FLUCTUATIONS IN NUMBERS 47. 



twelve hours, or four hours exposure to sun have, alone, 

 very little effect, if the pupae were submerged one night 

 and exposed to sun next day only one per cent, developed 

 into flies ! 



Besides variations in numbers of the fly due to climatic 

 conditions, I found in 1914 interesting variations that 

 were very puzzling. The small islands Bulago, Kimmi, 

 Tavu and Ngamba were each visited weekly from the 

 camp on Kome, and catches were made of flies at the 

 same spots around the coast. 



It soon became obvious that the numbers of flies (as 

 estimated by the number of males caught per boy per 

 hour) on each of the four islands did not vary concurrently, 

 and that variations did not affect the sexes in the same 

 way on the same island (see Charts V and VI). 



On Bulago, for instance, on the south point and west 

 shore the two sexes on the whole varied together, but 

 on the shore of the north bay they varied inversely. 

 In the forest of the north point the variations in number 

 of the males were very great, while the number of females 

 kept very constant. On Kimmi it was noted that the 

 catches from two localities on the north and north-west 

 shores of the island, taken together, varied inversely to 

 the catches from the south and south-east shores, though 

 this was less marked after the beginning of July. This 

 must mean that at certain times the male flies found the 

 north shore more congenial, whereas at others they 

 congregated on the south side of the isle. 



By charting together the figures representing the 

 average catch per boy per hour of males and females for 

 each of the four islands, a curious and interesting point 

 was brought to light. 



On the island where the number of males shows the 

 greatest fluctuations the female figure shows least, and 

 vice versa, and the same was found to hold good for 

 individual localities on Bulago Island. On Tavu Island 



