i66 N. J. Agricultural Experiment Station, Bulletin 348 



disappearing density to the north and west, a more slowly diminish- 

 ing density to the south and east, and the greatest density in the 

 areas facing the gaps which lead from this valley to the south and 

 east. 



Inasmuch as the fresh-water swamp mosquito by this date had had 

 time to effect its distribution: (a) the low and rapidly decreasing 

 density to the north and west may be taken to indicate that move- 

 ment in that direction was slight; (b) the more slowly decreasing 

 density to the south and east may be taken to indicate that the move- 

 ment in this direction was more pronounced; (c) the greater and 

 more slowly decreasing density in the areas which face the gaps 

 leading from this valley to the south and east may be taken to indi- 

 cate that the principal movement occurred through these gaps. 



Cause of Mosquito Flight 



The cause of mosquito migrations is obscure, but it is safe to as- 

 sume they are in some way related to one or both of the great neces- 

 sities of living matter — persistence of the individual and the repro- 

 duction of its kind. 



The mosquito emerges, its body wall hardens, its parts become 

 adjusted, and it flies away in search of food and opportunities for 

 reproduction. Usually these desired conditions are found nearby. 

 The female alternates between places where food may be had and 

 places where eggs may be laid. 



This is the type of movement exhibited by the mosquitoes that 

 breed about human habitations (the house mosquito), and the under- 

 lying causes are very evident. 



When the same species breeds intensely on a very large area, it 

 tends to move from the place of breeding and may cover in some 

 cases a distance of 2.5 miles. The movement must be made in 

 response to a desire for food, because opportunities for reproduction 

 are unlimited. No doubt the specimens that find food near the place 

 of birth return to the source for reproduction, but those which mi- 

 grate farther for food find breeding spots nearer the source of food 

 supply. There is no evidence to indicate that this movement of the 

 house mosquito takes place rapidly, but the facts in hand point 

 rather to a slow dissemination. 



When dealing with a species that lives in the wilds, such as the 

 more important Anopheles (malaria-carrying kinds), the movement 

 to secure food may take on a very different character. LePrince 

 and Orenstein have shown that Anopheles albimanus and others 



