22 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 
1 pound of the ground pyrethrum flowers in a gallon of kerosene for 
24 hours or longer, and then pouring off the supernatant fluid for use. 
Probably the most economical method of preparing a spray is to pur- 
chase a concentrated extract (usually sold to contain not less than 2.4 
percent of pyrethrins by weight, or about 2 gm. per 100 ml.) and 
dilute it with a light oil at the rate of 1 part of extract to 19 parts 
of oil. Water-white kerosene is generally used for this purpose to 
avoid staining of the clothing or walls. The pyrethrum spray is also 
effective temporarily as a mosquito repellent when sprayed on the 
ankles or the clothing. For application on the skin, a mixture of a 
concentrated extract with a nonirritating oil such as petrolatum or 
liquid vaseline may be used. Oil of citronella and other essential oils 
have long been used as temporary repellents. A preparation contain- 
ing diethylene glycol monobuty! ether acetate and diethylene glycol 
monoethyl ether as the active ingredients has been shown to be more 
effective than citronella (63) and is now available in a commercial 
preparation. 
The dry pyrethrum powder is sometimes burned as a fumigant for 
destroying mosquitoes in closed rooms. It is also used as a repellent 
smudge, and the writers have seen it employec with good results in 
a large screened camp into which swarms of salt-marsh mosquitoes 
gained entrance with each opening of the door. In the open room 
the fumes were not strong enough to be objectionable to the persons 
present but were sufficiently toxic to incapacitate the insects. To 
make the smudge the powder is mounded on a plate or other flat dish 
and ignited at the top with the aid of a little alcohol. One or more 
dishes may be used, depending on the size of the room. Grass or 
wood smudges provide some relief to livestock in open fields and stables 
during severe outbreaks of mosquitoes. It seems probable that the 
pyrethrum smudge would be much more effective than the wood smoke 
for use in the stables. 
Recent work in New Jersey (61, 62, 145) has shown that outdoor 
gatherings of people can be protected more or less from mosquito 
annoyance by a thorough spraying of the grounds and surrounding 
vegetation with a diluted emulsion of pyrethrum extract (similar to 
the formula given for pyrethrum larvicide). The spray is applied 
under sufficient pressure to produce a fine mist. Successful results 
were reported from tests in which areas as small as 1,000 square feet 
were sprayed, but Vannote (745) indicated that a marginal zone ap- 
proximately 100 feet wide should be treated in addition to the area to 
be protected. In experiments conducted in Florida by the present 
writers (101), effective results were not obtainable with the species 
Mansonia perturbans on areas 106 and 150 feet in diameter (0.2 and 
0.4 acre) when the ground was covered with only short vegetation, 
although marked reductions had occurred from the spraying in the 
smaller area before the grass and weeds had been cut. It was indi- 
cated that the method would not be feasible, against this species at 
least, for the protection of lawn parties or similar small gatherings. 
The beneficial effects of various plants or trees in repelling mos- 
quitoes have been reported, but apparently none of the reports have 
been substantiated when carefully investigated. (See Moznette (730) 
for one such instance.) Different plants have also been blamed for 
attracting mosquitoes to houses. Although no plants with such prop- 
