BIONOMICS AND ECOLOGY OP NEARCTIC SPECIES 
87 
preyed upon by a great variety of pre¬ 
daceous and parasitic forms of animal and 
plant life, which in the aggregate take a 
large toll of these and other mosquitoes. 
Certain aquatic plants have also been cred¬ 
ited with deterrent as well as larvicidal 
properties. For summaries dealing with 
these, the reader is referred to works of 
Howard, Dyar, and Knab (1912-17a), Boyd 
(1930a), Matheson (1930), and Hinman 
(1934a). The most important enemies of the 
larvae are the small insectivorous fishes of 
the family Poecilidae, which actively search 
for their prey in shallow water amongst 
vegetation and debris (Rockefeller Foun¬ 
dation 1924). In the Southern States the 
most important species is Gamiusia pa- 
truelis (affinis). There can be no doubt 
about the influence of these minnows in 
limiting mosquito breeding in areas where 
they abound, and ecological studies on the 
occurrence and abundance of mosquito 
larvae in various locations must always 
take into consideration their presence or 
absence, as well as the amount of protection 
against them afforded by plants and debris. 
A review and discussion of the use of fishes 
in mosquito control has been published by 
the International Health Board (Rocke¬ 
feller Foundation 1924). Of the aquatic 
insects, the nymphs of damselflies and 
dragonflies (Odonata), water scorpions 
(Ranatra spp.), baekswimmers (Notonec- 
tidae), and the larvae of water beetles, 
particularly those of the family Dytiscidae, 
are frequently noted as preying on anoph- 
eline larvae. 
Aquatic plants of the genus Utricularia 
trap mosquito larvae by means of small 
bladders and have been observed to be 
rather efficient in reducing a larval popula¬ 
tion, particularly in aquaria (Matheson 
1930). 
While these predaceous forms must 
destroy countless numbers of larvae, never¬ 
theless it is true that they may all be found 
in association in even the heaviest of anoph- 
eline breeding areas, so the final result 
appears to be merely a natural balance. 
Certain types of waters are undoubtedly 
eliminated as breeding places for anophe- 
line larvae because of the presence of 
their natural enemies, and control efforts 
can sometimes be aided materially by 
changing conditions in favor of these 
predators. 
