BEET AND ^SPINACH INSECTS 103 



lamb's quarters but has also been reported as infesting the 

 roots of the following plants : yarrow, knotweed, dock, aster, 

 goldenrod, horse-weed, winged pigweed, foxtail, salt-grass, 

 blue-joint grass, wheat, flax and alfalfa. 



The insect passes the winter in two forms, either as wingless 

 viviparous females on the roots of its food plants or as eggs on 

 the bark of two species of cottonwood {Populus angustifolia 

 and P. halsamifera) . The plant-lice that have survived the 

 winter on the roots begin to give birth to living young in April 

 or May, producing another generation of wingless viviparous 

 females. Reproduction continues in this way until mid- 

 summer, when winged forms begin to appear. Only about half 

 of the lice acquire wings, the others continue breeding on the 

 roots throughout the season. The form found on the roots is 

 about i inch in length, pale yellow in color and has the pos- 

 terior part of the abdomen clothed with a white flocculent mass 

 of waxy filaments. The remainder of the body is dusted with 

 a white powder. Infested roots appear to be covered with a 

 white or grayish mold. The winged forms produced on the 

 roots are slightly larger than the wingless forms. The abdo- 

 men is greenish, the thorax, head and antennse bluish black, 

 lightly dusted with the whitish powder and there is only a 

 little of the white flocculent material on the tip of the body. 

 These winged forms begin to appear in midsummer and con- 

 tinue until the end of the season but are most abundant in 

 September and October. They migrate to the cottonwood, 

 where, on the bark of the trunk, each female gives birth to four 

 to seven young, part males and part females, the latter pre- 

 dominating. These forms lack functional mouth-parts and do 

 not take food. They molt four times in as many days and 

 after mating the female de])osits a single pale yellow eg^ in a 

 crevice of the bark, which usually rests on a mass of bluish 

 white waxy threads. The eggs hatdi about the first of the 

 following May and the young plant-louse crawls out on the 



