380 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
NOTES ON THE LENGTH OF TIME AEDES CALOPUS 
(STEGOMYIA) LARVAE SHOULD BE EXPOSED TO A FILM 
OF KEROSENE 
By M. E. Connor, M.D. and W. M. Monroe, M.D. 
International Health Board 
Abstract 
A ten-minute exposure to a film of kerosene is sufficient to cause the death of all 
but a very small percentage of Aedes calopus larvae, and for this reason washer¬ 
women may after ten minutes skim off the film of kerosene from their water con¬ 
tainers and use any portion of the water underneath. 
It would also seem that the petroleum acts not only to exclude the larvae’s supply 
of oxygen but also as a toxin, and in this capacity is responsible for most of the 
larval death rate, as its toxic action is more rapid than its mechanical effect. 
The question as to the length of time that the Aedes calopus larvae 
live after the oxygen of the air has been denied them came up for study 
in the field work of the staff engaged in the control of yellow fever in 
Tampico, Mexico. 
Throughout the gulf coast region of Mexico the tap and well water 
are so heavily charged with calcium salts that the washerwomen find it 
necessary to mix wood ashes with the raw water in order to counteract 
its hard quality. The softened water, which is callpd lejia, is alkaline 
in reaction and appears to be especially attractive to the Aedes calopus. 
Receptacles in which lejia is stored can be made proof against mosquitoes 
■only by covering the surface of the water with refined petroleum. These 
containers cannot, like the tanks, be supplied with perfectly fitting covers, 
nor can they be stocked with fish like the barrels containing fresh water, 
for fish will not live in lejia. Moreover, the container cannot be emptied 
and left inverted, since lejia is important as a means of livlihood to a 
large number of people. It was the practice of our inspectors, therefore, 
to place a good film of oil on the surface of the lejia in which breeding 
was known to occur, and this measure appeared to be successful in 
killing in a reasonable time the greater number of larvae in the containers. 
Frequently, however, in the course of re-inspection of mosquito con¬ 
trol work, a single larva would be found in many of the lejia containers 
that had been treated to a coating of kerosene. The suspicion arose 
that either the inspectors had not properly oiled the containers or that 
the larvae were developing resistance to the oil. When one district 
inspector reported that he had detected a woman skimming from a 
lejia container a film of oil placed there only a few minutes before, the 
mystery of the single larva was partly explained, and there was opened 
up the interesting question as to the minimum time that a good film of 
oil must remain on lejia to be effective. 
The time required to kill larvae through depriving them of oxygen 
