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



201 



periods, say 1st to 4th June, 5th to 10th June, and 11th to 12th June. The numbers 

 and percentages are as follows : — <J ? 



lst-4th June .. 206 (52'1%) 189(47*9%) 



5th-10th „ .. 523(60-4%) 343 (39'6%) 



llth-12th „ .. 127(35-1%) 235(64*9%) 



Now the enormous disparity in the percentages in these three periods compared 

 with that in the total period is very marked. Consequently, were one to take any one 

 of these short periods as a basis for deduction, the conclusion would not be in any way 

 in accordance with facts over a longer period. 



The longer the period over which observations are made, provided the meteoro- 

 logical conditions are fairly constant, the greater will be the validity of the con- 

 clusions. Again, the larger the number caught, the greater will be the chance of coming 

 to a definite decision. This is almost a truism, but it has been so much overlooked 

 that it is worthy of emphasis here. 



Now let us take some definite cases, e.g., at Yapi. The following are the results 

 of prolonged investigation : — 





<$ 



¥ 



Total No. 

 examined. 



Rainfall. 



June 1914 



70 % 



30 % 







July 1914 



57 % 



43 % 







Sept. 1915 



56-5% 



43-5% 



2,876 



8-34 



Oct. 1915 



46-5% 



53-5% 



3,526 



2-66 



Xov. 1915 



47-5% 



52-5% 



3,497 



nil 



Dec. 1915 



50 % 



50 % 



2,985 



nil 



1-12 June 1916 



47-2% 



52-8% 



1,733 



2-71 



3-12 Sept. 1916 . . 



64 % 



36 % 



183 



[4-63 



It will be seen from the above that the greatest disparity in the proportion of sexes 

 occurs during the period of greatest rainfall. 

 Now at Daboya the following are the results : — 





3 



? 



Total No. 

 examined. 



Rainfall. 



29, 30. iii. 16 



60% 



40% 



142 



1-54 



21, 27. vi.16 



58% 



42% 



907 



5-33 



23, 24.vii.16 



50% 



50% 



215 



5-44 



The results here obtained are almost in direct contradiction with those previously 

 shown for Yapi. 



