PARIS GREEN (ACETO ARSENITE OF COPPER) AND 
OTHER STOMACH POISONS AS LARVICIDES 
AGAINST MOSQUITO LARVAE 
By M. A. BARBER 
U. S. PUBLIC HEALTH SERVICE, MALARIA INVESTIGATIONS, MEMPHIS, TENN. 
Larvicides in powder form were first em¬ 
ployed by Tbibault (1918), who began with 
powdered pyrethrum which he found gave 
excellent results. Later he obtained “very 
good results” against both anopheles and 
culicines with various finely ground grasses 
and weeds, and he believed that the action 
of his powders was purely mechanical. We 
repeated his experiments without much suc¬ 
cess with any vegetable powder except 
pyrethrum. 
Roubaud (1920) experimented success¬ 
fully with trioxymethylene (paraformalde¬ 
hyde) against anopheles. He was the first, 
I believe, to recognize that such powders 
are effective through ingestion by the 
larvae. Barber and Hayne (1921) intro¬ 
duced arsenicals, among them Paris green, 
into this sort of work. 
The efficacy of larvicides in powder form 
against anopheles depends on two things: 
the toxicity of the poisons in the intestinal 
tract of the larvae, and the position of the 
particles of poison on the surface tension 
layer of the water of the breeding place 
within reach of the surface feeding larvae. 
The term “stomach poisons” is a good one 
with the understanding that the poisons 
may be effective in other parts of the gut. 
It is possible that the same larvicide may act 
both as a stomach and a respiratory poison. 
Chemical and Other Properties of 
Paris Green 
Paris green, a copper aceto arsenite, is a 
double salt of copper metaarsenite and cop¬ 
per acetate. In the pure state it contains 
the equivalent of 58.62 per cent of arsenious 
oxide. Under the United States Federal 
Insecticide Act of 1910, the name Paris 
green is restricted to products containing a 
minimum of 50 per cent of arsenic calcu¬ 
lated as oxide. One should be sure that 
the Paris green to be used as a larvicide 
contains at least that percentage. 
Paris green is soluble in acids and am¬ 
monia, but in the pure state is practically 
insoluble in water. In the digestive tract 
of the larva it is presumably more soluble 
than in pure water. The solubility in water 
of ordinary commercial products of Paris 
green depends on the amount of free arseni¬ 
ous oxide in them. Such products contain 
about 1 to 3 per cent of free arsenious oxide 
and average about 1.4 per cent. U. S. Fed¬ 
eral law prohibits interstate commerce in 
Paris green containing more than 3.5 per 
cent. 
Paris green, then, is especially suitable 
as a larvicide because of its high toxicity 
within the gut of the larva and its low 
solubility in the water of the breeding place. 
Again, it is easily spread and penetrates 
reeds or grass covering the surface of the 
water. It is easily transported and is rela¬ 
tively cheap. 
It has the disadvantage of failing to af¬ 
fect mosquito eggs or pupae, so that it must 
be applied at shorter intervals than oils. 
Small larvae, however, are poisoned as soon 
as they begin to eat, provided the Paris 
green used contains some fine dust, as is 
usually the case. It is comparatively less 
efficient against culicines or other larvae 
not surface-feeding (see below under the 
topic “Paris green and culicines”). 
Dilution with Dust 
When spread in powder form, Paris 
green is usually diluted with some inert 
