292 
MALARIA 
the annual maintenance necessary to keep 
the channels functional. The costs are ex¬ 
ceedingly variable but can usually be an¬ 
ticipated in different terrains with a rea¬ 
sonable degree of accuracy. To a consid¬ 
erable extent, these maintenance costs may 
be reduced by paving ditch-bottoms with 
concrete, clay, brick, or masonry and by 
stabilizing the slopes of open ditches. The 
construction costs of such procedures limits 
their application to urban and suburban 
situations where, generally speaking, it is 
better practice to invest a little more money 
and install a closed, subsoil drainage sys¬ 
tem if possible. While these refinements 
in design and construction do reduce main¬ 
tenance costs, they rarely, if ever, succeed 
in eliminating it. 
Certain breeding-places, however, rep¬ 
resent interests vested in power, wild-life, 
recreational or ornamental values and can¬ 
not be destroyed. In such situations the 
only alternative to depopulation is tem¬ 
porary or semipermanent control mea¬ 
sures such as larvicidal applications, mos¬ 
quito-proofing, or medication. Good anoph- 
eline larvicidal effect may be obtained 
with either oil or Paris green. Oil has the 
advantage of being lethal to all mosquito 
larvae whereas Paris green is mainly effec¬ 
tive against anopheline larvae. The ma¬ 
terial costs of oil are about twice those of 
Paris green and the radius of application is 
somewhat less. Thus oil is more expensive 
but provides nullification of a pest problem 
as well as a health hazard. Larviciding 
should be employed either as a supplement 
to or during the development of a drainage 
program. It is rarely economical to substi¬ 
tute it for drainage. If, however, it can 
be demonstrated that the annual costs of 
ajrea-wide larviciding are less than the 
annual maintenance and amortization costs 
of drainage for the same area, the proposi¬ 
tion should be seriously considered. 
Most malarious states have regulations 
promulgated for the control of artificial 
impoundments. Such bodies of water pre¬ 
sent very special malaria problems due to 
the fact that natural fluctuation of pool 
level in response to rainfall and run-off 
does not occur as in natural ponds. Fluc¬ 
tuation is an effective anti-larval method 
and, where feasible, means for achieving it 
in artificial impoundments should be speci¬ 
fied in the malaria survey report. Clear¬ 
ing, bank-sloping, herbicidal treatment, 
marginal drainage, and larviciding may be 
necessary as supplementary measures to 
suppress anopheline production in im¬ 
pounded ponds and lakes. The cost of ma¬ 
laria control operations on revenue-pro¬ 
ducing impoundments should be borne by 
the owners. 
The use of larvicides presupposes that 
under local conditions sufficiently effective 
control of breeding can be obtained to re¬ 
duce malaria rates and enough people live 
within flight-range of the treated ponds to 
justify the costs. This is not always true. 
Using ground or boat equipment, oiling 
costs about $20 per season-acre, Paris-green 
dusting, $15; airplane dusting, if the vol¬ 
ume justifies it, is less expensive, about 
$7.50 per season-acre according to Kiker, 
Fairer and Flanary (1938). Thus it may 
be more economical to provide mosquito¬ 
proofing than larviciding in the vicinity of 
ponds where population is scanty. The 
Tennessee Valley Authority has encoun¬ 
tered situations where standard Paris-green 
airplane dusting does not kill enough 
larvae to control local malaria morbidity, 
and has, therefore,, substituted screening 
and mosquito-proofing for anti-larval mea¬ 
sures. 
An insect-proof house is part of a mini¬ 
mum standard of living and should not 
have to be promoted as a specific anti¬ 
malaria measure. Nevertheless, thousands 
of unprotected houses exist within flight- 
range of anopheline breeding-places. 
Where filling, drainage, or anti-larval mea¬ 
sures are not practicable, some of these 
houses can be screened at a reasonable frac¬ 
tion of their present value. It is in such 
situations that mosquito-proofing should 
play a part in the malaria control program. 
The effectiveness of this measure is depen¬ 
dent upon the residents’ understanding its 
purpose and that its value will be reduced 
