20 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 
of about 1 percent of castor oil or crude cresol has been recommended 
as a means of increasing the spreading power of the oil. 
Paris green is highly toxic as a stomach poison to mosquito 
larvae (5) and is now used extensively in the control of anopheline 
mosquitoes. It is effective in very small quantities and, since these 
iarvae feed at the surface of the water, the material can be applied 
economically as a dust in admixture with an inert diluent. Experl- 
ments by King and McNeel (103) have shown that this arsenical 
also is effective against the salt-marsh species and some of the other 
subsurface-feeding larvae, including Psorophora confinnis and Culex 
guinquefasciatus, when mixed with water and sprayed on the breed- 
ing places from a sprinking can. After several years’ experience in 
the control of domestic mosquitoes in Miami, Fla., Stutz* has con- 
cluded that paris green has a valuable place in the control of these 
species, being especially effective in unused toilet bowls and old tires, 
where it can be applied in excess and prevents breeding for longer 
periods than do other larvicides. A heavy dusting of large piles of 
used tires with undiluted paris green has been highly effective. It 
is also sprinkled into dry containers that will become filled with water 
at the next rain. 
Soap emulsions of pyrethrum, extract in kerosene oil have been 
developed by workers in New Jersey (67) and are employed suc- 
cessfully as mosquito larvicides. The cost is low, and the use of 
pyrethrum greatly reduces the quantity of oil required, which is a 
desirable feature under some conditions. Two formulas for the 
preparation of the emulsion, adapted from those given by Ginsburg 
(60), are as follows: 
Against fresh-water larvae—Two gallons of kerosene containing pyrethrum 
extract equivalent to 1 pound of pyrethrum flowers per gallon, and 1 gallon of 
water containing 8 to 10 ounces of liquid 40-percent potash soap. 
Against salt-water or fresh-water larvae—Two gallons of kerosene containing 
pyrethrum extract as above plus 2 ounces of defoamer, and 1 gallon of water 
containing 2 ounces of sodium lauryl sulfate. 
With both formulas the emulsifying agent is dissolved in the water 
and the oil containing pyrethrum extract slowly added with constant 
mixing (in a container with agitators or by pumping the mixture 
vigorously back into itself) until a creamy emulsion is obtained. 
After the foam has settled, 1 part of this stock solution is mixed 
with 9 parts of water, and the diluted mixture is sprayed onto the 
breeding places at the rate of about 50 gallons per acre. The stock 
emulsion can be prepared in large quantities by mixing in the tank 
of a power sprayer. The pyrethrum extract is usually purchased 
in a concentrated form, 20 pounds of the flowers per gallon, and 
diluted at the rate of 1 gallon of extract to 19 gallons of oil (6.4 fluid 
ounces per gallon of mixture). 
The sodium lauryl sulfate and the defoamer can be obtained on 
the market, or the defoamer can be prepared by mixing equal parts 
of fuel oil and wool grease. The prepared stock emulsion can also 
be purchased. Other commercial wetting agents that may be em- 
ployed as emulsifiers are available. 
39rurz, Prep H. SIxtTH ANNUAL REPORT OF THE DADE COUNTY, FLORIDA, ANTI-MOSQUITO 
DISTRICT COVERING ACTIVITIES FOR 1940. 17 pp. [Processed.] 
