LU'RKAl" OF KNTOMOLOGY AND PLANT QUARANTINE 105 
surface such as an electric hot plate. When tested against the housefly 
the smoke from burning derris powder was more than 10 times as 
toxic as that from pyrethrum burned in the same way. 
Various colorimetric methods that have been proposed for evaluat- 
ing rotenone products were compared, and a method was developed 
for determining deguelin in derris and cube. Heretofore no method 
of estimating this valuable insecticide was known. One extraction 
with water removed from 24 to 41 percent of the active material from 
derris, cube, and timbo and successive extractions removed more. 
When preserved against fermentation, these suspensions of the active 
principles are stable. The only domestic source of rotenone is T ephro- 
sia virginiana (L.) Pers., known as devil's-shoestrings. Because of its 
potential importance as an agricultural crop and as a substitute for the 
foreign-produced derris and cube, the nature of its active ingredients 
was studied very thoroughly. Deguelin was found in it for the first 
time, and several other definite crystalline compounds were isolated 
although not definitely identified. 
The toxicity to the housefly of several compounds of the rotenone 
series was determined, in cooperation with the Division of Control 
Investigations. The following concentrations dissolved in kerosene- 
cyclohexanone (milligrams per cubic centimeter) were found to be 
necessary to give 50-percent mortality : Rotenone 0.30, levodihydro- 
rotenone 0.38, levodihydrodeguelin 0.51, levo-^-dihydrorotenone 0.52, 
ievodeguelin concentrate 0.57, racemic deguelin 0.59, and racemic di- 
hydrodeguelin 0.83. When dissolved in acetone the two racemic com- 
pounds were much less toxic than when dissolved in kerosene-cyclo- 
hexanone, but the other compounds were about equally toxic in the two 
solvent.-. 
Because of the importance that these rotenone plants have attained, 
efforts were continued to find other plant materials with insecticidal 
value. Methods were developed for concentrating the active principle 
of the Amur cork tree (Phellodendron amurense Rupr.), and its 
chemical nature is being studied. Several other plants reputed to 
have insecticidal effect were examined in a preliminary fashion. They 
included thunder-god vine (Tripte? i ygiam wilfordii Hook, f.), Ken- 
tucky coffeetree {Gymnocladus dioica (L.) Koch), sweet basil (Oci- 
mu?n basilicum L.), creosotdbush (Larrea dwaricata Cav.). and Stil- 
lingici dentata (Torr.) Britt. and Rusby. Only the thunder-god vine 
yielded results sufficiently encouraging to warrant more work. 
The United States imports annually from 15 to 20 million pounds 
of pyrethrum flowers, largely from Japan. The two active princi- 
ples, pyrethrin I and pyrethrin II, find wide use in household fly 
sprays, cattle sprays, and dust insecticides for application to celery, 
cabbage, cranberry, and many other crops. Pyrethrum is a valuable 
insecticide because it leaves no poisonous residue on foodstuffs and 
because it acts quickly. No synthetic material has been found that ri- 
vals pyrethrum in speed of action. A study of the structure of pyreth- 
rins I and II has been prosecuted in the hope that it would be possi- 
ble to synthesize compounds of less complexity which, because they 
retained part of the structure of the pyrethrins, also shared their 
remarkable insecticidal activity. This work has definitely proved thai 
there is an allene structure in both pyrethrins, and with this point es- 
tablished it will be possible to proceed to the synthesis of analogous 
