GLOSSINA INVESTIGATIONS IN NYASALAND. 39 



Effect of Bush Fires on the Distribution of the Fly. 



On my return to the proclaimed area in the first week in June, I found that the 

 abourers who had been employed in clearing the road nmning west from Domira 

 Bay had fired the grass and that the flames spreading before the southerly breeze, 

 which seems to blow at this season almost constantly from that quarter, had extended 

 right up to the chain of villages along the banks of the Lipimbi to the north, where 

 they had died out at the edge of the clearings round the villages. The result was a 

 marked dimuiution in the numbers of flies in the burnt area, so much so that one was 

 almost free from attack when hunting for pupae, of which a fair number were obtained. 

 But on camping at the spot where on the banks of the river I have stopped previously 

 in comfort for weeks, I was so beset with flies in my tent that I found it necessary to 

 move, and the natives informed me that they were bitten occasionally in the villages, 

 even though there were extensive clearings all the way round. I have no doubt that 

 the flies had come in partly as a result of the fires and partly owing to the driving 

 away of the game. But apart from these flies there were pupae enough under logs 

 untouched by the fires soon to repopulate the burnt area. In the Lingadzi area, 

 which had not been burnt, I was so beset by the fly on proceeding to make artificial 

 breeding places that I gave it up for the time being and fired the grass extensively, 

 the result being that two days later two flies only were encountered. 



I endeavoured to obtain evidence of the retreat of the flies before the flames by 

 shooting some of the birds which are attracted in considerable numbers to hawk 

 insects driven out, but I did not find any tsetses in the stomach contents. 



I may remark incidentally that by obtaining birds under these conditions one finds 

 the stomach absolutely packed, so that ample evidence as to what insects birds do 

 really eat could readily be obtained. 



The flames are not to any extent instrumental in burning up the dead trees which 

 form so large a proportion of the breeding places, the fact being that the fires are too 

 fleeting as a rule to do more than just char most of the logs, which are also protected 

 by dust and by earthy deposits of termites. 



Systematic burning of the grass is not in my opinion likely to be of value for 

 controlling the fly, because over much of the fly country the grass is patchy, so that the 

 fires fail to spread, and in some regions it will not burn till late on in the dry season, 

 when the fly is able to find refuge in areas burnt long before. 



Where the fires have been extensive, most of the game seems to be driven off and 

 to remain for the time being in other parts, with the exception of wart-hog, which 

 then grubs up roots. This animal therefore probably provides food for the newly 

 emerged flies. 



Proportion of Sexes. 



Confirmation has now been obtained of the theory — which as I now see was 

 originaUy advanced by Lloyd (Bull. Ent. Res., iii, p. 235)— that the male flies, the 

 majority of which I have found to be replete and which do not attempt to bite, 

 attend on possible hosts in the anticipation of securing females coming to feed. 

 When the host rests, so that there is less likelihood of the females being attracted, 

 the majority of the flies retire. 



