330 
MALARIA 
the second and third groups will be dis¬ 
cussed together. 
Normally terrestrial species of vegetation 
are of slight consequence in anopheline 
propagation. With the employment of a 
seasonal recession there is a marked ten¬ 
dency for these species to invade the zone 
of drawdown, and if a summer flood refills 
the reservoir to top elevation they provide 
excellent breeding grounds for A. quadri- 
maculatus. Furthermore, the tough ves¬ 
tiges of certain of these plants may remain 
throughout the winter and constitute a suit¬ 
able environment for mosquito breeding the 
following year. In recent years the ma¬ 
laria control program of the Tennessee 
Valley Authority has included removal of 
such terrestrial vegetation and small cop¬ 
pice in certain critical areas. Mowing 
machines and rakes have been used to re¬ 
move the growth very economically. Un¬ 
fortunately, this operation is an annual 
process. Where growth removal can be 
carried out at a cost represented in larvici- 
dal savings, it is to be urged since it has the 
added advantage of increasing efficiency. 
This operation is directed toward coppice 
and terrestrial herbaceous vegetation be¬ 
cause most aquatic species are not impeded 
by this type of cutting and in certain 
instances may even be spread. 
Wetland and aquatic species of vegeta¬ 
tion are highly important in mosquito con¬ 
trol. 1 Fundamental to all plant control 
operations is a thorough knowledge of the 
morphology, and especially the ecology, of 
each species concerned. This includes the 
distribution, habitat requirements, competi¬ 
tive ability, rate of growth, phenology, and 
means of migration of each species. Al¬ 
though the methods of control of herbaceous 
plants are still in the process of evolution, 
they include (1) removal, (2) recurrent 
cutting and (3)' herbicides. 
Removal by digging, raking, pulling, or 
by a dragline is successful only when all 
the vegetative parts are eliminated and dis- 
i The following discussion is drawn exclusively 
from the experience of Dr. W. T. Penfound and 
Mr. T. P. Hall, who have been engaged in botanical 
studies for the Tennessee Valley Authority for the 
past several summers. 
posed of properly. Recurrent cutting has 
given very encouraging results during the 
past year on Tennessee Valley Authority 
reservoirs. It appears particularly appli¬ 
cable to such species as American lotus 
(Nelumbo lutea ) and cowlily (Nympheae 
advena ). Cutting either by underwater 
saw or a mechanized underwater weed 
cutter 2 has been efficient in deeper water. 
The treatment must be repeated at intervals 
of about three weeks, cutting the leaf blades 
just below the surface of the water. The 
number of cuttings required varies with the 
depth, turbidity, etc., of the water. The cut 
portions of the plants have not been found 
to promote anopheline breeding. 
Considerable attention has been given to 
the utilization of herbicides. Sodium arse- 
nite in weak solution (3 per cent) applied 
assiduously destroys those portions of the 
plant to which it is applied. Its use is 
limited, however, since it is highly poisonous 
to livestock and to man. In addition, the 
reservoir must be lowered sufficiently to 
expose the entire plant. During the sum¬ 
mer of 1940 experimental application of 
powdered sodium arsenite (8 lb per acre) 
was made by airplane. This was attempted 
in the hope of reducing the vegetative cover 
to a point where the necessity for larvicidal 
application would be greatly diminished. 
Actually about a 75 per cent reduction in 
cover followed each application which was 
made at monthly intervals. .Where lotus 
(Nelumbo lutea) was present it was neces¬ 
sary to apply considerably in excess of 8 lb 
per acre. 
Liquid herbicides, non-poisonous to man 
or domestic animals, have been tested. Cer¬ 
tain fuel oils and phenolic compounds have 
exhibited some promise. There is undoubt¬ 
edly need for a powdered herbicide which 
may be applied by airplane and which is 
relatively non-toxic to man and his live¬ 
stock. 
Flushing (Sluicing) 
Early experimental studies in the control 
of anopheline larvae by stranding and flush¬ 
ing were carried on by Russell (1932) in 
2 Hockney type. 
