396 MEDICAL ENTOMOLOGY 



surroundings. It can also be brought about by excessive moisture. Its 

 occurrence is an indication of the necessity for quiet and rest during this 

 stage, and is in agreement with what is found in nature, that flies nearly 

 ready to give birth to their larvae remain at rest in the deep shade, and 

 are seldom seen on the wing. Abortion produces no ill effects on the 

 parent. 



Intra-uterine nymphosis, which always results in the death of both 

 the fly and its offspring, may also occur in captive flies, and has been 

 once observed by Roubaud in nature. The larva is unable to escape 

 by its own efforts, even if the mother dies at the time when it is ready 

 to emerge. 



Gestation has a marked influence on the nutrition of the female. At 

 the commencement of pregnancy, and immediately after the birth of a 

 larva, the fly will feed readily and fill itself to its utmost capacity, but 

 as gestation proceeds and the abdominal cavity becomes more and more 

 distended food is partaken of less eagerly, until by the time the larva can 

 be seen through the abdominal wall the fly cannot be induced to feed 

 at all. 



Tnere is, perhaps, nothing more striking in the bionomics of Glossina 

 palpalis than its high degree of susceptibility to slight changes in the 



temperature and humidity of the atmosphere. It can 



Effects of temperature i j - rr i 



'd't y survive and carry on its life processes in a normal 



manner in such conditions as are provided by the river 

 banks and tropical forest glades which are its natural environment, and 

 in order to keep it in captivity the corresponding atmospheric conditions 

 must be realized. The closeness of its relations to its environment are 

 well brought out in some experiments recorded by Roubaud. He found 

 that at the ordinary temperature of his laboratory (26C.) the female fly 

 would feed only every third day, when the previous meal was entirely 

 digested, and that it could not be induced to bite on the second ; an 

 hour's exposure to a temperature of 28C., however, resulted in an 

 unusual activity, and the fly fed at once when a host was offered to it. 

 This is in agreement with the frequently made observation that the flies 

 in nature will only bite during warm and sunny weather. The stimulat- 

 ing effect of increased temperature is only brought about within narrow 

 limits, for if the flies are maintained at a temperature of 30C. to 35C. 

 they die in three or four days. Roubaud concludes that the optimum 

 temperature for nutrition appears to be about 28C., with a variation 

 from 26C. to 30C. Even if maintained at a temperature of 30C., 

 with an average humidity (70 per cent.), they will not survive. 



