382 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
other deposits that have been treated with oil may be similarly ex¬ 
plained. We have known of one case in which there were even second- 
stage Stegomyia larvae in a tambour of water on which a film of oil 
had been placed by an agent twenty-four hours before. 
In a second experiment five bottles were set up and supplied with 
water, larvae, and kerosene, which was removed after periods of five, 
ten, fifteen, or thirty minutes. In the bottles from which the oil was 
removed after five minutes a large proportion of larvae survived, but in 
all the other bottles the larvae were killed. It may be assumed therefore 
that the time of exposure necessary to kill all but a very small number of 
larvae lies between five and ten minutes. (See Table 2.) 
In a third test the larvae were exposed to the oil for one, two, three, 
and four minutes respectively, but it was found that too high a per¬ 
centage of larvae survived these shorter contacts. (See Table 3.) 
The larvae destroyed in these experiments were killed either by the 
toxic action of petroleum or by the exclusion of their supply of oxygen. 
In the latter case death may have been due to long exposure to the 
kerosene or, where the larvae were subjected for but a short time to 
the action of the kerosene, death may have resulted from the occlusion 
of the breathing syphon with a globule of oil. It is reasonable to suppose, 
however, that the larvae could free themselves of an impeding globule 
of kerosene by the use of their mouth brushes. Certainly the exclusion 
of their supply of oxygen for five or ten minutes would not kill them, 
for it has been shown that Aedes calopus larvae will live for from three 
and one-half to thirty-six hours when deprived of oxygen by mechanical 
means only. The death, then, of those larvae exposed but for a few 
minutes to the film of kerosene can be accounted for only on the suppo¬ 
sition that the kerosene acted as a selective toxin. 
Not all oils show this toxic property, as was discovered by a further 
experiment. In this test we used large bottles nearly full of water, 
adding only ten larvae to each bottle to avoid the complication of 
suffocation through overcrowding. In the first three bottles we placed 
a thick layer of gasoline; in the next three, different grades of kerosene; 
in the next three salad oil, and from the last three we excluded air by 
mechanical means. At the end of two hours all the larvae were dead 
under the gasoline and kerosene, but under the salad oil twenty-four 
were still living, while twenty-eight were living in the bottles from 
which the air had been excluded by mechanical measures. At the end 
of seven hours there were eight larvae living under the salad oil and nine 
