INSECTS AND DISEASE 



227 



hanging head downwards in the water. The pupa stage is also 

 passed in the water and differs from most insect pupas in being 

 an active " wiggler " as well as the larva. It differs from this larva 

 in having a large head provided with two air tubes for breathing. 

 The adult emerges from the floating pupa skin and is easily killed 

 by any shower that wets its unexpanded wings, or any spray that 

 may be thrown upon it. 

 Our commonest northern mosquito (culex) probably does not 



\ 



FIG. 78. Mosquito eggs and larvae (Theobaldin incident); two 

 larvae feeding on bottom, others at surface to breathe. 

 From Doane. 



transmit disease and may be distinguished from anopheles, which 

 carries malaria, by the fact that the latter stands almost on its 

 head when at rest, while culex holds its body more nearly hori- 

 zontal. Fortunately, stegomyia which transmits yellow fever, 

 is a tropical species of mosquito and does not usually invade the 

 temperate regions. 



Mosquito Control. This outline of the metamorphosis gives the 

 key to the methods of attack which consist of: 



