176 STEGOMYIA FASCIATA [CH. 



genus Culex. Miss Mitchell has found them in water at i C. 

 and states that some pupated at 12 C., but in the labora- 

 tory the larvae generally die if the temperature falls to 10 C. 

 It is noteworthy that these low temperatures are more fatal 

 to the fully grown larvae than to the earlier stages. 



If the temperature of the water in which the mosquitoes 

 are developing falls daily below 20 C., the duration of the 

 larval stage may exceed a month. The adults which eventually 

 emerge, moreover, are generally so weak and unhealthy that 

 they are unable to feed and soon die. 



The pupa. The duration of the pupal stage varies from one 

 to five days, after which the adult insect emerges. The pupae 

 are very sensitive to cold and a fall of temperature is almost 

 invariably fatal to them, as their organization is not adapted 

 to withstand the vicissitudes of climate. The pupae resemble 

 those of Culex in their general appearance. 



The duration of the complete life-cycle from the new laid 

 egg to the emergence of the imago maybe as short as n days, 

 but is usually from 15 to 20 days. A prolonged exposure to 

 cold, on the other hand, may increase this period to as much 

 as five months, and as mentioned above, the dried eggs are 

 capable of living for long periods without developing. 



Stegomyia fasciata and disease. In addition to being one 

 of the commonest species of mosquito occurring in the tropics, 

 Stegomyia fasciata is entirely responsible for the transmission 

 of " Yellow Fever." It also has been shewn capable of trans- 

 mitting Filaria bancrofti to man, but as this parasite is more 

 commonly carried by members of the genus Culex, the infection 

 will be described later. 



Ed. Sergent and Neumann have shewn that Plasmodium 

 (Proteosoma) pracox or relicta, parasitic in birds, will develop 

 in 5. fasciata. Finally, Fiilleborn and Mayer, by feeding this 

 mosquito on the blood of animals swarming with trypanosomes 

 and subsequently, after short intervals, on normal animals, 

 have succeeded in the mechanical transmission of Trypanosoma 

 gambiense. It is very doubtful, however, whether in nature 

 S. fasciata ever carries sleeping sickness, and in any case such 

 transmission can only be very exceptional. 



