200 



DR. JAMES J. SIMPSON. 



and 32 females, and expressed his opinion that if this last batch of flies had been taken 

 some 20 miles upstream the females would have outnumbered the males to a much 

 greater extent. 



Dr. J. B. Davey (Bull. Ent. Res., i, p. 145) states that of 117 G. brevipalpis captured 

 during the evenings at Kaporo in Nvasaland, all were males, whereas of seven caught 

 in the same place about mid-day four were males and three females. 



Bequaert gives a further reason for the disparity in proportion of sexes, and in 

 discussing G. palpalis says that in inhabited regions the sexes are in about equal 

 numbers, whereas in uninhabited regions there is a distinct preponderance of males. 

 He says this may be due to the fact that food supplies are more scarce in the latter 

 districts and therefore the more active male is more in evidence. 



Kinghorn and Montgomery report the following catches of G. palpalis on the island 

 of Matondwi, near the southern shore of Tanganyika :— 



3 ? 



July 1,282(91 %) 127(9 %) 



November 396(98-8%) 5 (1'2%) 



Newstead (Report S. S. Comm. of Royal Society, No. 15) gives the following table 

 with regard to G. morsitans. 



Month. 



No. of Days 

 Flies examined. 



Total 

 Flies. 







Meteorological 

 Condition. 



August 7-29 



7 



87 



80-5 



19-5 



Very dry. 



Sept. 1-30 . . 



22 



346 



81-6 



12-4 



j; >> 



Oct. 1-16 



11 



206 



90-8 



9-2 



>» »> 



Oct. 17-31 . . 



11 



165 



68-5 



31-5 



Very heavy rains 



Thus we have such hypothetical reasons to explain the disparity in the proportion 

 of sexes, as (1) the size of the river on which the tsetse were caught, (2) the time of 

 capture, (3) the number of inhabitants in a given area, and (4) the season of the }^ear 

 and meteorological conditions.* 



To all of these I paid special attention during my recent tour. As, however, at 

 certain times I was in an area where G. tachinoides predominated and at others where 

 G. submorsitans predominated, I was unable to make a consecutive study of either. 



The number of days spent in collecting as a basis for percentages has a very direct 

 bearing on the validity of such deductions ; e.g., at Yapi from 1st to 12th June, 1916, 

 856 males and 767 females were caught. This works out at 52.8 per cent, of males 

 and 47.2 per cent, of females. Now let us break up this period into three shorter 



* [A much more probable explanation of this disparity has been given independently by 

 LI. Lloyd (Bull. Ent. Res., iii, p. 235) and W. A. Lamborn (Bull. Ent. Res., vi, p. 250 ; 

 and vii, p. 39). — Ed.] 



