-18- 
et 0.1 gram per liter. 
"liter, whereas rotenone is as effective at 0.005 gm. per liter as it is/ 
Campbell, Sullivan, Smith, and Haller ( 56) in 1934 found 
that rotenone at 1:100,000 killed 46 out of 50 mosauito larvae 
( Culex pipiens , G_. territans , and C« ouinouefascietus ) in 20 
hours, and at 1:200,000 it killed 47. The higher concentration 
killed half the larvae in 151 minutes, as compared with 272 min- 
utes for the lower concentration. 
The larvae o^ Culex pipiens L. and of Aedes vexans (Meig.) 
("A. sylvestris (Theo'b.)) were used "by Ginsburg, Schmitt, and 
&ra.net t ( 112 , 113 ) in 1934 to test the insecticidal value of 
various derris extracts. A fresh supply of larvae was collected 
daily during the testing period and "brought 5nto the laboratory. 
The very young larvae were either entirely removed or were not 
counted in the final results. Only larvae of substantial size, 
apparently fr<3m 3 to 5 days old, were used. This precaution was 
taken "because it had been found previously that the very young 
larvae are more readily killed by toxic chemicals than are older 
ones. Furthermore, the young larvae are more sensitive to sud- 
den changes of either media or atmosphere, as would inevitably 
be brought about by transferring from field to laboratory con- 
ditions. About 50 larvae were transferred to large porcelain 
dishes containing 500 cc. of mixed ditch water and tap ^eter. 
The de?ired amount of extract in various dilutions was then 
added from a pipette and was stirred in with a glass rod. After 
24 hours the dead and living larvae '"ere counted. Several dishes 
were run for each test in order to obtain a minimum of about 200 
larvae. Preliminary tests showed that acetone extracts of derris 
root are very toxic to mosauito larvae. Dilutions equivalent to 
1 gm. of derris root in 10,000 parts »f water or lower invariably 
produced a 100-percent kill of larvae and could not be used for 
comparative tests, therefore only dilutions ranging from 1:10,000 
to 1:80,000 were run in this experiment.. At dilutions of 10,000 
20,000, and 40,000 the kill '-as equally high for all the extracts 
(except No. 7), ranging from 85 to 100 percent. A^ dilutions of 
80,000 the water extracts proved considerably lower in toxicity 
than either the alcohol or the acetone extract. Pure rotenone 
proved much inferior to the extracts in toxicity to mosauito 
larvae. Dilutions of 1 part of rotenone to 1,000,000 and 
2,000,000 parts of water gave 50 and 10 percent kills, respecti- 
vely, while acetone extracts containing similar concentrations 
of rotenone gave 92 and 96 percent kills, respectively. The 
results of toxicity tests of various derris extracts to mos- 
quito larvae were as follows: 
