44 Transactions of the Academy of Science of St, Louis 
incriminated as vectors of the eastern strain of the equine dis- 
ease in Massachusetts, two have been found in St. Louis County.^ 
These are A. vexans and A. triseriatus. As shown above, A. 
vexans is one of the most abundant mosquitoes in St. Louis 
County, but A. triseriatus is less common in populated areas. 
The western strain of equine encephalomyelitis has been trans- 
mitted by four species of Aedes found in St. Louis County (see 
Davis, 1940). 
I 
A special search was made for Aedes aegypti, the yellow 
fever mosquito, which was recently recorded from Jefferson City, 
Missouri (Adams, 1942), but the species is not common in St. 
Louis County. A single female was taken on September 17th in 
the southeastern part of the county, and subsequently several 
more specimens of both sexes. 
t 
Summary 
A total of 15,100 mosquitoes from 981 collections made in 
St. Louis County in 1942 were examined. Of these specimens 
34.5 per cent were larvae. Thirty species, belonging to eight 
genera, were recorded, seven of them being new records for the 
county. Ctdex pipiens, possibly a vector of St. Louis ence- 
phalitis, IS the most abundant mosquito in the county and made 
up 30.2 per cent of the collections. Aedes vexans, a vector of 
equine encephalomyelitis, accounted for 23.3 per cent, and Ano- 
pheles qnadrimaculatus for 15.3 per cent. The latter species is 
probably sufficiently abundant to account for the malaria con- 
tracted in this area. 
The unusual weather conditions prevailing during the sum- 
mer of 1942 suggest that the picture of the mosquito population 
obtained during this survey may not be typical, but it will be the 
work of future surveys to substantiate this suggestion. 
