490 OTHER BU)OD-vSUCKING FLIES 



iiioiv or less like a small olive, aiul has at the tip of the body the 

 blackish knohs 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 daj'S to nearly 

 three months. In experiments made by Lloyd with Glossina 

 7norsitnns the pupal stage ranged from 23 days at 85° ¥. 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 onh- 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. mor.sitaiis 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. Speeiniens have been kept in the laboratory for o\-er eight 

 months. 



Tsetse Flies and Disease. — As remarkt-d i)efore, 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 thesQ aids to development and 

 civilization from some parts of that continent. The importance 

 of trypanosomes to man in .\frica is discussed in riiaj). M. 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 ino.st deadly, disease known. Several types of the disease 

 are recognized; the most widespread (lambian disease is caused 

 by Tri/panosomn (jambiense and in nature is transmitted chicHy 

 if not exclusi\-ely by Glossina piilixilis. The mild Nigerian form 

 of the di.sease is believed to he a mere varietv of the (lambian 



