Buzi) these animals are certainly 

 far more in evidence, and in far larger numbers, than they were some years ago, 

 as I know from shooting trips on the Upper Mtshanedzi in 1901 and 1902. 



Elands have also greatly increased, as have pigs ; and it ls likely enough that 

 the fly itself has increased within its permanent haunts in consequence of the great 

 and progressive increase in its food, and of the earlier burning of the grass. This 

 would contribute to the menace, and it is by no means incompatible with the fact, 

 of which I am convinced, that such destruction of the big game as might be easily 

 feasible would not alter the fly's permanent boundaries, though it would certainly 

 prevent it from being carried into contact with the cattle. 



The great increase in the wandering game has undoubtedly been the main factor 

 in the outbreaks of the past few years. But it may be said that it is especially 

 hard to distinguish the separate original infections where natives' cattle are con- 

 cerned, owing to the likelihood of infection by mechanical transmission by other 

 biting flies that is incurred through their placing the survivors in the herds of 

 their neighbours, and by their movements of cattle in connection with thoir 

 matrimonial affairs. 



XIX. — Clearing Experiments. 



These were carried out only to ascertain the effect on the fly of the clearing of 

 undergrowth (PL xvi). 



Experiment 1 . To ascertain the effect of clearing tlie undergrouith in primary forest. 

 The whole width of the dense undergrowth of the Inyamarimu forest strip w^as cleart^d 

 to a length of 80 yards. The width varied from 40 to 70 yards. It was incidentally 

 open to penetration and passage from the sides by any flies there might be in the 

 Brachystegia-U apaca bush on either side of it. At 11.30 on the following day the 

 two oxen were driven into the middle of the clearing. They carried in with them 

 one fly, a male brevipalpis picked up in passing near some of the uncleared bush, 

 and this was at once removed. They were stood in the centre of the clearing and 

 from time to time moved across it a little though not to its edges. They had been 

 placed many times before in this spot and had never failed to be attacked by large 

 numbers of brevipalpis. This time in three hours only four came to them. 



