354 
MALARIA 
and the consequent restriction of malaria 
to rural districts. 
The rural areas adjacent to the flood 
plains of rivers are, on the contrary, es¬ 
sentially agricultural and tenant farming 
is often practiced. Modern improvements 
are not available, screens are not normally 
used, housing is poor, wages are low, and 
the tenant farmers live largely from hand 
to mouth. In the southeastern states where 
anophelines are abundant, malaria still re¬ 
mains a serious economic burden to this 
class. 
As serious as may appear to be the eco¬ 
nomic plight of sections of the United States 
where malaria is seriously prevalent, it is 
my belief that they could show a profit by 
controlling malaria, even if they chose the 
most expensive method. Fisher (1920) 
has investigated the question of how much 
a community can afford to pay for malaria 
control. Working from the angle of the 
probable return on the investment, he de¬ 
duces a formula to indicate what return 
might be expected from an investment in 
control measures. 
Anopheles control measures are some¬ 
times classed as permanent or temporary; 
mechanical or chemical; natural or artifi¬ 
cial; naturalistic, etc. In this paper they 
will be considered under the general items 
of Water Level Fluctuation; Clearing; 
Drainage; Filling; Use of Minnows; Larvi- 
cides; Screening; Naturalistic, and Mis¬ 
cellaneous. 
Water Level Fluctuation 
The shallow vegetation-covered areas of 
impounded waters present ideal conditions 
for the propagation of A. quadrimaculatus 
because, under such conditions, an abun¬ 
dant food supply exists and protection is 
afforded from natural enemies. Water 
level fluctuation should be used as a mos¬ 
quito control method wherever the level 
can be suitably regulated for it has been 
demonstrated that without its aid other 
methods are unable to suppress breeding. 
Fundamentally a suitable fluctuation 
schedule commences with a high water level 
at the beginning of the anopheles breeding 
season, followed by a rapid lowering of the 
level a foot more or less each 10 days until 
the end of the breeding season. Such a 
schedule strands floatage and assures a rea¬ 
sonably vegetation-free edge. By thus cre¬ 
ating clean banks and open water condi¬ 
tions, anopheline production is minimized. 
This ideal schedule cannot always be put 
into effect. 
Water level fluctuation is rendered 
vastly more effective as a mosquito control 
measure by a preliminary clearing of vege¬ 
tation and floatable material in the pro¬ 
posed basin prior to impounding, and, in¬ 
deed, most states in the malarious belt re¬ 
quire such clearing before a permit to im¬ 
pound will be granted. After impound- 
age, it often becomes necessary to employ 
secondary measures of control, such as lar- 
vicide application, on parts of the shore 
line not adequately controlled by fluctua¬ 
tion alone. 
Anopheles production may also be cur¬ 
tailed in smaller ponds and lakes by a 
downward fluctuation of water level dur¬ 
ing the mosquito breeding season with or 
without vegetation clearing, although pro¬ 
vision for fluctuation was not originally 
made. Natural fluctuation caused by dry¬ 
ing or evaporation during the anopheles 
producing season is often responsible for a 
great reduction in anopheles propagation 
in many smaller water deposits. 
Clearing 
In the larval form, mosquitoes find pro¬ 
tection from natural enemies under dense 
aquatic vegetation and among floatage. 
Both favor anopheles production by slow¬ 
ing down the current, creating still, ripple¬ 
less water, affording direct larval protec¬ 
tion, providing food, and hindering the 
proper distribution of larvicides. Low 
vegetation having horizontal leaflets, as cer¬ 
tain grasses and weeds, are ideal for larvae 
protection as contrasted with the upright, 
tall, straight emergent types, as rushes and 
bushes. 
Clearing, or the removal of this protec¬ 
tive vegetation and floatage, is an impor¬ 
tant part of any program directed against 
