116 RUPERT W. JACK. 



extremely scarce.* Fly appears to be extremely numerous and is certainly extremely 

 pertinacious. Half-a-dozen flies that are eager for blood give a far greater impression 

 of numbers than half-a-dozen " following " males. Fifty or sixty really hungry flies 

 would give the impression of hundreds. Several investigators have indeed drawn 

 attention to the fact that the numbers of tsetse under such conditions may be more 

 apparent than real. The writer can only speak with experience of one locality of 

 this nature (Gorai Kiver, Lomagundi), but a noteworthy point was the extreme 

 locahsation of the fly, few being met with except at the point where the path crossed 

 the watei:-course, and here they seemed to swarm. When the WTiter camped at this 

 spot for several days, the flies became very much less troublesome. Many pre- 

 sumably fed on the two dogs accompanying the party, and a few on the natives. 

 Some 80 odd were caught, and the party was then left in comparative peace. No- 

 where else in the dried-up triangle of country formed by the Hunyani and Ambi 

 Rivers with the escarpment were flies met with in any numbers. 



The following April no fly was encountered at the river crossing, but they were 

 present in the neighbouring mopani forest in very moderate numbers, giving the 

 impression of a decrease since the previous November. In regions such as this it is 

 judged that the wet season must constitute the main breeding period, owing to the 

 return of game with the rains, but that under these conditions the fly does not attain 

 the same numbers as in areas where more favourable winter haunts are found. The 

 visitor in the dry season meets, however, a large proportion of the fly population at 

 once, whereas if game is plentiful he probably meets only a fraction. 



This argument may not apply universally to localities where fly seems numerous 

 and game very scarce. In the area referred to it was actually shown that game was 

 moderately plentiful when the country was not dried up. Data for times of year 

 other than the dry season appear to be lacking in respect to most of the classic 

 instances where fly apparently abounded in the absence or extreme scarcity of game. 



During the earUer part of the dry season, in May, June and July, the coldest 

 weather occurs, and there is little doubt that the fly breeds less freely at this time of 

 year and that the pupal period is more prolonged, both of which facts tend to check 

 increase. On the whole, the fly tends to be less numerous at this time of year, 

 particularly in July, but during August and onwards to the advent of the rains con- 

 siderable increase occurs. With the advent of heavy and persistent rains the fly 

 scatters and therefore appears to decrease suddenly, although this is probably only 

 apparent. 



The answer to the question as to whether the dry season is in general a period of 

 stress for the fly or not, except in so far as the breeding is influenced by temperature, 

 would appear therefore to be in the negative as far as conditions similar to those of 

 this territory are concerned, and the writer is of opinion that, excepting certain 

 locahties, far from being a time of stress, the latter part of the dry season is probably 

 the most favourable and important period of the year under normal conditions. 

 Furthermore, it would appear that the later the rains are in commencing, the greater 

 the insects' capacity for increase. That such conditions are not inimical to the fly 



*The writer is largely repeating results obtained by others in Central and East Africa, 

 although observations in S. Rhodesia are entirely in accord. 



