5i8 Journal of Agricultural Research voi. x, No. 13 



Twenty-four hours after applying the nicotine-sulphate solution the 

 following aphids were dead : None of those sprayed with tap water after 

 5 and 10 minute intervals; a few of those on the kale and nasturtium 

 leaves sprayed with tap water after a 20-minute interval; several of 

 those on the kale leaf and nearly all on the nasturtium leaf sprayed with 

 tap water after a 30-minute interval; nearly all belonging to the four 

 species sprayed with tap water after a 60-minute interval; and all 

 belonging to the four species sprayed with tap water after a 1 20-minute 

 interval. 



The foregoing results show that nicotine sulphate acts very quickly, 

 while quassia extract acts very slowly. These results also indicate that 

 a shower 2 hours after the application of these insecticides does not 

 affect the efficiency of the nicotine sulphate, while it greatly reduces the 

 efficiency of quassia extract. 



PHARMACOLOGICAL EFFECTS OF QUASSIIN 



The preceding experiments show that quassia extract kills aphids only 

 by coming in contact with them, but it still remains to be shown how it 

 kills them. This phase of the work involves a careful study of the 

 physiological effects of quassiin on aphids and of what tissue is vitally 

 affected. 



I. — PHYSIOLOGICAL EFFECTS OF QUASSIIN 



To determine how quassiin in the form of powder and in spray solu- 

 tions affects insects when dusted or sprayed upon them, the physiological 

 effects of this substance on the insects were observed. Of the various 

 insects used in the experiments it was ascertained that quassiin is fatal 

 only to aphids; consequently the following discussion of results will be 

 devoted chiefly to this family of insects, and the effects of this substance 

 on the other insects utilized will be noted only here and there. 



(a) Effects of Quasshn Powder 



At the outset a purified powder of quassia, already mentioned on page 

 509, was used. This powder is light yellow and is supposed to be largely 

 quassiin. It is intensely bitter, has a faint odor, and is disagreeable to 

 work with, for after a few moments, regardless of how carefully it is 

 handled, a bitter taste is experienced which sometimes lasts half a day, 

 and consequently a headache often results. It would thus seem that 

 the odor, and probably the minutest particles of the powder suspended 

 in the air pass into the nose and mouth and give rise to the sensation of 

 having tasted it. 



To determine whether the exhalation from the quassiin powder alone 

 is sufficient to kill aphids, a watch glass was completely filled with the 

 powder; then a wire screen was laid over the powder and a nasturtium 

 leaf, bearing about 45 aphids {Aphis rumicis), was laid upon the screen 



