262 THE MOSQUITOES OF NEW JERSEY 



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

 that they are in some way related to one or both of the great necessities 

 of living matter — persistence of the individual and reproduction of its 

 kind. 



When the mosquito emerges from its pupal skin, its body wall hard- 

 ens, 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. 



It seems likely that such simple type of spread is apt to be radial 

 but there is no data to prove the point. 



In a species that lives in the wilds, such as the more important species 

 of Anopheles the movement to secure food may take on a different char- 

 acter. LePrince and Orenstein (17) have shown that An. alhimanus and 

 others make their way for a distance of over a mile to a village, appar- 

 ently in search of food, and that they or others of the same species 

 make a return flight before morning. This does not sound like a case 

 of radial distribution, but more like a directive movement to a definite 

 point for a definite purpose. 



When dealing with the fresh water swamp mosquitoes, such as A. 

 vexans, breeding intensively over a large area, tlie outward movement 

 as shown by J. Lyell Clarke, chief executive of Desplaines Valley Mos- 

 quito Abatement District, is definitely radial. Clarke's work was done 

 in a plains country. The author has shown that in broods produced in 

 a hilly country the outward movement is irregular, passage over the 

 mountains taking place through the gaps and migration proceeding 

 farther in the direction of great populations. 



As has been shown, carbon dioxide is a powerful attractive agent. 

 Green plants void carbon dioxide at night and the human kind at all 

 times. Since the population as well as the factories of great cities are 

 producing vast amounts of carbon dioxide, it seems logical that mosqui- 

 toes might be drawn to these cities and the usual migration pattern 

 characteristic of the open country be considerably modified. 



A warm temperature, 80°F., is extremely favorable. Light is avoided 

 by most species and some have such abhorrence of it that they will not 

 become active while it is strong. Atmospheric moisture has a very pow- 

 erful effect upon the adult. High percentages are favorable and low 

 percentages deadly. Rain itself is decidedly injurious and prevents mos- 

 quito activity. 



Air movement also greatly influences mosquito activity. A stiff breeze 

 is usually quite suflicient to stop their movements and to compel them 



