28 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 
sod dam or wooden spill gate may be inserted, somewhat lower 
than the marsh level, to prevent complete drainage of the pond and 
to permit the inflow of high tides. Deepening of the shallower 
ponds may be necessary to obtain surface drainage on the neighbor- 
ing marsh and should greatly increase their value and permanence. 
Sump drainage may be employed to decrease mosquito breeding 
in small, enclosed areas where drainage is difficult, or in areas that 
are of special value from a conservation point of view. By this 
method ditches are dug so that the water is concentrated in the 
lowest portion of the marsh, where, if no pond or pool exists, one is 
excavated to serve aS a reservoir for maintaining predacious min- 
nows and insect enemies of mosquito larvae. In successful operation 
light floodings of adjacent breeding areas are drained into the sump 
by the ditches, and when the whole marsh becomes flooded the ditches 
facilitate access of the predators to all parts of the area. Successful 
use of this method was reported by Stutz * in Broward County, Fla., 
for controlling breeding in low subdivision squares where adequate 
drainage was impractical. 
Another problem arises in connection with the lowering of the 
water table, which results sometimes in an undesirable change in 
plant species and sometimes in a subsidence of the marsh level. As 
such changes vary greatly with different soil and tidal conditions, a 
thorough study of such factors should be included in the original 
surveys. Where the soil texture indicates little water-holding capac- 
ity, excessive lowering of the water table may be avoided in some 
cases by the use of very shallow ditches. 
Larvicides are employed in salt-marsh mosquito control for the 
treatment of areas that are not taken care of by the ditching system. 
Fuel oils are used extensively for this purpose and are usually ap- 
plied with a knapsack sprayer. Since the heavier, less volatile oils 
are harmful to wild birds, fish, and other aquatic animals, it is 
recommended that only relatively volatile oils, such as No. 2 fuel 
oil, be used in treating mosquito-breeding areas where wildlife is 
likely to be affected. The pyrethrum-extract emulsion as described 
on p. 20 has been recommended where wildlife is concerned. Paris 
green has given promising results against salt-marsh Aedes larvae, 
and is more economical than oil in labor, material, and transportation 
costs, in addition to being much less disagreeable to handle. It is 
mixed with water and sprayed over the breeding area with a sprink- 
ling can having a capacity of 3 or 4 gallons. Two gallons of water 
will cover about 1,250 square feet and should contain about 1 ounce 
of paris green for an application at the rate of 2 pounds per acre. 
For use in shallow water and with even distribution the amount of 
paris green can be reduced by at least one-half. The water used is 
dipped from the breeding place as needed. It should be strained, 
if necessary, to prevent clogging of the sprinkler head with trash. 
NOTES ON THE GENERA AND SPECIES 
The genera and species are discussed in the following pages. As 
few mosquitoes are known by common names, the scientific name will 
3 STUTz, FRED H. SIxTH ANNUAL REPORT OF THE BROWARD COUNTY, FLORIDA, ANTI- 
MOSQUITO DISTRICT COVERING ACTIVITIES FOR 1940. 9 pp. [Mimeographed. ] 
