Sept. 3. I9I7 Quassia Extract as a Contact Insecticide 523 



insecticidal properties of this substance and to the fact that water does 

 not spread it well, the efficiency of it when dissolved in soap solution 

 would seem to be due to the fact that the soap solution spreads it in such 

 a manner that a larger amount of it may reach the nervous system. It 

 now remains to be shown how it reaches the nervous system, for there 

 is no other plausible way of explaining its effects on aphids. 



Experiments in which a soap-solution extract of quassia chips was 

 used, in the same manner as described on pages 514 and 515, demon- 

 strate that the exhalations from this spray mixture do not kill aphids, and 

 that the mixture does not act as a stomach poison when applied as a 

 spray. On page 515 it is further shown that soap solution containing 

 no quassia extract but the same amount of soap as employed in the 

 soap-solution extract has no apparent effect on some aphids, and but 

 very little on other aphids. 



While the spray mixture was being applied, some of the fine spray 

 might have been taken into the respiratory system and possibly came 

 into contact wdth the nerve cells, but, comparing the effects of this spray 

 mixture with that containing no soap, the writers are inclined to believe 

 that a larger amount of the quassia extract is required in order to produce 

 the results observed. Owing to the fact that soap solutions have weak 

 surface tensions, they adhere well to the surfaces of plants and insects; 

 they spread readily, and consequently should pass freely into the spiracles 

 of insects. Under the following heading it is shown that they not only 

 pass into most of the larger tracheae but also come into direct contact 

 with the nerve cells. 



The senior writer (22, p. 92) attributed the abnormal behavior ex- 

 hibited by aphids which had been sprayed with a solution of nicotine to 

 motor paralysis, but at no time while using quassiin on aphids was a 

 similar behavior observed. While nicotine acts quickly and causes pro- 

 nounced symptoms, quassiin acts very slowly, and the behavior of aphids 

 poisoned by it is so normal that the few abnormal reactions exhibited 

 are generally overlooked. Soon after being sprayed with a nicotine 

 solution, aphids remove their beaks from the plants and wander about 

 considerably, and sooner or later they fall paresized from the plants, 

 after which they soon die. Aphids sprayed with a solution of quassia 

 extract are no more irritated than when they are sprayed with water. 

 While being sprayed, they lie flat on the leaves, and later seldom remove 

 their beaks from the plants; consequently they wander about little. 

 Usually they do not begin falling from the plants till three or four hours 

 after being sprayed, and by that time most of those that fall are dead. 

 As a rule they die quietly with the beaks stuck into the plants, and in 

 most cases it is necessary to touch them before being able to decide 

 whether they are dead or alive. While practically all of the aphids 

 sprayed with a nicotine solution fall from the plants before they die, not 



