Sept. 3,1917 Quassia Extract as a Contact Insecticide 519 



so that the aphids were against the wire screen but not in contact with 

 the powder. Fifty minutes later most of the aphids were "stupid"; 

 5 hours later 2 of them were dead; and the following morning 15 were 

 dead, and the others had crawled away. 



At II a. m. leaves from nasturtiums, apple, ragweed, and snowball, 

 all bearing many aphids {Aphis rumicis, Aphis pomi De Geer, Macrosi- 

 phum ambrosiae, and Aphis vihurniphila Patch), were dusted with the 

 quassiin powder. Forty-five minutes later most of the aphids were inac- 

 tive, and by 4.30 p. m. practically all of them were dead. 



At 12 noon leaves from mulberry and pear trees, bearing many fall 

 webworms (caterpillars of Hyphantria cunea Dru.) were dusted with the 

 quassiin powder. By 2.30 p. m. nearly all of the webworms were inactive, 

 and by 4.30 p. m. all of them were apparently dead; the following 

 morning at 10 o'clock all were still apparently lifeless, except a few 

 which were slowly reviving from their "stupor"; two days later still 

 most of them had revived and were as active as usual. 



At 4 p. m, several mulberry leaves were cut into small pieces and then 

 some of the quassiin powder was mixed with them; next, 20 medium- 

 sized silkworms (larvae of Bombyx mori L.) were placed upon the mix- 

 ture of leaves and powder. Half an hour later three silkworms were 

 apparently lifeless, and the others appeared weak and sick; they did 

 not seem to eat the bits of leaves, but crawled away from them, and 

 consequently it was necessary to confine them in a box with the poisoned 

 food. The following morning all of them were apparently dead, and 

 they never revived thereafter. 



A microscopical examination shows that the minutest particles of the 

 quassiin powder are sufiiciently small to pass through the spiracles of 

 aphids and into the tracheal trunks for some distance; but, before they 

 can come into contact with the nervous system (supposing that this 

 system is the tissue vitally affected) , they must pass through the smaller 

 tracheal branches and even then through the tracheal walls in order to 

 come into contact with the nerve cells. Furthermore, it is scarcely 

 possible that they pass even through the spiracles of aphids and fall 

 webworms because the spiracles are well guarded by hairs (22, p. 104). 

 In view of the preceding, it seems that the exhalations alone from this 

 powder killed the aphids and silkworms employed and rendered the fall 

 webworms inactive for about a day. 



(6) Effects of Quassia Powder 



The preceding experiments were repeated by dusting quassia powder 

 upon aphids from nasturtiums and snowballs, and upon silkworms and 

 fall webworms. During the first 24 hours no effects were observed, 

 except that a few of the smallest aphids died and that the silkworms 

 were rendered slightly "stupid" for a few hours, but the webworms 

 apparently were not affected at all. Some of the aphids were even 



