THE TSETSE PROBLEM IN NORTH MOSSURISE. -j-J 1 



The mountain sets were sent up late in June and more than a month of very cold 

 weather supervened, including, it is stated, the coldest that we have had for some 

 years. Without going into the details here it may be said that the tsetses of the low 

 veld control showed no advantage over those of the highland experiments. The 

 percentage of failures was approximately the same, and the emergences both of the 

 tsetses and of their parasites took place as well in the mountains as below. Tliis 

 is perhaps not surprising when one considers the elevation at which morsitans 

 occurs in Mashonaland. 



I could only test brevipalpis observationally. On 27th-28th August, the colder 

 weather being just over, I climbed the hills overlooking the Inyamadzi towards 

 Spungabera up which the continuous Brachystegia bush extends to a considerable 

 elevation, and I found brevipalpis present on the highest points at which bush 

 conditions (except in certain inaccessible kloofs) were suitable for that fly — that 

 is, so far as I could judge from the known elevation of the valley bottom, at an 

 altitude of about 3,000 feet. It was steep and rugged here, but tracks of pigs and 

 baboons were present. I understand that Jack took a pallidipes in August 1917, 

 almost at the level of Spungabera, but the place (pointed out to me by 

 Dr. Lawrence) suggests that it was a " carried " fly stranded there. In these 

 observations on brevipalpis there was no break in the fly's continuity, and from 

 one to several flies attacked from the thickets right along from the Buzi to these 

 high points near the border and back. 



I have already referred to my observation at Makwiana's escarpment (fly at the 

 bottom but none at the top), but this was simply a matter of shade versus none. 

 The cattle sustained early morning attacks (before sunrise) from both brevipalpis 

 and pallidipes with the thermometer at 47° F. and under. G. austeni was taken at 

 an elevation of (probably) six or seven hundred feet. 



Shadeless Barriers. 



The isolation of patches of woodland suitable for the tsetse seemed of some 

 importance in relation to G. brevipalpis in Brachystegia bush on the extreme edge 

 of its area and where the intervening bush was already stripped of shade. 



Ascending at the end of August the slopes from the upper Buzi or Inyamadzi, 

 or merely passing along near the bottom of the valley of the latter river with no 

 alteration in elevation, one came out into completely leafless bush (Pterocarpus) 

 or open grass, and I failed to find any fly at all in kloof strips or Brachystegia groves 

 isolated in or by these shadeless stretches, although they were certainly too narrow 

 on the Inyamadzi to act as a definite barrier to either sex. 



The obvious explanation seemed to lie in the refusal of brevipalpis to venture 

 outside continuous shady bush except under certain conditions of light not common 

 in the dry season, and then probably only if it can find a non-human carrier to 

 take it. Unfortunately for this view and the practical suggestion arising from it, 

 throughout the parts traversed of the low-lying crescent (Umzila's guard-area) 

 that descends the Mtshanedzi and swings back up the Puizisi, the smallest patches 

 of dense forest with shrub growth below were very apt to shelter brevipalpis, few 

 or many. The fact that the intervening bush was not yet leafless (in August) 

 doubtless helped, and in places (as on the road east of the Chikambwe) this bush 



