356 
MALARIA 
Filling 
Going hand in hand with drainage as an 
anopheles control method is that of filling, 
thereby eliminating once for all some breed¬ 
ing areas. It has the advantage of not dis¬ 
turbing the ground water table. This is a 
method always to be considered but oft- 
times overlooked. 
Use of Minnows 
In the early days of mosquito control it 
was noted that top minnows (Gambusia 
affinis or holbrooki), abundant in rivers, 
streams and ponds, consumed large num¬ 
bers of mosquito larvae. Stocking of im¬ 
pounded lakes, ponds, and almost all types 
of water deposits with these fish was her¬ 
alded as an effective naturalistic method 
available for the elimination of mosquito 
larvae. To be effective against larvae the 
water must be sufficiently free of vegeta¬ 
tion to permit the fish considerable freedom 
of movement, because mosquito larvae are 
admirably adapted for camouflage against 
twigs, plant stems, etc. When water has 
been rendered clear and unobstructed by 
removal of vegetation and floatage so that 
minnows can be effective, this very condi¬ 
tion in itself has minimized or prevented 
mosquito breeding. 
Minnows, therefore, should not be relied 
upon as a prime measure against anoph- 
eline production in this region. Bather 
their use constitutes an auxiliary or sec¬ 
ondary method which is of some value. 
Minnows when propagated in ponds, lakes 
and large reservoirs located at a distance 
from habitations often reduce breeding of 
mosquitoes in these deposits sufficiently to 
minimize their importance as producing 
areas. 
Larvicides 
The value of oil (kerosene) against mos¬ 
quito larvae was demonstrated by L. 0. 
Howard in 1892. This was probably the 
first use of a larvicide against mosquitoes 
and the application of various larvicides to 
the surface of water still remains one of 
the most effective methods of controlling 
malaria. 
In order to insure economy and effective¬ 
ness larvicides should be applied under 
careful entomological supervision. Their 
application should be limited to places 
where actual breeding is known to occur. 
A check for the presence of adult anopheles 
often gives valuable clues to hidden breed¬ 
ing places which can usually be controlled 
with larvicides, pending the application of 
more permanent methods. 
Screening 
The screening of rural houses, while not 
a measure directed against the production 
of anopheles, is a measure directed at the 
control of the adult insects, in so far as 
their association with man is concerned. 
Its field of usefulness is in highly endemic 
rural areas where conditions are such that 
other methods of malaria control are not 
practicable. The deplorable condition of 
the majority of rural farm houses makes it 
necessary to mosquito-proof the walls, roof 
and floors, in addition to providing screens 
if anophelines are to be kept out. As dif¬ 
ficult as an effective screening program 
may at first sight appear to be, it has been 
found economically feasible in many rural 
areas. The biting period of anopheline 
mosquitoes commences at twilight, hence 
the protection offered by a screened house 
is doubtless greater than that of bed nets 
not ordinarily utilized until some time 
after dark. 
Around some impounded water projects 
where mosquito control failed, it was neces¬ 
sary to screen and mosquito-proof the 
houses within one mile of the shore line. 
Following the Mississippi Kiver flood in 
1927 much rural screening was done in the 
adjacent territory and statistics are avail¬ 
able tending to demonstrate its anti-ma¬ 
larial value. However, the data are not 
conclusive and it must be remembered the 
responsibility for maintenance rests upon 
the occupant. The Tennessee Valley Au¬ 
thority has found the screening and mos¬ 
quito-proofing of rural houses in one special 
area an effective malarial control measure 
where the prevention of anopheline breed¬ 
ing was impossible. 
