Report on Mosquitoes Collected in St. Louis County During igp 33 
2) Geographical Distribution. St. Louis County, com- 
prising an area of approximately 500 square milfb, is situated at 
the junction of the Missouri and Mississippi rivers and is bor- 
dered on the south In part by the Meramec River. There are 
therefore many natural breeding places for mosquitoes and, 
while some species are local in distribution, all the more abun- 
dant species have been found wherever widespread collections 
have been made. Admittedly, however, collections have been 
much less extensive in the western and less populated parts of 
the County. 
3) Seasonal Distribution and Prevalence. The species 
found were distributed through the summer as shown in Table 2. 
Further work will undoubtedly extend these records considerably. 
The data from this survey are probably inadequate for a 
general discussion of seasonal prevalence because of the very 
unusual weather conditions obtaining during the summer of 1942 
as is indicated in Graph 1. 
Total collections per month are more an indication of the 
activity of collectors than of actual abundance, but a more reli- 
able indication of seasonal abundance is provided by the stand- 
a light trap. Six of these (New Jersey 
Agriculture Experiment Station Model 50) were eventually ^set 
up during the season, but only for one, that on Washmgt.^n Lm- 
versity campus, are the data sufficiently complete for critical 
analvsis. These data are plotted on Graph 2 together with rain- 
fall as registered at the Washington University weather station. 
It has been found that, of the total mosquitoes caught in 
light traps, 43.4 per cent belonged to the genus Aedes (41.4 per 
cent, Aedes vexans); 38.7 per cent to the Cidex, and 15.3 per 
cent to Anopheles. The number of trap nights on which 24 or 
more females were taken was 14 per cent. As in the report ot 
Rowe (1942) for Iowa, periods of Increased mosquito abun- 
dance follow within 10 to 20 days after heavy rain. The maxi- 
mum occurred in all St. Louis County light traps within a weeK 
of the middle of Julv, following the unusually heavy ram ot 
ardized collections from 
