496 OTHER BLOOD-SUCKING FLIES 



more or less like a small olive, and has at the tip of the body the 

 blackish knobs which are so characteristic of the larval stage also. 

 The shape and size of the knobs and of the notch between them 

 are good distinguishing marks between species. The duration 

 of the pupal stage depends on the dryness of the soil, temperature, 

 exposure to sunlight, etc., and may occupy from 17 days to nearly 

 three months. In experiments made by Lloyd with Glossina 

 morsitans the pupal stage ranged from 23 days at 85 F. to 81 days 

 at 70. Few adults emerged at temperatures below 70 or above 

 86. Little is known about the reproductive season, but it is 

 probable that reproduction occurs only in the warm part of the 

 dry season in cool climates, but may occur to a varying degree 

 throughout the year in hot climates. 



The places selected for depositing the eggs vary somewhat 

 with the species, but all species select dry, loose soil in shaded, 

 protected spots, preferably in places where a little sunlight will 

 penetrate for a short time each day and where scratching birds 

 cannot easily reach them. G. palpalis deposits under tree trunks 

 and at the foot of various species of trees, especially where a 

 dense thicket gives a protected spot. In Sierra Leone, Yorke 

 and Blacklock found numerous pupal cases at the foot of oil- 

 palms where the dense foliage of the lower limbs makes approach 

 difficult. G. morsitans is partial to cavities in trees or stumps, 

 or under logs or branches lying a few inches above the ground 

 (Fig. 235). The length of life of tsetses is probably less than a 

 year. Specimens have been kept in the laboratory for over eight 

 months. 



Tsetse Flies and Disease. As remarked before, the enormous 

 importance of tsetse flies lies in their role as carriers of trypano- 

 somes. The effect of trypanosome diseases on domestic animals 

 in Africa has practically excluded these aids to development and 

 civilization from some parts of that continent. The importance 

 of trypanosomes to man in Africa is discussed in Chap. VI. It 

 is sufficient here to repeat that sleeping sickness, which is the 

 final stage of trypanosome disease, is one of the most deadly, if 

 not the most deadly, disease known. Several types of the disease 

 are recognized; the most widespread Gambian disease is caused 

 by Trypanosoma gambiense and in nature is transmitted chiefly 

 if not exclusively by Glossina palpalis. The mild Nigerian form 

 of the disease is believed to be a mere variety of the Gambian 



