Report on Mosquitoes Collected in St. Louis County During 1942 43 
Relation to Disease 
Anopheles comprise 26.0 per cent of the total niosquitoes. The 
situation is somewhat comparable to that recorded by Feemster 
and Getting (1941) for Massachusetts where this genus made up 
11.9 per cent of a total of over a quarter of a million specimens 
identified in the 1939 mosquito survey of that state. Yet there 
were only eleven cases of malaria probably contracted ui Massa- 
chusetts in the ten year period 1930-1939 (Getting et al., 1940). 
In St. Louis County the disease is more prevalent than this, 
though exact figures are difficult to obtain. Malaria is endemic 
in the southeast corner of Missouri and many of the cases re- 
corded in St. Louis are doubtless contracted during visits away 
from the city and county. Since about sixty breeding places of 
Anopheles quadrimaculatus were found and adults were collected 
in abundance over the whole county the scarcity of the vector 
hardly seems the cause of the comparative scarcity of the disease. 
Anopheles quadrimaculatus probably occurs in sufficient numbers 
to account for the small amount of malaria contracted m the 
county. The actual abundance necessary for the continued occur- 
rence of the disease will vary with a number of factors but the 
statement of Johnson (1941) that "A. quadrimaculatus ^ reduction 
to the point where only occasional adults are found in suitable 
diurnal shelter, is effective" in reducing malaria, is significant in 
this case. The greatest number of this species taken in one day s 
collecting in barns, culverts and such favorable locations was 410 
(August 4). Though A. piinctipennis is as abundant and bites 
with great frequency and will transmit the various species of 
Plasmodium in the laboratory, it is not considered important as 
a vector in nature (Darling, 1926). 
sibl 
In regard to the bearing of the present findings on the pos- 
e vector of St. Louis encephalitis, if the disease is mosquito- 
borne, it seems likely that the vector is probably Cnlcx pipiens or 
possibly other species of this genus. The experimental work indi- 
cates a species of Culex rather than Aedes, but equine ence- 
phomyelitis is most probably transmitted principally by Aedes 
(Feemster and Getting, 1941). Of the six species of this genus 
