246 Annals Entomological Society of America [Vol. VIII, 
time being the numbers of mosquitos flying over this section. 
However, observations made tend to indicate that the path 
of flight was changed since the area was burned over, as if to 
avoid the barren waste. Mosquitos harboring in the brush 
were killed when this vegetation was burned, but these mos- 
quitos were only a very small fraction of the entire horde and 
\\ 
\ 
< 
\\5 \ \ 
on ~\ \s 
— * 50 
7 O\EN =! 
~ \ avn \ 6s 
2 \A 
ae \aU 
eT 
= oa 
GATUN LAKE 
hence their destruction amounted to very little. Ditch “A” 
(see map) was finished toward the end of January, and the 
swift current of water through it made an ideal habitat for 
the sand flies which during February became very numerous. 
Ditch ‘‘B,’’ south-west of ‘‘A,’’ was completed early in Feb- 
ruary. On the 18th of February, a dredge began to pour silt 
into the marsh, at a point about 4,000 feet to the north of 
ditch ‘“A.’’ On February 27th, the outlet of this discharge 
