BIONOMICS OF TSETSE, ETC., IN THE GOLD COAST. 199 



course numbers of them must be bitten ; but although the river banks everywhere 

 abound with baboons and monkeys, I think it highly improbable that these form a 

 source of food supply. I kept two Cercopithecus patas for nearly two years, and never 

 once did I see a tsetse manage to feed off them. Even when apparently asleep, the 

 monkeys at once disturbed the tsetse on alighting, and in the great majority of cases 

 succeeded in catching and devouring them. There is, however, one small mammal 

 which is extremely abundant on the banks of the Volta River, and that is a large 

 yellowish brown bat. These animals sleep during the day in a suspended position in 

 the dense overhanging trees in localities similar to those where G. tachinoides abound, 

 and I am inclined to think that, apart from the human supply, these animals are the 

 chief source of the mammalian blood supply. 



I carried out a large series of experiments to find out whether tsetse ever imbibe 

 water, but in none of these could I definitely say that such was the case. I used 

 several tubes containing citrated blood, pure water and various coloured liquids, 

 each covered with a membrane of rat's skin. Although at different times tsetse pierced 

 each of these membranes, in no case could I say that any liquid was imbibed except 

 the fresh blood. Never have I seen a tsetse drink an exposed liquid. G. tachinoides, 

 just like G. morsitans, seems to prefer piercing before sucking. Several experiments 

 with fruit, e.g., ripe pawpaw, mangoes, and ripe marrows also proved negative. 

 Although the tsetse were seen to pierce the skin, never did I actually see any liquid 

 being absorbed. 



The percentage of mammalian blood to non-mammalian differs greatly in the case 

 of G. submorsitans. 



Out of 987 tsetse examined with discernible blood in the stomach, only 23 con- 

 tained non- mammalian blood, i.e., only 2*3 per cent. The reason for this is not far 

 to seek. In the open country away from water where G. submorsitans abounds, 

 there is practically no reptilian fauna, so that it is lack of opportunity rather than 

 preference which decides the matter. To test this I put large numbers of G. sub- 

 morsitans into cages with different reptiles and nearly all fed voraciously and had 

 distended abdomens, especially in the early morning. 



A point of interest which obtruded itself on me on several occasions was that when 

 an animal had been shot, tsetse and Tabanids often alighted on the carcase. Although 

 the Tabanids frequently drank from the open wound, tsetse were never seen to do this, 

 but always pierced the skin, and so imbibed. This leads one to suppose that G. sub- 

 morsitans never drinks exposed liquids. 



IV. Disparity in the Proportion of Sexes in Glossina. 



The question of the disparity in the proportion of sexes in Glossina has attracted 

 the attention of many observers in various parts]of Africa. 



Dr. R. E. McConnell (Bull. Ent. Res., iii, p. 58) was impressed by the apparent 

 marked numerical superiority of males along the large rivers, and of females on the 

 smaller streams. He quotes as an example that of 40 specimens of G. palpalis 

 (fuscipes) taken in October on the Nile, 35 were males and 5 females, while of 77 

 taken in July 67 were males and 10 females. He goes on to point out that of 56 flies 

 captured in September near the mouth of small tributaries of the Nile 24 were males 



