THE MOSQUITOES OF THE SOUTHEASTERN STATES 19 
for larval development, or to aid in biological control. Comprehen- 
sive drainage plans, especially for malaria control, should be prepared 
with the aid of trained engineers. 
Two phases of the drainage problem in mosquito control to which 
attention has been called in recent years are its possible effects upon 
wildlife and upon soil conservation. Through cooperative biological 
studies efforts are being made to determine what measures may be 
applied to large swamp areas, particularly those not close to centers 
of population, which will disturb as little as possible the natural 
breeding and feeding grounds of aquatic wild fowl and other desir- 
able animal life without sacrificing the success of the mosquito- 
control project. Specialists in soil conservation have also called 
attention to the adverse effects of the drainage of natural upland 
storage basins, the cleaning of stream channels, and the “brushing” 
of stream banks, all of which increase the rapidity of run-off of flood- 
water with consequent erosion that may cause serious damage to agri- 
cultural lands. Such erosion is said to cause frequently a gradual 
widening of the flood plain and silting-up of downstream areas, which 
may create mosquito-producing areas as serious as those remedied. 
Such factors as these must be considered in planning mosquito- 
control programs, and they emphasize the need of obtaining advice 
from competent specialists when making the preliminary surveys. 
The impoundage of water rather than drainage may be employed 
successfully in many cases, both in salt-water and fresh-water areas, 
since an open pond with clean margins and containing mosquito- 
destroying fish is not favorable for mosquito breeding (744). (PI. 3.) 
Where the sacrifice of wildlife habitat appears necessary to accom- 
plish effective mosquito control, a decision must be made as to the 
greater benefit to be derived. 
Sanitation, as applied to mosquito control, includes such measures 
as the elimination of artificial and other breeding places of the domes- 
tic mosquitoes. It also involves the treatment of permanent bodies 
of water by the removal of aquatic vegetation and other protective 
harborage for the larvae to make them unfavorable for mosquito 
development. 
LARVICIDES 
Various kinds of larvicides are employed where permanent methods 
of control are not feasible. Although there are many chemicals that 
will poison the larvae rather easily, the number of materials that 
are utilized in practical work is comparatively small. 
Petroleum oils have been used extensively and are effective against 
nearly all economic species. They act as contact poisons and kill 
the larvae or pupae by entering the breathing tubes. The lighter 
and more volatile oils, such as gasoline and kerosene, are the more 
toxic, whereas heavy oils are more lasting. Various mixtures of 
heavy and light oils have therefore been employed. Light distilled 
fuel oil (No. 2) is recommended for general use, since it is of fairly 
uniform quality, easily handled in large or small spraying equipment, 
and is economical in cost. Since fuel oil varies somewhat in toxicity 
according to the type of crude petroleum from which it is derived, 
preliminary tests of its effectiveness against mosquito larvae should 
be made before it is purchased in large quantities. The addition 
