100 Parasitic Arthropoda 



mouth-parts, legs, and wings of the future adult are now external, but 

 enclosed in chitinous cases. On the upper surface, near the base of 

 the wings are two trumpets, or breathing tubes, for the pupal spiracles 

 are towards the anterior end instead of at the caudal end, as in the 

 larva. At the tip of the abdomen is a pair of large chitinous swim- 

 ming paddles. 



As illustrative of the life cycle of a mosquito we shall discuss the 

 development of a common house mosquito, Culex pipiens, often 

 referred to in the Northern United States as the rain barrel mosquito. 

 Its life cycle is often given as t3rpical for the entire group, but, as we 

 have already emphasized, no one species can serve this purpose. 



The adults of Culex pipiens hibernate throughout the winter in 

 cellars, buildings, hollow trees, or similar dark shelters. Early in 

 the spring they emerge and deposit their eggs in a raft-like mass. 

 The ntimber of eggs in a single mass is in the neighborhood of two 

 hundred, recorded counts varying considerably. A single female 

 may deposit several masses during her life time. The duration of 

 the egg stage is dependent upon temperature. In the warm summer 

 time the larvas may emerge within a day. The larvae undergo four 

 molts and under optimum conditions may transform into pupae in 

 about a week's time. Under the same favorable conditions, the pupal 

 stage may be completed in a day's time. The total life cycle of Culex 

 pipiens, tmder optimum conditions, may thus be completed in a week 

 to ten days. This period may be considerably extended under less 

 favorable conditions of temperature and food supply. 



Culex pipiens breeds continuously throughout the siunmer, 

 developing in rain barrels, horse troughs, tin cans, or indeed, in any 

 standing water about houses, which lasts for a week or more. The 

 catch basins of sewers furnish an abundant supply of the pests under 

 some conditions. Such places, the tin gutters on residences, and all 

 possible breeding places must be considered in attempts to extermi- 

 nate this species. 



Other species of mosquitoes may exhibit radical departures from 

 Culex pipiens in life-history and habits. To control them it is essen- 

 tial that the biological details be thoroughly worked out for, as. 

 Howard, Dyar, and Knab have emphasized, "much useless labor and 

 expense can be avoided by an accurate knowledge of the habits of the 

 species." For a critical discussion of the known facts the reader is 

 referred to their monograph. We shall confine ourselves to a few 

 illustrations. 



