BIONOMICS OF TSETSE, ETC., IN THE GOLD COAST. 205 



In all, ten experiments were tried to test how far tsetse will follow a herd of game — 

 five original and five repeats. Fifty tsetse (G. submorsitans) were used in each 

 experiment. A herd of cattle passing along a road was selected and the tsetse were 

 liberated in the centre of the herd. In the first set of experiments, the tsetse were 

 not molested, but it must be remembered that cattle are much easier victims to tsetse 

 than are wild game. In the second set, a number of boys with fly switches were 

 ordered to keep disturbing the flies when seen to alight. 



The results of these experiments are as follows : — 



After one mile (1) 21 were recaptured. (6) 29 were recaptured. 



„ two miles (2) 10 „ „ (7) 17 „ „ 



„ three „ (3) 7 „ „ (8) 12 „ 



„ four „ (4) 3 „ „ (9) 7 „ 



„ five „ (5) „ „ (10) „ 



From this series of experiments it will be seen that after five miles have been 

 traversed the tsetse have either all managed to feed, or have given up the attempt 

 and disappeared. 



VI. Trapping of Glossina. 



The question of how to diminish the number of tsetse in any definite locality is of 

 paramount importance. It has repeatedly been shown that in the case of villages 

 a clearing of about 400 yards around the outer circumference of the village will 

 practically restrict the tsetse to a region outside this area. This, as Mr. T. E. Fell 

 has pointed out, should be undertaken only when such a clearing can be maintained, 

 otherwise a lower, shorter and more scrubby type of vegetation will arise which is 

 very suitable for the flies. The same must apply to fords of rivers and the main roads 

 in a district. This then should be undertaken only in definite localities where the 

 supply of labour is adequate. In a restricted area, as for example the Island of 

 Principe, such a scheme as systematic trapping has had very beneficial results ; but, 

 in wide areas, such as any of the colonies of West Africa, the conditions are totally 

 different. Take, for example, a small portion of the River Volta between Yeji and 

 Yapi. After a week's examination of this part of the river, I am confident in saying 

 that there is not one half mile in this whole area where G. tachinoides is not to be found 

 in quantity. There is a constant stream of canoes plying on the river, and it is now 

 certain that tsetse follow these canoes considerable distances. My own experiments 

 have shown a distance of seven miles, and this cannot be regarded as the maximum. 

 Consequently, to attempt to clear this region of tsetse would mean expense out of all 

 proportion to the advantage gained, because the supply on either side would con- 

 stantly tend to repopulate the whole area. 



At the Yapi ferry I posted five men for four months for the purpose of ascertaining 

 if there would be any diminution in the number of tsetse at the end of that time. 

 The following are the results : — 



lst-23rd Sept. 1915, 2,876 tsetse caught or 125 per day. 

 lst-31st Oct. 1915, 3,526 „ „ or 114 „ „ 



lst-30th Nov. 1915, 3,497 „ „ or 116 „ „ 



lst-23rdDec. 1915,2,985 „ „ or 129 „ „ 



