348 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Yol. 13 
ordinary naphthalene moth balls would be as good. Camphor was 
eliminated on account of its cost. One half of the ant-guards were 
given lump para-dichlorobenzene, the other half one moth ball each. 
A week later five of the moth ball guards had larvae and one of the 
para-dichlorobenzene also. It was evident that for ant-guards lump 
chemicals are not as effective. 
All ant-guards were now scrubbed out and left to dry for three hours. 
They were then filled with tap water and each of them was given two 
grams of powdered para-dichlorobenzene. A week later, no larvae 
were present. Without any cleaning out, two grams more were added 
to each guard. A week later, no larvae were present. It is believed 
this test proves the efficacy of powdered para-dichlorobenzene in con¬ 
trolling mosquito breeding in ant-guards. 
It was noted that adult yellow fever mosquitoes were very abundant 
at first, but as these tests continued, they became less so, until when a 
month later, there were very few present. It was also noted that 
insects, particularly wasps, would be found dead at the ant-guards 
that had para-dichlorobenzene, evidently killed by the chemical in the 
water. 
It may be well, at this point, to recall the experimental work of Dr. 
J. W. Scott Macfie 1 with common salt. He found that 2 per cent and 
upwards was effective, this being due to hypertonicity of the solution. 
In the case of para-dichlorobenzene, the action is due to the slow evap¬ 
oration of the chemical with the result that the heavy vapor leaving 
at the surface of the water is breathed by the larvae and is toxic to 
them. It forms a sort of blanket between the surface of the water and 
the air, thus shutting off the air supply. 
(6) The following laboratory experiment was made to find out the 
relative value of camphor, naphthalene and para-dichlorobenzene in 
both powdered and lump forms. Six jars were used, three for lump 
and three for powdered chemicals; each was given one liter of tap water 
and two grams of the insecticide. The camphor floated on the sur¬ 
face while the other two sank to the bottom, excepting for a very small 
quantity of the finely powdered portion which floated on the surface 
film. Each jar received 25 healthy calopus larvae. Three hours later 
(7:15 p. m.) the first observation was made. All larvae in the jars 
having lump chemicals were alive, but those in the camphor showed 
considerable distress. These were trying to remain as much as pos¬ 
sible below the water surface. The lump naphthalene and lump para- 
dichlorobenzene jars showed the larvae at the surface mostly, and if 
they did descend, they would not, as a rule, go clear to the bottom 
1 1914—A Note on the Action of Common Salt on the Larvae of Stegomia fasciata. 
Bui. Ento. Research, iv, pt. 4, pp. 339-344. 
