2U4 Journal or the Depaktment of Agiuculture. — Sept., 1922. 



Glossina pallidipes. — In order that this species may reproduce 

 its kind successfully, it requires to have a densely shaded breeding 

 ground and close by a regularly available food supply. In the later 

 stages of gestation the gravid females, still requiring food, must 

 have suitable shelter wherein to rest between meals and whereunder 

 the soil conditions are also suited to the requirements of their off- 

 spring. It appears that the females of this species cannot exist and 

 propagate unless these conditions occui', and the spot is visited practi- 

 cally every day by game. These shaded spots are relatively small 

 and overhung by a leafy canopy, which keeps out the sun for the 

 major part of the day. And it is on the almost procumbent branches 

 of such haunts that the females sit and drop their larvae to the 

 ground. 



Contraction and Extension of Breeding Areas. — However suit- 

 able a spot may otherwise be, should the water supply near by dry 

 up and the game go elsewhere, the flies disappear. Some of them 

 must die, whilst the others migrate, chancing the finding of suitable 

 breeding grounds. An augmentation of flies at the permanent breed- 

 ing grounds has been observed. The area of infestation increases in 

 summer and contracts in winter in accordance with the drying up 

 of the non-permanent supplies of drinking-water far the game. The 

 contraction is also lai^g-ely influenced by a further factor. 

 G. j)allidipes has been found to be particularly sensitive to both 

 extremes of heat and cold, and cannot live through the winter at 

 many summer breeding grounds, because these become too cold. 

 Hence it follows that its winter habitat is not co-extensive with 

 permanent waters in the belt. The permanent breeding grounds have 

 only been found in those places where the heat of the day is not 

 altogether dissipated overnight, and where there is not that marked 

 fall in the night temperature which takes place at some extension 

 breeding grounds and many permanent waters. 



Control of G. j)allidipes'. — It is reasoned that with the mapping 

 out of the winter resorts of this fly, it will be found a practical 

 matter to so deal with these places by prophylactic measures that 

 the fly can be caused to die out and the summer radiation inhibited. 

 In other words, by rendering these winter foci unsuitable to fly- 

 existence, the summer expansion can be artificially controlled, and 

 such control is only limited by the practicability of applying prophj^- 

 lactic measures to all winter resorts. 



A Hypothesis. — That tsetse flies become eradicated over large 

 tracts of the Union coincident with rinderpest outbreaks in the fly- 

 belts is established, but it has long been equally obvious that the 

 decimation of the game was not the only contributing factor. Unfor- 

 tunately, one can only speculate upon what other factors may have 

 played a part in the absence of the essential data. The problem of 

 nagana is so intricate an association — fly trypanosome-game 

 topography — that many of its phases seem inexplicable. Mr. Harris 

 is led to surmise the loss of infection, however, by the majority of 

 the wild mammalian hosts of the trypanosome. The hypothesis is 

 presented that a loss of infection occurs when the host becomes 

 separated from fly-contact, and the possibility is advanced that this 

 may occur frequently with such animals as spend the winter away 

 from the haunts of the fly ; in short, that the protozoan exhausts. 



