206 J. W. SCOTT MACFIE. . 



blood visible througli the walls of the abdomen . It was necessary for me to feed the 

 insects on my own blood, and it should therefore be mentioned that throughout the 

 period of the experiments I was taking five or ten grains of quinine daily. 



Length of Life. 



No true estimate of the natural length of hfe of mosquitos can be expected from 

 laboratory experiments, for the insects are on the one hand protected from their 

 natural enemies, and screened from exposure, but on the other hand they are confined 

 to a restricted space, and in the case of the males are fed on an unnatural diet. In 

 my experiments none of the mosquitos reached the age limits recorded for this species 

 by other observers. The males lived relatively short lives, the longest noted being 

 only 28 days ; and the females, although they survived somewhat longer, did not 

 in a single instance Hve beyond the 62nd day. Patton and Cragg (1913)* state that 

 " The female can be kept alive for many months, and in nature can probably sur\ave 

 for at least six months," but as the conditions determining the length of natural life 

 must be very complex this must be at best an intelligent guess. It was noticed in 

 my experiments that several females showed marked signs of senescence after they 

 had laid a number of batches of eggs. The evidences which I interpret as being those 

 of senility were diminished activity, and reduction of the powers of flight. Mosquitos 

 that had been under observation a long time became very lethargic. They were 

 often noticed to remain resting in the same position all day, and were with difficulty 

 roused. When forcibly disturbed they responded only by crawling slowly to another 

 part of the jar. Towards the ends of the experiments they appeared to be incapable 

 of flight, and either crawled about laboriously, or sometimes made little jumps as 

 though they wished to fly but were unable to do so. If water was in the jars the loss 

 of the power of flight led to the mosquitos falling on to its surface, and being unable 

 to extricate themselves. It was necessary sometimes to guard against this by re- 

 placing the water by damp blotting paper, as it was found the insects might survive 

 in this condition for a considerable time (see Expt. No. vi). In nature they would 

 probably have fallen an easy prey to natural enemies long before such pronounced 

 senile changes had developed. The rapidity with which one batch of eggs followed 

 another, as well as the actual number laid, appeared to be important. For instance the 

 female in experiment No. iii. which laid fifteen batches at intervals of about three days 

 died on the 50th day, but that in experiment No. ii. which laid only ten batches at 

 rather longer intervals survived until the 60th day. 



Blood Feeding. 



The male Stegomyia fasciata feeds on honey only. He can, however, live at least 

 ten days in jars containing nothing but water (see Expt. No. viii), and is able to fertihse 

 the female without taking any nourishment. The female also feeds on honey during 

 the first day or two of her imaginal life, and if blood feeds are denied her may continue 

 to survive on this diet for a long time. Goeldi is quoted by Boyce (191 l)t as having 

 succeeded in keeping a female alive on honey for 102 days. But under normal 

 conditions it must be very exceptional for a mosquito such as Stegomyia fasciata, 



* Patton, W. S., and Cragg, P. W., " Medical Entomology," p. 217. 

 t Boyce, Sir R. W., " Yellow Fever and its Prevention," p. 287. 



