34 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 
area. The approximate average numbers of organisms per cubic centi- 
meter in breeding places having more than one larva per dip were as 
follows for the br eeding seasons of 1928 and 1929, respectively: Total 
plankton, 8,600 and 6,300; flagellates, 5,400 and 4,200; diatoms, 1,800 
and 500; green algae (other than flagellate forms) , 700 and 900. Pres- 
ent in smaller numbers were the ciliates, blue-green algae, and amoe- 
boid protozoa, although the first two were fairly abundant at times. 
The four principal genera among the flagellate forms were Euglena, 
Chlamydomonas, Trachelomonas, and Phacus, which composed about 
75 percent of the total organisms in this class in the places of high 
larval density. The report of studies made by Boyd and Foot (24) 
shows a similar plankton content in the surface waters at Edenton. 
A classification of ponds in which the abundance of desmids is used 
as an index to the suitability of the water for specific anopheline 
breeding has been suggested by Frohne (57). 
In rearing the larvae in the laboratory various foods may be utilized, 
both those from the natural breeding places and artificial foods such 
as yeast. Barber (3) found that Anopheles quadrimaculatus could 
be reared to maturity on cultures of single species of organisms, in- 
cluding algae, bacteria, or infusoria, and that dead organic material 
was less suitable than living organisms. Komp (/08) reared Ano- 
pheles in a food culture made from Spirogyra killed by heating. 
Boyd, Cain, and Mulrennan (23) report that the infusoria develop- 
ing in a ripened hay infusion, when supplemented by yeast, forms 
an almost ideal food for the larvae, as it invariably produced large 
and healthy individuals. The ripening process requires at least 30 
days in the summer, as the infusions must pass through a period of 
acid fermentation before they are satisfactory as a food supply. 
These authors found that the largest proportion of the larvae reached 
maturity at about 70° F. At this temperature development from 
egg to imago required about 21 days (22). Crowell (44) found that 
the larvae could be reared successfully on powdered dog biscuit. This 
Is a convenient food to use and does not require a ripening process 
or a change of water in the rearing pans. This author also reported 
that, in an insectary maintained at a temperature of about 75° F., 
the larval period ranged from 16 to 24 days, with an average duration 
of each of the four instars of 4, 5, 5. and 6 days. The pupal stage 
required from 60 to 72 hours. At high summer temperatures, with 
an ample food supply, larval development under natural conditions 
may be completed in about 1 week, although some larvae develop more 
slowly than others under the same conditions. With a minimum of 
3 or 4 days for the other aquatic stages (egg and pupa) and about 4 
days for the preoviposition period, the minimum time for a complete 
generation would be 14 or 15 days. At low temperatures or with 
scanty food supply the developmental cycle is greatly prolonged. 
ANOPHELES CRUCIANS Wied. 
The crucians group is now known to include three closely related 
forms which are very similar in the adult stage but differ in larval and 
pupal characters. Two of the forms were described by King in 1939 
(95) as varieties of Anopheles crucians (bradleyi and georgianus) , 
but it was believed that all three represented distinct species, and 
they are recognized as such by the present authors. 
