INSECTS OF THE APHIS TYPE 143 



is used to kill them, such as Paris green or arsenate of lead, and 

 not such a substance as lime, or sulfur or copper sulfate. 



If a man were attempting to poison a skunk or a weasel that 

 was killing his chickens he would -not expect to do it by putting 

 out a bait covered with sulfur, but would use some form of 

 strychnine or arsenic. Precisely the same rule holds with 

 insects. They are merely smaller animals. They take the poison 

 along with the plant tissue into the stomach and are killed. 



Now contrast with this the aphis, which is a conspicuous 

 example of an altogether different type of insects. Most orchard 

 owners are entirely too familiar with the way this insect works. 

 If the owner is on the watch for it he sees first a few little green 

 or black lice on the under side of the leaf, or even on the opening 

 bud, waiting for the leaf to appear. These increase rapidly in 

 number and the leaf begins to curl up because the under sur- 

 face, where the insects are sucking the sap of the leaf, is thereby 

 retarded in its growth, while the upper surface, being less 

 affected, continues to grow normally or nearly so. But the leaf, 

 while it is distorted, does not disappear. It is all there except the 

 juice and no amount of poison applied to it will have any effect 

 on the aphis. It would be exactly as reasonable to expect to kill 

 a mosquito, by putting Paris green on one's hand, as to destroy 

 the aphis with such a poison. The beak of either insect would 

 be pushed through the layer of poison and into the tissues on 

 which it wished to feed and it would draw in the blood of the 

 man or the sap of the plant without any poison whatever. 



Insects of the aphis type have to be attacked in an entirely 

 different manner. And it is a much more expensive method. 

 They must be treated with some substance which will either stop 

 up the pores along the sides of the abdomen through which the 

 insect breathes or else (either by entering those pores or by work- 

 ing on the surface of the insect) will corrode the tissues and 

 destroy the insect. Soapy substances work in the former manner, 

 while the oils and similar substances actually attack the tissues. 



These may seem like very simple statements and so they are. 

 But they are fundamental and are inserted here because so often 

 they are not understood. Indeed, at meetings of fruit growers 



