BIONOMICS AND ECOLOGY OP NEARCTIC SPECIES 
85 
the larval microhabitat itself or in the gen¬ 
eral area. It is now known that the read¬ 
ings may vary considerably in different 
types of vegetation in the same pond, and 
also at different times of the day. 
Dissolved gases. Boyd (1929b) reported 
a considerable variation in the amount of 
dissolved oxygen in various anopheline- 
breeding waters in North Carolina, the 
range being from 0.1 to 14.0 p.p.m. No 
larvae were found in waters devoid of this 
gas. Fairly high concentrations of carbon 
dioxide appeared to favor breeding of A. 
quadrimaculatus whereas waters with lower 
concentrations favored A. punctipennis, 
although breeding of both species occurred 
in the absence of this gas. Studies on the 
effect of ammonia in breeding waters in this 
country are lacking. In India, Senior- 
White (1928) found saline ammonia in 
excess of one part per million usually in¬ 
hibitory to anopheline breeding, and Beat- 
tie (1932) in Trinidad found that larvae 
of A. tarsimaculatus were more numerous 
when the ammonia nitrogen content was 
low. 
Specific aquatic environments. A. quad¬ 
rimaculatus breeds chiefly in ponds, pools, 
lake margins, swamps, and miscellaneous 
water collections of a more or less perma¬ 
nent nature where aquatic vegetation or 
surface debris are present in abundance. 
It usually occurs more intensively in open, 
sunlit waters than in shady places. This 
apparently is not due to any inhibitory 
effect of shade but to the fact that vegeta¬ 
tion on which the larvae depend for food 
and shelter becomes scarce in absence of 
sunlight. 
A. punctipennis is the most widely dis¬ 
tributed of our anophelines and breeds in 
a great variety of places. Margins of flow¬ 
ing streams, pools in intermittent stream 
beds, springs, ponds, and pools, artesian 
wells, artificial water receptacles, and new 
borrow pits and other excavations are noted 
as breeding places of this species. It is 
often associated with A. quadrimaculatus 
in the more permanent waters. It has been 
noted as the first anopheline to occur in 
certain rain or flood pools when micro¬ 
organisms are scarce, and to be replaced 
by A. quadrimaculatus as a richer flora and 
fauna develop. Cool, clean water free 
from the products of organic decay is, in 
the opinion of most writers, most suited to 
the species. Carpenter (3939), however 
thought that they tolerate more filth in 
their breeding places than other anophe¬ 
lines in Arkansas. 
A. crucians breeds in ponds, lake mar¬ 
gins, swamps, and pools of both an inter¬ 
mittent and permanent character and is 
often associated with A. quadrimaculatus 
and A. punctipennis in such places. It is 
often the only anopheline present, however, 
in acid waters such as occur in cypress 
swamps in Florida and southern Georgia. 
Metz (1918) has reported that the species 
apparently can subsist in nature on a diet 
primarily of decaying vegetable matter, as 
the larvae were found by him in enormous 
numbers in water contaminated by sulfuric 
acid wastes, having scanty microscopic flora 
and fauna but rich in small particles of 
disintegrated plant tissue. 
Larvae of the A. maculipennis group 
breed in a variety of situations. In Cali¬ 
fornia Freeborn (1926) reports them as 
occurring in shallow sunlit pools of clear 
water, preferring those having mats of 
green algae, and states that hoof prints, 
wayside pools, neglected irrigation and 
drainage ditches, and seepage areas furnish 
the most favorable locations. In New 
Mexico Barber and Forbrich (1933) found 
the species to prefer completely shaded 
situations and to occur with increasing 
scarcity as illumination increased. In Min¬ 
nesota Owen (1937) found A. occidentals 
more often in semipermanent and perma¬ 
nent ponds along the shoreline in the pres¬ 
ence of vegetation, although it also occurred 
in a variety of other locations. He reports 
it as breeding in association with A. punc¬ 
tipennis and A. quadrimaculatus. 
A. walkeri breeds in swamps having a 
thick growth of emergent aquatic vegeta¬ 
tion, cattail ponds and lake margins appar¬ 
ently being the most favored habitats. It 
has also been reported by Komp (1926) 
from rice fields and from water covered by 
