77 



there was then no difficulty in obtaining a sufficiency of the latter. 

 The relatively small proportion of females that is normally taken is a 

 matter of great interest. In the laboratory the sexes are bred in 

 equal numbers, so that it is fair to assume that they are really equal 

 in nature. Several writers have drawn attention to the fact that the 

 swarms of Tsetse which accompany a moving object leave it as soon 

 as motion ceases .... The majority of the swarm, however, 

 are not desirous of feeding .... If the flies which actually 

 bite are caught, they are found to be females as frequently as males, 

 but the small proportion of females that is caught normally shows 

 that the swarm consists almost entirely of males. An analogous 

 case may be quoted. The vast swarms of midges so often seen on 

 fine evenings are known to consist entirely of males, and directly a 

 female joins the swarm it is mated and the couple drop from the dance. 

 With Glossina, as long as an animal is moving there is a probability of 

 females rising to feed and of the accompanying males thus finding 

 mates. When the animal stands there is little chance of females 

 rising to it, and this may be the reason why the males leave." 



Writing in 1915, with reference to observations made by him in 

 Nyasaland towards the close of the previous year, Dr. W. A. Lamborn 

 (82) states that the reason why "Tsetses are especially attracted by 

 moving objects," and " that several flies will often travel on a person 

 for considerable distances without attempting to bite, is not yet clear, 

 but an examination of 43 individuals taken off the ground on various 

 occasions as they followed showed that all were males, and it seems 

 a reasonable supposition that such flies may be lurking in anticipation 

 of the advent of a female. No courtship takes place, several males 

 often making a simultaneous rush at the female on sight, and one 

 seizing her, pairing takes place in the air, the couple then settling. 

 It is by no means uncommon to take off natives in one's company a 

 couple which have been seen to pair, and several times paired couples 

 have been taken by means of bird-lime smeared on material borne on 

 a native's back." It may be added that, out of a total of 2,460 

 G. morsitans caught by Dr. Lamborn's fly boys in the course of his 

 investigations, 2,040 were males and 420 females, thus confirming the 

 disproportion of the sexes (predominance of males) met with in many 

 fly-belts. 



As regards G. brevipalpis in Nyasaland, Dr. J. B. Davey notes that 

 out of 117 specimens " captured at Kaporo in the evenings in August 

 (dry season), all were males. Seven were captured at the same place 

 and time of year about midday, and of these four were males and three 

 were females." 



Sir David and Lady Bruce, and their collaborators, writing on 

 G. brevipalpis as vector of trypanosomiases in Nyasaland, mention 

 that among 500 flies caught at the mouth of the River Lingadzi, on 

 the western shore of Lake Nyasa, there was not a single female,, and that 

 among several thousand specimens brought to their laboratory, there 

 were only four females. It is suggested that the females remain hidden 

 in dense bush and do not fly outside it as do the males. 



Lastly, Austen (3. 1911) writes with reference to the same species 

 that, out of 359 specimens examined by him, " only 42 were females, 

 and the enormous preponderance of males over females usually seen 

 among captured specimens has been noted both by Stuhlmann and 

 Davey. It is pointed out, however, by the former author that, as in 

 the case of other flies, it is shown by breeding G. brevipalpis in captivity 

 that the two sexes are produced in approximately equal numbers. 



