1934] Mosquito Investigations in Alaska 209 
Although no detailed study of the various natural factors 
controlling the abundance of mosquitoes was made, the fol- 
lowing observations were made which indicated that con- 
siderable numbers of mosquitoes were destroyed by preda- 
cious insects and other enemies. Larvse of Dytiscid and 
Hydrophilid beetles were abundant as well as backswim- 
mers, all of which are known to be efficient enemies of mos- 
quito larvse. The predacious larvse of three species of mos- 
quitoes (Table 1) were found in large numbers and birds 
and amphibians reputed to prey upon the larva or adult 
mosquito were present also in this region. 
It was a generally admitted fact that the mining opera- 
tions themselves have aided in abating the nuisance from 
mosquitoes.' The removal of the surface moss and muck 
and the dredging operations have reduced the extent of the 
breeding areas. The removal of brush has reduced the ex- 
tent of the natural environment preferred by the trouble- 
some adults and driven them away from the vicinity of the 
workmen. As a result of these two operations the conditions 
in certain localized areas have been improved greatly. At 
the conclusion of the investigation in 1931 specific recom- 
mendations were made relative to further improving the 
conditions near the mining operations. 
As indicated before the major portion of the breeding 
during 1931 was in the pools in the moss and the nigger- 
heads situated in the lower level portions of the valleys, 
These pools are usually covered partly or entirely with dead 
grass and moss from the previous year. The presence of 
this dead vegetation retards the evaporation of water as 
well as impedes the drainage. It was recommended that all 
the dead grass and moss around the operations be removed 
by burning during the spring of the year. This recommen- 
dation was prompted by the observation that an area of 
about one hundred acres which had been fired accidentally 
contained relatively few pools containing larvse while in the 
adjacent unburned areas larvse were abundant in the pools. 
Other recommendations included oiling and draining of 
