ENTOMOLOGY 273 



the fact that not more than lo per cent of the ground was covered 

 by continuous forest. The clearing, which varies in width up to 

 about a mile, was begun in 1932, and by 1934 had been extended 

 to a length of some thirty-five miles. Indications to date show that 

 it has been remarkably effective: trypanosomiasis has died down 

 to near the vanishing point on the Rhodesian side of the border, 

 and several evacuated farms have been reoccupied with consider- 

 able numbers of cattle. 



Southern Rhodesia has a specific Tsetse Fly Act (1929), which 

 empowers the Government to control traffic leaving the fly area 

 and to rid it of any accompanying flies. On routes which carry 

 wheeled traffic, suitable chambers are erected for the treatment 

 of motor vehicles with petroleum-pyrethrum sprays. There is a 

 gauze-covered ante-chamber, in which any flies which leave the 

 vehicle can be caught. On routes carrying only pedestrian and 

 cyclist traffic, smaller gauze cages are provided and native guards 

 are on duty at each station. Fourteen such stations have been 

 established, but with the gradual retrogression of the fly, three have 

 already been discontinued, and there is a prospect that six or seven 

 more will follow at an early date. 



Whilst the measures put into operation against the encroach- 

 ment of G. morsitans in the territory have been conspicuously effec- 

 tive, the constant destruction of wild life is highly repugnant, and 

 it is felt in Southern Rhodesia that every effort should be made to 

 discover alternative measures which can be used gradually to 

 replace the game cordon, now that the flies' advance has been 

 controlled. Field work in the nature of superficial observations, 

 but including the discovery of the natural breeding sites of G. morsi- 

 tans, has been proceeding in the colony during the past quarter of a 

 century, whilst more detailed work in reference to the bionomics 

 of the fly, studying the effect of delayed and controlled grass fires, 

 seeking measures of biological control, testing the Harris and other 

 traps and so forth, has also been carried out from time to time. 

 Funds have now been provided for continuous laboratory research 

 into the effect of environmental factors, particularly temperature 

 and humidity, on the vital processes and behaviour of the local 

 tsetse. Most of the necessary apparatus has now been assembled at 

 Salisbury, and some progress has already been made. It is hoped 



K 



