. ^22 - 
Against "both nosquito larvae and aphids, Dcrris polyantha was norc 
effective than cither of the other two species. In "both cases, in 
aqueous solutions, it showed its superiority (l) in Taringing ahout the 
highest percentage of dca.ths , (2) in the short time it required to kill, 
and (3) in the retention of its virulence. D. polyantha retained its 
virulence in water and v/as toxic to mosquito larvae for a period ranging 
from 13 to 16 days. JD. elliptica and D. philippinensis were toxic for only 
1 to 3 days. 
I>arham (27) in 1926 gave an interesting account of his early work 
with derris, which he regarded as essentially a stomach poison. 
"Starting in the Malay States in 1902, where some field 
trials shoiired it a potent agent for the destruction of mosquito 
larvae, v;ork I'vras continued on my return up to 1907; it was not 
possihle to publish the large amount of ohscrvations in those 
days, and naturally the loss of time made it difficult to use old 
notes. A fairly large scale trial was made in the late Dr. IV. H. 
Maskcll' s garden at Shclford on 13th June, 1904, where the 
G-ooseherries were alive v/ith sav/-fly larvae; the larva.o were 
promptly killed, and the cooked fruit gave rise to no unpleasant 
symptoms in the consumers. 
"In those now far off days a numher of larvae of the 
Small Eggar of good size were put on a spray of leaves 
v/hich had hecn dipped in a suspension of the derris root; they 
were all dead next day, Xirhcn a further supply of larvae was put 
on, the lco,vcs being now dry; the controls had had the leaves 
v/Qtted v/ith v/ater in ca,se mere wetting might have an effect. 
This renev;al of application of larvae continued till the leaves 
became too withered in about ten days; none of the controls 
died, and all of the derris-fed larvae were killed. Open air 
trials showed tha.t the poison still remained active for at 
least a fortnight. Here the effect is clearly a,s a stomach 
poison. 
"On the other hand, a very extensive series of trials 
v/as made upon the black bean aphis and the woolly aphis; in the 
latter case the trials were carried on throughout the summer, 
both v/ith spraying a.nd v;ith careful use of a camel-hair brush 
so as to get thorough v;etting of the patches, which had a millcy 
appearance when treated. The \TOolly aphis is, of course, dif- 
ficult to v/et , but in neither case v;as there anj;- appreciably 
diminution. I cannot but thinlc tha.t the irregular results v;hich. 
have been obta.incd v/ith contact trials ha,ve been due to the 
insects sucking some droplets of the fluid v/hen dislodged ere 
they plunged in their bealcs or in the case of the somewhat 
crude method of ba.thing ca.tcrpillars some of the poison may 
ha.ve been licked up. The slov/ death of mosquito pu.pae (perhaps 
two or throe day's after the larvae) suggests that absorption 
of the extremely insoluble agent talces place, mere contact not 
sufficing. I'fliether or no in some ca.ses there may be a contact 
effect, 'the main utility of the drug must be as a stomach poison. 
