October 1948 7-760
United States Lephrtment of Agriculture
Agr cultural Research Admintstration
Bureau of Entomology and Plant Quarantine
DDT AS A PHIEHATCHING TREATMENT FOR CONTROL
OF SNOW-WATER MOSQUITOES
By A. W. Lindquist, A. R. Roth, and W. W. Yates,
Division of Insects Affecting Man and Animals
DDT and other chlorinated hydrocarbon compounds have been found to
be remarkably effective against many species of mosquitoes when used on
water where larvae are present. Larvae of snow-water, or mountain,
mosquitoes can be controlled in this way, but it is exceedingly difficult
or impossible to get to the mosquito areas in the spring because of pass-
able roads. Larval development is usually complete before cars and
spray equipment can be driven over the roads and trails. The treatment
of swales or ponds in mountain areas several months before melting snow
causes mosquito eggs to hatch has been considered for several years, but
only since the advent of DDT and other residual insecticides has there
been much hope for this prehatching treatment.
Snow-water, mosquitoes create a nuisance problem to timber and road
workers, vacationists, resort owners, and others. Many recreational
areas cannot be used to full advantage because of mosquito annoyance.
The public is aware that much greater use could be made of many areas if
mosquitoes could be controlled. The results of recent tests are reported
here as a basis for setting up new control procedures where such proce-
dures are applicable.
The important species of mosquitoes in mountain areas belong to the
genus Aedes, This group is represented in the Pacific Northwest by 18 or
20 species, many of which are of minor importance. The 5 most common and
widely distributed species are Aedes communis (Deg.), A. hexodontus Dyar,
A. increpitus Dyar, A. fitchii F and Y.), and A. cinereus Meig. Aedes
mosquitoes lay their eggs in the soil and duff in swales and depressions
after the water has receded or along the shore just above the water line
in swampy areas where the water remains. The eggs hatch in the spring
when flooded by melting snow water.
The length of the larval period varies with the temperature, which
may be as low as 32 F. for extended periods. Aedes adults do not live
so long in the mountains as do those of species found at lower elevations,
but the season of mosquito annoyance may last for 1 to 3 months, because
as snow banks melt new broods are emerging. Adults are more prevalent
near the source of emergence, but can become a nuisance for considerable
distances. Their flight range varies in different localities being in-
fluenced by such factors as air currents, velocity of prevailing winds,
Many experiments have been conducted in the mountain areas of
Washington and Oregon to determine the value of using the new insecticides
as prehatching treatments on mosquito-breeding areas in the early fall
months when roads are passable and conditions are favorable for work
(Roth et al. 1). In September and October known amounts of insecticide
were applied in various formulations and by different methods. The
following May and June, when the mosquito eggs were hatching, these areas
were examined to determine the effectiveness of the treatments.
Oil solutions, water emulsions, wettable powders, and dusts of DDT
were found to be about equally effective. Oil solutions and emulsions
were applied with compressed-air sprayers. Wettable powders and dusts
were broadcast by hand over the plots. This is the easiest way to apply
dusts or wettable powders over the swales. Good coverage of the area is
desirable, but it is not so essential as when minimum dosages are being
applied in regular larvicidal applications.
Most of the experimental work was done with DDT, and it is suggested
that this compound be utilized in control. There is evidence, however,
that TDE, chlordane, chlorinated camphene, and the methoxy analog of DDT
are also effective (Roth et al. 1) and may be substituted whore price and
availability dictate a change.
DDT applied at the rate of 0.5 to 1 pound per acre prevented mosquito
development in all the experiments, and in a few instances a dosage of 2
pounds per acre was effective for 2 years. The suggested dosage is 1
pound of active ingredient per acre. This dosage would require 2 pounds
of a 50-percent wettable powder, 10 quarts of a 5-percent oil solution,
or 10 pounds of a 10-percent dust.
It is, of course, obvious that treatment be applied to known breed-
ing dreas. Many of the mosLiuito-breeding swales are known to Forest
Service workers and others. However, it may be necessary to survey an
area in the spring to determine the exact locations of the 3- -ales in which
mos'rito larvae are present. Many of the swales are less than a half acre
in size, whereas some may cover as miaqy as 100 acres. In meazurine the
swale care should be exercised in deter-nining the high-water mark.
Frequently the size of an area is underestimated and underdosage results.
DDT should not be sprayed on streams or ponds cont4iniig fish.
Fortunately, nearly all swales are dry during the summa-r, and even when
snow waters are present in the spring, fish are not frequently found.
There is practically no danger to wildlife, since the swales are usually
small and scattered, and the recommended treatment is soon covered with
snow and ice for several months of the year.
(1) Roth, A. R., Yates, W. W., and Lindquist, A. W.
1947. Preliminary studies of larvicides on snow-water mosquitoes.
Mosquito News 7(4): 154-156.
UNIVERSITY OF FLORIDA
3 1262 09239I I 1936I
3 1262 09239 1936