﻿68 DR. J. W. SCOTT MACFIE — EXPERIMENTS AND 



3. When shaded, exposure for one hour to a temperature of 40°-41° C. is fatal 



to the male G. palpalis. Higher temperatures are more rapidly fatal. 



4. The presence of water enables G. palpalis to withstand for a longer period the 



action of direct sunlight, and perhaps of a shade temperature of 40°-41° C. 

 It is probable, therefore, that the diminution in the number of tsetse-flies 

 during the dry season, and their limitation to the bush along the river banks, is 

 due not so much to the low temperatures registered at nights during this season, 

 nor to the high temperatures occurring during the days, as to the dryness of 

 the atmosphere and the burnt up condition of the country. 



Notes on the Bionomics of Glossina Palpalis. 



The following more or less disconnected observations and experiments were 

 made at Zungeru in Northern Nigeria during December, 1911, and January, 

 1912. These months cover the height of the dry season when the tsetse-flies 

 (G. palpalis) are restricted to a few shady patches of bush along the river banks, 

 probably owing (as indicated by the foregoing experiments) to their intolerance of 

 the dryness of the atmosphere and the burnt up condition of the country. Of the 

 flies brought to me the proportion of males to females was as three to one, but 

 whether this was due to the females being actually less numerous than the males, 

 or to the fact that they were shyer feeders or more cunning at avoiding capture, 

 it is impossible to say. The fact that in some of the temperature experiments 

 the females seemed to be more sensitive than the males to a raising of the tem- 

 perature may have had something to do with it, as they may have been less eager 

 to fly out into the sunshine to feed and may thus have escaped capture. The 

 converse, namely that the female is apparently less affected by cold, may account 

 for the fact that on one occasion only, on a singularly cool and sunless day, the 

 proportion was reversed, namely three females being taken for every male. 

 The flies were also found to be susceptible to wind, and on the days when the 

 harmattan wind was blowing strongly few or no flies were caught. 



Feeding and Digestion. 



In considering the processes of feeding and digestion of G. palpalis it was 

 found to be essential that the flies should be naturally fed. At first, attempts 

 were made to feed them on such things as the liver of a fowl just killed, or 

 even on freshly shed human blood, but although the flies sometimes succeeded in 

 sucking nourishment from them, they were not able to get a full normal feed, and 

 it was at once recognised that the digestion of such meals was abnormal. In a 

 few instances the flies were fed on dogs, cats and guinea-pigs, but even on such 

 animals the act of feeding did not seem to be quite natural, and often occupied as 

 long as five minutes, whereas on the human body the flies seldom remained longer 

 than one or two minutes, if undisturbed, before flying off fully distended with 

 blood. In the case of the guinea-pigs, the flies showed a curious reluctance to 

 feed even Avhen suffering so severely from starvation that they died a few hours 

 later. The flies were therefore allowed to feed on my own fingers in all the 

 experiments referred to below. 



