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



No. 4. — Male G. palpalis. 

 8.50 p.m T. 10° C. Fly introduced into the cold chamber. He buzzed 



about for a moment, alighted on the side of the jar, 

 and fell over immediately " as if dead." 



8.52 



T. 



8 



8.55 



T. 



4 



9.0 



T. 



3 



9.5 



T. 



2*5 



9.10 



T. 



3 



9.15 



T. 



3 



9.20 



T. 



3-5 



9.25 



T. 



4 



9.28 







9.31 







9.40 







10.0 







Fly removed from the cold chamber having been in 



an inert condition for 35 minutes. 

 Temperature of the external air — 26° C. 

 Slight movements of the legs. 

 Abortive attempts at flight. 

 Still very unsteady on his feet. 

 Able to fly, but still very uncertain on his feet. 

 This fly never recovered completely, but died at about 9.30 a.m. on the 

 following morning. 



The immediate effect of a lowering of the temperature on G. palpalis is to 

 cause a reduction in activity. Should the temperature fall to a point varying* 

 from 10° C. to 6' 5° C. the fly becomes inert, and falls to the ground as if dead. 

 Partial recovery was found to occur even after half an hour's exposure in this 

 condition to a temperature ranging from 2*5° C. to 4° C. Recovery from less 

 severe exposures was complete, and accompanied by violent buzzing. 



In Zungeru, as will be seen on reference to the meteorological return for 1910, 

 given above, such low temperatures as those used in these experiments do not 

 occur. The same applies in the case of the other stations in Northern Nigeria 

 in which G. palpalis is found. Practically never does the temperature fall as low 

 as 10° C, a degree of cold which G. palpalis has been shown experimentally to 

 withstand for a considerable length of time. No doubt, however, the cold of 

 the harmattan does play a part in the reduction of the number of tsetse-flies 

 during the dry season, by numbing them so that they cannot feed, and by 

 rendering them a more ready prey to their natural enemies. 



The Effect of Raising the Temperature. 



In considering the effect of a rise in temperature upon G. palpalis account 

 must be taken of the highest temperatures to which the fly may naturally be 

 exposed. On reference to the meteorological return for Zungeru, given above* 

 it will be seen that these occur during the months covering the latter part of the 

 dry season and the commencement of the rainy season, and that the maximum 

 temperature recorded in 1910 was 107° F. (or 41*6 C). High temperatures, 

 therefore, occur both when the degree of humidity of the atmosphere is low, and 

 when it is beginning to rise owing to the onset of the rains ; and account of this 

 had to be taken in planning experiments. It was also recognised at the outset 



