Circular 21 - Insecticides and Subsidiary I.feterials 66 
The undiluted gro-ond flov;ers may be dusted 
into clothing as a repellent against fleas, 
or scattered around infested areas to control 
roaches. A good diluted dust may be prepared 
from pure fresh pov/der and from 2 to 5 parts 
of some inert carrier such as talc or diatoma- 
ceous earth. In this form it may be applied 
directly to infested animals to control fleas 
and lice or dusted behind baseboards and 
similar locations to des-croy fleas, bedbugs, 
or roaches in buildings. 
The pyrethrins are also extracted from 
the flowers with various solvents such as ace- 
tone, alcohol, ethylene dichloride or mineral 
oil, according to the purpose for which they 
are to be used. Those prepared w^ith alcohol 
and acetone are commonly used agriculturally; 
the oil sprays find application against insects 
affecting man, animals, and stored commodities. 
Such oil sprays are frequently prepared in the 
form known as 20-to-l concentrates which con- 
tain 2 grams pyrethrins per 100 cc. For many 
purposes these are diluted about 20 times with 
kerosene or other light petroleum oil to make 
sprays containing about 0.10 to 0,12 grams 
pyrethrins per 100 cc. The oil used should 
be readily volatile and leave no stain on the 
sprayed objects. A perfume is often added to 
mask the odor. 
The diluted oil -pyre thrum extract may 
be used against house flies, stable flies, 
mosquitoes, eye gnats, sand flies, chiggers, 
fleas, cockroaches, bedbugs, ticks, clothes 
moths, silverfish and ants in and around 
rrLlitary establishments . 
V/lien pyrethrum is used in livestock or 
cattle sprays to kill and repel flies, the oil 
solution must be of such a nature as not to be 
