NOTES ON THE BIONOMICS OF GLOSSINA MORSITANS. 1 2:> 



Is it not possible that this hinitation might account to some extent for the gre- 

 garious habit of the tsetse, the flies benefiting by the combined perceptive powers 

 of a number instead of relying on those of single individuals ? The value of numbers 

 in regard to perception will hardly need urging upon anyone who has hunted antelope 

 or other gregarious game. 



The Following Distance of Female Flies. 



It appears very important that attempts should be made to determine as accurately 

 as possible the maximum distance to which female flies may be carried by game, 

 man, etc. The point has a great bearing upon the question as to w^hat would con- 

 stitute an effective barrier to the fly's advance, and also upon the question of the fly 

 as a whole migrating with game or moving about the fly area in company with its 

 hosts. The writer. has as yet been able to prove following on the part of the females 

 up to only about 400 yards, although one instance has occurred where a specimen 

 had ajpj)arently followed very much further than this, over a mile in fact. The ob- 

 servation in the latter case was, however, hable to considerable error. Some 

 experiments in this connection were planned for the writer's visit to Sipane Vlei in 

 August 1919, but could not be carried out owing to the unexpected scarcity of fly in 

 that centre. 



Sipane Vlei and some other Localities in 1919. 



In a recent paper * the writer pointed out that the somewhat delicately balanced 

 state of aflairs which exists at the most favourable dry season haunts of the tsetse, 

 namely the margin of vleis containing green grass in the dry season, is apparently 

 hable to be somew^hat easily disturbed by any agency tending to prevent game from 

 visiting the vlei with its normal regularity. This disturbance, it was pointed out, 

 would enhance the effect of game reduction by hunters, and might also have operated 

 in the rinderpest epizootic, which undoubtedly induced abnormal movements of the 

 panic-stricken remnants. These views have received some indirect support during 

 the dry season of 1919, when for the first time since the rinderpest a reduction of fly 

 in areas of the territory unaflected by civihsation has been recorded. This reduction 

 is local, and extension since the previous year was recorded in one other part of the 

 €ountry, and may have occurred elsewhere. A reduction has been reported 

 in the northern part of the Umniati fly area by Dr. Alec Mackenzie of Gatooma. 

 Dr. Mackenzie's statement is to the effect that he found no fly at all in December 1919 

 in many parts where they are usually numerous near the Sakugwe and Umniati 

 Kivers on the road from Gatooma to the Emerald Mine, and only a few finally at the 

 headwaters of the Mvumvudzi and Urungwe Rivers, visited for the express purpose 

 of locating the fly. There is, however, one spot where reduction can be proved on 

 something like a mathematical basis, namely Sipane Vlei, lying between the Sengwa 

 and Sassame Rivers in the Sebungwe district. 



The rapidly-expanding Sebungwe fly area reached the Sengwa River from the west 

 by 1910, and fly was first recorded at Sipane in 1913, though it may have been present 

 at least a year earher. In late September of that year it was present in great numbers, 

 and 87 were caught with a net in one hour, in order to estabhsh some sort of basis for 



*Bull. Ent. Kes. x, p. 83. 



