103 



by heat, and cannot therefore remain long exposed to the direct rays 

 of the sun. Tsetse-flies after being caught, if carried in pill-boxes with 

 other insects, are almost invariably the first to succumb to the effects 

 of heat ; the only method of keeping such flies alive consists in boring 

 air-holes in the lid of the box and keeping the latter in a cool place. 



A series of very interesting experiments upon the influence of 

 external factors cold, heat and moisture on Glossina palpalis was 

 made in 1910 at Zungeru, Northern Nigeria, by Dr. J. W. Scott Macfie,. 

 West African Medical Service (93). 



THE EFFECT OF A LOWERING OF THE TEMPERATURE. " In order to 

 determine the effect of lowering the temperature on G. palpalis/' 

 writes Dr. Macfie, " a simple cold chamber was constructed by filling 

 a large glass jar with ice and salt, or ice and water, in which a smaller 

 glass jar fitted with a thermometer was completely immersed. Into 

 the smaller jar the fly was introduced, together with some leafy twigs 

 on which it might alight. In such a chamber it was possible to watch 

 simultaneously the fluctuations of the temperature and the behaviour 

 of the imprisoned fly." 



By this means it was found that the female G. palpalis is " able to 

 withstand exposure for an hour and twenty minutes to a temperature 

 ranging from 10-7 C. (50-44 5 F.) without harm." "This is a 

 degree of cold to which -she would never be exposed naturally at 

 Zungeru, where the minimum temperature recorded in 1910 was 

 13-8 C." 



" 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 2-5C. to 4 C. Recovery from less severe exposures 

 was complete, and accompanied by violent buzzing." 



THE EFFECT OF RAISING THE TEMPERATURE. " In considering the 

 effect of a rise in temperature upon G. palpalis/' says Dr. Macfie, 

 " account must be taken of the highest temperatures to which the fly 

 may naturally be exposed ... It was also recognised at the 

 outset that a distinction must be made between shade temperatures, 

 and those attained by direct exposure to sunshine." 



In the experiments performed by Dr. Macfie, " tsetse-flies were 

 exposed to the various temperatures in glass jars fitted with a thermo- 

 meter. Twigs on which the flies might settle were always present. It 

 may be stated at once that the flies appeared to be much more sus- 

 ceptible to a raising of the temperature than they were found to be to 

 a lowering." In one of the previous experiments " the fly withstood 

 for some time a lowering of the temperature of 23-5C. (viz. from 

 26 C. to 2-5 C.), whereas in experiment No. 8 a raising of the tem- 

 perature only 10 C. (viz. from 34 C., the temperature of the external 

 air at the time of the experiment, to 43-44 C.) was more than could 

 be endured." 



^ Six experiments in all were made. In the first two the insects 

 " were exposed in glass jars to the direct rays of the sun. Small twigs 

 were included in the jars, but no water." As to the remaining tests, 

 Dr. Macfie writes : " The jars containing the flies in these experiments 

 were protected from the direct rays of the sun by a covering of thick 



