THE TSETSE PROBLEM IN NORTH MOSSURLSE. 329 



Tlie main reptile-population follows closely the two biggest rivers and is not 

 sufficiently intimately connected with the big permanent fly-belts to be worth 

 discussing. In the fly areas I noticed more snakes, including several pufi-adders, 

 on the granite-gneiss than elsewhere. Other reptiles were a large arboreal Varanus^ 

 which occurs in various types of secondary wooding, including Brachystegia, but of 

 which I have seen few individuals in all, and some not very abundant Agamid and 

 smaller lizards in the Brachystegia areas. 



Distribution of the Fly in relation to the Geological Formation. 



The granite-gneiss, with its open-stemmed Brachystegia covering and frequent 

 vleis, is the special home of G. morsitans, which in the dry season is still to be found 

 in numbers and breeding actively beside particular vleis. G. pallidipes is also 

 plentiful there, and G. brevipalpis is found in small numbers where the shade is 

 particularly heavy. 



The basalt, with its sparse stunted bush, was still carrying an extremely thin 

 sprinkling of G. morsitans and pallidipes in late July, when burning was barely 

 beginning. I am inclined to regard it as, in the main, an overflow area from the 

 gneiss, and it is quite likely that any measures that banished fly from the latter 

 formation would incidentally banish it from the adjoining basalt. 



The sedimentary rock area, with its fine Brachystegia forest and considerable if 

 patchy undergrowth, is apparently more or less heavily infested almost throughout 

 with G. brevipalpis. G. pallidipes also occurs, but in small numbers, said to be 

 greater in the rains. 



Of the two woodland sections of the dolerite area the Mafusi-Musapa high-forest 

 section, with its extensions, appears to be more or less heavily infested throughout, 

 at any rate in the dry season, with G. brevipalpis, G. pallidipes also occurring. 

 Pupae of G. austeni were taken in numbers near the Buzi-Mtshanedzi confluence. 



In the Puizisi-Mtshanedzi area on the other hand G. pallidipes, though in small 

 numbers seems rather specially in prominence, perhaps in part owing to the relative 

 absence of the bigger fly. The latter does occur here and there in small numbers 

 wherever the shade is suitable. Behind the Makwiana escarpment the country 

 appeared to be clear of the fly by early August and had probably been so for some 

 weeks, though it would still doubtless be possible occasionally to encounter there 

 an odd straggler carried from below% particularly on the Chikambwe's tributaries, 

 where leaf was present. At the lower elevations, where also the bush of the dolerite 

 retained more leaf, fly was still met with ; but judging from the observations that 

 Dr. Lawrence has most kindly carried out for me since my departure, it would seem 

 that it must become specially scarce there also towards the close of the dry season, 

 though not extinct. It is in part a matter of leaf-fall, for at his station (Gogoyo) 

 pallidipes showed itself once more in some numbers with other biting flies when the 

 leaves were well in evidence again in the hot weather shortly preceding the rains. 

 Glossina brevipalpis was taken in small numbers here and was seen by me also on the 

 Buzi below Spungabera. 



An expedition sent by me to the Chinyika in late September failed to take any 

 tsetses, though it brought back numbers of other bitina: flies. 



