GLOSSINA INVESTIGATIONS IN NYASALAND. 



261 



The second series of experiments given in detail in the table below, was carried 

 out at Monkey Bay and consisted in liberating marked flies at the outskirts of bush 

 country favoured by tsetses and then recapturing as many as possible at definite 

 distances along a native path, which, like all these paths, was very devious, winding 

 in and out among thorn bushes. 



In connection with the whole question it is noteworthy that motor cyclists coming 

 into Fort Johnston commonly assert that the flies, which are abundant some thirty 

 miles to the south along the Zomba road, settle on their backs and are so brought 

 into the Fort. Residents confirm the statement, and it is therefore possible that 

 the large increase of motor traffic, which has taken place as a result of military 

 measures in the countr}^, may be indirectly responsible for the high mortality of the 

 cattle from trypanosomiasis which has occurred during the past few months at 

 the Fort, and may account for the occasional discovery of a stray tsetse in the 

 houses there. 



Date. 



No. of males 

 released. 



No. recaptiu-ed. 



Distance traversed. 



12.iv.l5 

 13.iv.l5 

 17.iv.l5 

 18.iv.l5 

 22.iv.15 

 23.iv.15 



100 

 100 

 100 

 100 

 100 

 100 



13 

 16 

 3 

 20 

 12 

 19 



^ mile. 



1 „ 



1| miles. 



H „ 



I have made a third series of flight experiments in the proclaimed area, releasing 

 marked male flies, as before, at a spot two miles south of the Lipimbi river, at an 

 altitude of 1,950 feet, and recapturing as many as possible in the region from which 

 they had been removed, namely Lingadzi, about five miles distant in direct line, 

 with an altitude of 1,700 feet. The country which they had necessarily traversed 

 in their return consists of thin woodland composed of thorn and other low trees 

 growing in rocky arid ground, in which area flies have from time to time been found, 

 though never in any great numbers, the region to which they returned being 

 characterised by the greater fertility of the soil, which is far less rocky and sandy, 

 by the greater luxuriance of a similar type of vegetation, and by the presence of a 

 greater amount of surface water, as a result of which game is much more abundant. 



In making these experiments every precaution was taken to guard against 

 possible fallacy. The flies were liberated by placing the cage in a tuft of grass before 

 opening the door, by which means it is possible for the person conducting the 

 experiment to get away to a distance before any flies are able to follow. In no case 

 did the person releasing them return to the tsetse area, and there was very little 

 probability of any flies returning on the backs of chance passers-by. 



