260 



W. A. LAM BORN. 



and indeed every day or two a fly comes out from among them. The discrepancy 

 in the accounts given by other workers as to the length of pupation (47 to 53 days, 

 Kinghorn, in Bull. Ent. Ees., ii, p. 295 ; and 23 days on an average, Lloyd, in 

 Bull. Ent. Kes., iii, p. 95) would seem to support the conclusion. In February of 

 this year (the wet season), a family of flies {Sarcophaga sp.), which I bred from one 

 parent with a view to studying parasites, all emerged on the same day and at the 

 same hour, whereas from the pupae of a second family bred recently in the dry 

 season only five out of twenty-three have as yet come out, and those three weeks 

 ago ; this strongly suggests that aestivation is proceeding. On the west coast of 

 Africa it certainly occurred in the case of a Muscid allied to Lucilia, and was of 

 course the regular occurrence with various species of Lepidoptera. 



Flight Experiments. 



In passing from a morsitans area into country apparently free from them, whether 

 bush or open country, it has always seemed to me that the same tsetses which have 

 been hovering round continue to follow for a considerable distance. With the object 

 of deciding whether such flies do really attend one and are not chance new-comers^ 

 a series of experiments have been conducted^ consisting in liberating marked flies 

 at a definite point, and then after a walk to various distances capturing all those 

 in the immediate neighbourhood. 



The results obtained afford positive information on the point, but in regard to 

 the actual numbers of the flies recaptured there are of course several conceivable 

 fallacies. For instance, possible variation in the walking pace on each occasion, 

 though it was as uniform as possible ; possible impairment of the insects' powers of 

 flight, as a result of injury during capture ; the influence of wind and of climatic 

 conditions on each occasion, etc. 



The first series of experiments, which I give below in table form, was conducted 

 in the neighbourhood of Domira Bay and consisted in releasing the flies where most 

 were originally taken, in palm country towards the east, and then returning to the 

 Lake shore, a distance of 2J miles, mostly across dambo [open grass land] and 

 capturing as many as possible. On every occasion a breeze was blowing from the 

 direction in which my party was proceeding. 



Date. 



No of males 



released. 



No. of males recaptured. 



2. iii. 15 . 

 3. iii. 15 . 

 5. iii. 15 . 

 6. iii. 15 . 

 8. iii. 15 . 

 9. iii. 15 . 





20 

 20 

 20 

 20 

 20 

 20 



3 



1 



4 



3 



1 

 2 



