-14- 
sluggish and lacked control of their movements.. In 48 hours 
there had been a marked reduction in the numbers. At the end 
of 72 hours the reduction in the infestation' as compared with 
check pools "?ss notable, the visible' larvae also appearing 
rather inactive. In 5 days from the time of applying the der- 
ris, however, many larvae and pupae were still oresent and 
active-, and adults were emerging. The dusting reduced the 
infestation materially but not enough to compare favorably ^ith 
the effect of oil. 
Aedes vexans (Meig.) (- A^ sylvestris (Theob.)) 
See Ginsburg et al. 0-12, 113) under Culex pjpiens L., on 
page 18 . 
G-ibson ( 106 ) in 1927 reported that pondered derris root 
has lethal properties when used against culicine mosquito larvae. 
When dusted on the surface of -water containing larvae of this 
species this material, either alone or in combination with an 
inert filler, destroyed the larvae in a few hours, even w hen used 
at the r^te of only 2 or 3 pounds of derris to the acre. Gibson 
( 108 ) in 1929 reported that pools on the edge of scrubb"- wood- 
land and heavily infested ,T, ith mature larvae "ere dusted r 'ith 
derris',^ 3 rounds to the acre. After 18 hours the larvae appeared 
to be as numerous as ever, rnd a considerable proportion were 
pupating. In 48 hours most of them had pupated and oil ^as 
applied to prevent a possible general emergence. The derris used 
in 1928 was not that used in 1927, but both samples worked 
eaually well in the laboratory. 
T^inn ( 279 ) in 1927 reported on mosouito control at Ottawa, 
Ontario, Canada. The derris was dusted on the water surface at 
the rate of approximately 3 rounds per acre. The larvae died 
within, periods' ranging from 45 minutes to more than 7 hours. 
They became very feeble before death, lying motionless and 
parallel with the surface of the water, moving -"ith difficulty 
when rudely disturbed. The pupae died more slowly than the 
larvae, sometimes reouiring more than 24 hours. Near Montreal 
tests ^ere also made on a shallow pool about 200 feet souare, 
with a grass-grown bottom, and containing large numbers of larvae 
of Aedes vexans. A mixture of derris and French chalk (l to 4) 
was dusted just before sundown on the surface of the wpter by 
means of a small hand dust gun, et the rate of 1.5 rounds of 
derris to the acre. The material settled '-ell, forming a very 
satisfactory film of dust over the entire surface. ^hen examined 
16 hours later, a considerable proportion of the larvae were dead 
and many of the living revealed the effect of the derris in their 
sluggish movements. The pool was not examined again until 60 
hours after treatment, wj-, en £ i] the larvae were dead, many float- 
ing on the surface of the water. 
