•&cr- 
of De ris phi.lippinensis in "bringing about the highest percentage 
of deaths in the shortest time -was 3:1,000. Solutions either 
more dilute or more concentrated then 3:1,000 were less effective. 
Concentrations of 1:1,000 killed 19 percent of the larvae in 5 
days; lower concentrations showed no effect at all. A concent- 
ration of 3:1,000 or higher retained its toxicity against mos- 
quito larvae 13 to 16 days, Against both mosquito larvae and 
aphids, Derris polyantha was more effective than either of the 
other two species. In aqueous solutions it showed its superiority 
against 'both insects (l) in bringing about the highest percentage 
of deaths, (2) in the short time it reouired to kill, and (3) in 
the retention of its viralence. Derris polyantha retained its 
virulence in water and 'as toxic to mosquito larvae for 13 to 16 
days. Derris elliptica and D. philippinensis "'ere toxic for only 
1 to 2 days. 
Durham (78) in 1926 gsve an interesting account of his early 
i,"ork with derris, '"hich he regarded as essentially a stomach 
poison. Field trials started in the Malay States in 1902 showed 
it to be a potent agent for the destruction of mosquito larvae. 
Kelsall et al. ( 159 ) in 1926 reported that derris, at approxi- 
mately 1 -pound oer 100 imperial gallons, added to a large tank of 
water verv heavily. infested with mosauito larvae, killed all the 
larvae in 3 or 4 days. 
The Canada Experimental Farms, Division of Chemistry ( 57 ) in 
1927 stated that derris had been found very effective as an agent 
in mosquito-control work. 
In 1929 the I^oerial Institute ( 146 ) reported the results of 
tests made by the Entomological Branch of the Department of Agri- 
culture in Nigeria, Africa, with TephrosiF vogelii . An aqueous 
extract of the leaves ^as tested on mosquito larvae, but the larvre 
thrived even in strong solutions. Adult mosquitoes seemed tb be 
attracted to the extract for oviposition. 
Davidson (67) in 1930 reported that when pure rotenone dis- 
solved in acetone was added to a tub of ,- 'ater to give a rotenone 
concentration of 1:1,150,000, from 98 to 99 percent of the culicine 
larvae "ere killed within 5 days, the eggs present hatched, and the 
resultant larvae died "dthin 2 days. Rotenone at 1:2,300,000 killed 
95 percent of the larvae in 6 days, but the remainder transformed 
into pupae, the eggs present hatched, and 20 percent of the resultant 
larvae survived. Larvae and eggs in untreated tubs showed no ab- 
normal mortality. 
Fulmer ( 90 ) in 1930 wrote that derris destroyed mosquito larvae 
when apT)lie«5t at the rate of 1 pound to each 1,000 imperial gallons 
of the m ater in which the larvae a: e present. 
