260 
Journal of Agricultural Research 
Vol. XXIX, No. 5 
The principal subjects of the tests 
have been the rosy apple aphid, Anu- 
r aphis roseus Baker, the green apple 
aphid, Aphis pomi DeGeer, the bean 
.aphid, Aphis rumicis Linn., the black 
chrysanthemum aphid, Anuraphis san- 
horni Gill., the black cherry aphid, 
Myzus cerasi Fab., and the aster aphid, 
Macrosiphum amhrosiae Thos. Pre¬ 
liminary tests further indicate that this 
material is toxic to insects of other 
orders as well as to Acarina. 
The physical characteristics of the 
fatty acids tested lend themselves ad¬ 
mirably to use as contact insecticides. 
The fatty acids showed unusual wetting 
and spreading powers when applied in 
the emulsion form to either insects or 
foliage, wetting readily such insects as 
the polished black aphids, the squash 
bug, and hairy caterpillars. Leaves 
having a waxy covering, such as nas¬ 
turtium and cabbage, are easily and 
evenly coated. The physiological ac¬ 
tion of the fatty acids on the insect 
•organism is as yet undetermined. 
Experiments so far conducted indi¬ 
cate that the toxicity of the fatty acids 
increases with the molecular weight, at 
least to a certain point not yet definitely 
determined. A practical amount of 
toxicity was reached with the sixth car¬ 
bon atom, the peak of toxicity appa¬ 
rently lying at or slightly above the 
C ip point. Toxicity is much greater in 
acid mixtures, the free acids killing at 
materially higher dilutions than when 
-combined as their corresponding sol¬ 
uble alkaline or neutral salts. In con¬ 
tradistinction to the action of nicotine, 
no variation in toxicity is experienced 
under varying summer temperatures 
and humidity, leading to the conclusion 
fhat the low volatility of the fatty acids 
Insures their retention in the body of 
the insect until action is complete. 
Plants show a varying susceptibility 
to burning by the acids of this chemi¬ 
cal series. The foliage of the apple 
is not affected when sprayed with 
strengths toxic to apple aphids. No 
injury to chrysanthemum plants was 
.shown by dilutions fatal to the black 
chrysanthemum aphid. On the other 
hand, the foliage of nasturtium is in¬ 
jured by the dilutions required to kill 
the bean aphid. 
Tests toward the practical applica¬ 
tion of the insecticidal properties shown 
by preliminary work with the long- 
chain fatty acids resulted in the selec¬ 
tion of a product commercially known as 
“double distilled coconut fatty acids” 
as embodying in the greatest degree the 
desirable features of those members of 
the series approximating the peak of 
practical toxicity. A typical sample 
of this product, much used industrially 
in soap manufacture and otherwise, 
was fractionated 2 with the following 
results: 
Per cent. 
A. - —Fraction mostly caprylic acid 
(small amounts caproic 
and capric)_4. 0 
B. —Fraction mostly capric acid 
(small amounts caprylic 
and lauric)_ 14. 6 
C. —Fraction mostly lauric acid 
(small amounts capric and 
myristic)_51. 1 
D. —Fraction mostly myristic 
acid (small amounts lau¬ 
ric and palmitic)__ 14. 1 
E. —Fraction mostly palmitic 
acid (small amounts my¬ 
ristic, oleic, and stearic)-- 8. 3 
F. —Fraction mostly oleic and 
stearic acids (small 
amount palmitic)_ 5. 6 
97. 7 
The fractions A to D as shown were 
individually tested for contact toxicity, 
fraction B, containing mostly capric 
acid, showing slightly greater toxicity 
than either A, C, or D. This tends to 
confirm the theory that the peak of tox¬ 
icity lies near capric acid C 9 H 19 COOH. 
The commercial product selected is 
liquid at usual summer temperatures 
(M. P. 27° C.), highly toxic even when 
greatly diluted, stable with lubricating- 
oil emulsions, readily obtainable in 
quantity, and at the time of writing is 
much lower in price than nicotine. 
Difficulties in the preparation of a 
stock solution and the retention of the 
insoluble acids in a stable emulsion 
have been met by the addition of an 
equal amount of benzol gasoline to the 
commercial fatty acids, afterwards using 
powdered glue as a colloidal stabilizer. 
The gasoline lowers the melting point 
to 5° C., thus serving to prevent solidi¬ 
fication of the acid globules in the 
emulsion through lowered tempera¬ 
tures, also facilitating even distribu¬ 
tion, while the glue greatly retards 
separation after emulsification. The 
stock emulsion 3 has been tentatively 
2 This work was done by the Insecticide Laboratory of the Bureau of Chemistry, United States 
department of Agriculture. 
3 Stock solution 
Coconut fatty acids (double 
distilled). 200 cc. 
Gasoline (benzol). 200 cc. 
Glue (granular)... 100 gm. 
Water. 525 cc. 
