BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 101 
CONTROL INVESTIGATIONS 
TESTING INSECTICIDES 
During the year a new method for dispersing insecticides as aerosols, 
or in the form of smoke, was developed, which seemed to increase the 
effectiveness of various insecticides when dispersed in the air. The 
method consists in spraying liquid insecticides or solutions of insecti- 
cides on a hot surface (375° C.) so that the material is dispersed as 
a smoke in the air. Although still in the experimental stage, the 
method may prove to be a cheap and efficient way of controlling insects 
in closed spaces, such as army barracks. Rotenone-bearing insecticides 
applied in this way have proved effective against houseflies and mos- 
quitoes, and an orthodichlorobenzene-naphthalene mixture is effective 
against cockroaches, bedbugs, houseflies. and mosquitoes, and is very 
inexpensive. 
The cooperative work with the Division of Drug and Related Plants 
of the Bureau of Plant Industry on American-grown pyrethrum and 
rotenone-bearing plants was continued. Approximately 3.000 tests 
were made on 640 plant materials by the biological-assay method. The 
results indicate that American sources of these insecticides are prom- 
ising, a finding that will be significant in case foreign sources are 
cut off. 
The work on synthetic organic compounds has been directed largely 
toward extending tests of materials that had previously shown tox- 
icity to insects. Field-laboratory methods were developed for deter- 
mining the length of time the insecticide would remain effective on 
foliage under natural conditions, the plants being sprayed in the 
field and the leaves removed to the laboratory at various intervals 
for tests on the insecticide. In these tests one material retained its 
toxicity for about 10 days under practical conditions and three others 
showed promise. They produced little if any injury to the foliage 
of various truck crops to which they were applied. Another, phthal- 
onitrile, was toxic to eight species of leaf -feeding larvae, but lost 
its toxicity after 4 to 6 days on the foliage, the residue apparently 
being lost by volatilization. Consequently, there should be no objec- 
tion to the spray residue from this compound. Another material 
that had shown toxicity to leaf-feeding insects was also toxic to 
houseflies. 
A fumigant was found that in laboratory tests was at least equal 
to carbon disulfide in toxicity to stored-grain pests. Approximately 
5,000 tests were made, including the tests with the 126 compounds 
that were available for the first time. Of these new compounds 
about 12 showed possibilities of being useful insecticides. 
Laboratory tests showed that insecticides ground very fine, to an 
average particle diameter of 1.1 microns, caused higher mortality in 
Mexican bean beetles and permitted less feeding than the coarser 
samples of the same insecticide with particles 12 to 22 microns in 
diameter. 
FUMIGATION INVESTIGATIONS 
Investigations on the fumigation of nursery stock with methyl 
bromide for the immature stages of the Japanese beetle were con- 
tinued. It was shown that complete mortality could be obtained 
in soil masses as large as 12 inches in least diameter, and dosages 
and exposures were worked out for the commercial application^ 
