THE MOSQUITOES OF THE SOUTHEASTERN STATES 7. 
10 or more days, the larval skin is shed four times, each successive 
instar showing a progressive increase in size. The first two instars 
are very small and are easily recognized as immature. In the third 
instar the hairs have fewer branches than in the fourth instar, and the 
sclerotization of the anal segment is less complete. Immature Ano- 
pheles larvae usually have a collar of dark sclerotin around the base 
of the head. 
The food of mosquito larvae consists of minute plants and animals 
and fragments of organic debris, which the larvae strain from the 
water by the action of their mouth parts. Barber (3, 4) reared the 
larvae on pure cultures of various organisms, and concluded that 
the presence of living food organisms was necessary for any consid- 
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Figure 3.—Eggs of mosquitoes: A, Egg raft of Culex restuans; B, egg of Aedes 
taeniorhynchus; C, egg of Anopheles quadrimaculatus, showing floats. (How- 
ard, Dyar, and Knab.) 
erable growth. Hinman (72) has suggested that materials in solution 
and colloids in suspension in the breeding waters may play a part in 
larval nutrition. A discussion of the food of anopheline larvae is given 
in the notes on Anopheles quadrimaculatus. 
With the fourth molt the pupa appears. The pupal stage (fig. 4) 
is also aquatic and is a period of marked transformation, during 
which the adult insect is formed. The imago usually emerges after 
about 2 days. 
The length of life of adult mosquitoes under natural conditions is 
difficult to determine, but for most of the southern species it 1s prob- 
ably only a few weeks during the summer months. Some of the 
northern species of Aedes that emerge early in the spring apparently 
live much longer. Daily observations on abundance following the 
emergence of a large brood of certain species of Anopheles (151 ) and 
