Plant-Lice 



for many years known in the hop plantations in central New 

 York and in southern Wisconsin and has within the last ten 

 years made its appearance in the extensive hop-growing regions 

 in Washington, Oregon and northern California. All through 

 the Middle and Southern States occasionally hop plants are grown 



in door-yards and this plant-louse is 

 found practically every season upon these 

 plants. The hop is an annual plant, dy- 

 ing down to the ground with the first 

 frost in the autumn. It is obvious, 

 therefore, that the plant-louse is to be 

 found upon some other plant during the 

 late fall, winter, and early spring. This 

 alternate food plant as it is called is 

 the plum. Just why plum trees are nearly 

 always found in the immediate vicinity 

 of hop yards is a mystery. The winter 

 egg of the louse is found upon the plum 

 tree usually at the base of the buds and 

 sometimes under the scales of a bud. 

 From these eggs in the spring hatches 

 the first generation which is composed entirely of virgin females 

 and the individuals of this generation are known as the stem- 

 mothers. In two or three days after hatching, having migrated 

 to the minute leaves bursting from the 

 buds, they begin to give birth to living 

 young, these also all being females. 

 Every day of her existence the stem- 

 mother gives birth to several young 

 varying in number from two to seven or 

 eight. Each of these after reaching the 

 age of about eight days begins in its 

 turn to give birth to living young, so 

 that the stem-mother may live to see 

 her grandchildren of the fourth or fifth 

 generation. The third generation ac- 

 quires wings, although all are still 

 females. By the time the winged 

 generation makes its appearance the 

 hops will have begun to come up in 



266 



Fig. 162. — Phorodon hu- 

 muli: eggs. (From Insect 

 Life.) 



Fig. 163. — Phorodon humuli: 

 stem-mother. { From Insect 



Life.) 



the fields and the lice 



