FOES AND FRIENDS OF THE PLANT 211 



sure to see ants running up and down the stem. The 

 ants are very fond of a sweet juice which the plant lice 

 produce, and may sometimes be seen stroking them to 

 make them produce more of it. This is sometimes 

 spoken of as "milking," and the plant lice are often 

 called "ant cows." 



The eggs hatch out into plant lice like the parent, 

 only smaller. These small plant lice grow rapidty and 

 soon produce others like themselves. There may be 

 several broods in a season. 



In fact, if we started with but a single rose aphis at 

 the beginning oiaT season and all that are produced 

 should live, their weight at the end of the season would 

 be equal to that of all the people in the world taken 

 together. 



A curious fact is that after a number of broods with- 

 out wings, a brood with wings makes its appearance. 

 This allows the insect to spread to other places. 



Hop aphis. These seem to pass the winter in the hop yards, 

 and appear in the spring as wingless forms on the pollen-bear- 

 ing vines. Afterward winged forms appear. They some- 

 times do a great deal of damage to the vines. They may be 

 comgletely^contrpjled by sprays of kerosene^emulsipn and 

 tobacco decoction or of whale-oil soap and quassia extract. 

 (California Experiment Station, Bulletin 160, 1904.) 



Grain aphis. In moist warm spring seasons the grain 

 crops are sometimes greatly injured by the green grain 

 alibis. No practical way has thus far been found of reaching 

 and destroying it. 



