302 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. H 
were experimenting. If there were none other than the “ mechanical 
barrier” action on the part of the oils, all of these larvae should have 
died at the same time. On the contrary, however, we find a great 
difference in time, ranging from 45 minutes under the kerosene to 3 
hours under the crude oil. 
Somewhat along this line McFie gives the account of an experiment 
in cutaneous respiration wherein he kept totally submerged larvae of 
A. calopus alive for over twenty days, the only necessary factor seem¬ 
ing to be that the water should be running slowly. The evidence, 
therefore, seems quite sufficient for discarding the suffocation theory. 
(3) Poisoning through Aqueous Solution 
The idea that some portion of the oil may be dissolved or suspended 
to a slight extent in the water in which the larvae are living and thus 
produce the toxic effects has been suggested. 
In our experiments we proceeded somewhat as follows: A quantity 
of boiled water was placed in a large funnel, covered with a deep layer 
of kerosene and allowed to stand for four hours. At the same time, 
an equal volume of the same water was tightly sealed in a glass jar. 
At the end of this period the water that had previously been treated 
with kerosene was drawn off from the bottom of the funnel without 
disturbing the oil film and placed in equal amounts in six vials. Equal 
volumes of water were drawn from the sealed bottle of untreated water 
and placed in corresponding vials. One larva was introduced into each 
of the twelve tubes and the water was then sealed with hot paraffin. 
The average length of time during which the larvae survived in the 
normal water was 25J hours and the corresponding period for those in 
the kerosene treated water was 25| hours showing rather definitely 
that the solubility of kerosene in water is not a toxic factor in the 
killing of larvae by its application to the medium in which they live. 
Quoting again from McFie in an experiment where he used Man- 
eonioides africanus, a type particularly adapted for the purpose through 
its faculty for cutaneous respiration and its subsequent habit of re¬ 
maining on the bottom of the container we find “ a larva was kept in a 
jar of water to the surface of which crude kerosene . . . had been 
added. For three days it appeared to be unaffected and on the fourth 
day it pupated” thus showing no ill effects of the oil on the surface. 
From these accounts it may be concluded that the efficiency of the 
kerosene as a larvicide is independent of its solubility in the water. 
(4) Blocking of the Tubes 
The effectual suffocation of the larva through the entrance of the oil 
into their siphons and the actual physical blocking of the tubes by its 
presence has been suggested by Ross (1902). 
