138 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



years we were in doubt as to where these winged lice went. They could 

 be seen to fly away from the beet fields, but their destination was a 

 mystery. The native cottonwood {Populus balsamifera Linn.) was 

 suspected of being the alternate host, but not until September, 1912, 

 were our suspicions confirmed. The insects were first noticed on the 

 edge of a weedy field where P. hetce had previously been noticed in 

 abundance upon the roots of pigweed, foxtail and blue-joint. As one 

 looked across the field the air above it swarmed with winged lice which 

 were flying toward a row of cottonwoods on the edge of the field. This 

 row consisted of trees in three stages of leaf ripening. Some had lost 

 nearly all their leaves, on others the leaves were still a dark green, while 

 one tree at the end of the row retained its leaVes which were a light 

 yellow in color. To this last tree the majority of the lice directed their 

 flight. Alighting on the leaves they immediately started down the 

 stems to the main branches and down the main branches to the trunk. 

 Every branch was gray with an army of winged aphids all marching in 

 one direction, — down the tree. When the main trunk was reached, 

 the lice crawled down until a suitable crack or crevice was found into 

 which they would crawl. Many continued to the ground and secreted 

 themselves in the leaves, grass, and dirt around the base of the tree. 

 A loose piece of bark pulled from near the base of the tree revealed a 

 mass of the winged lice clustered beneath it. Some were already dead 

 with the abdomen shrunken clear to the thorax. Crawling over the 

 dead bodies were small yellow lice and other winged specimens were ob- 

 served giving birth to these small yellow individuals. The swarming 

 continued until dark and was repeated on a smaller scale on warm, 

 still days throughout the fall. Upon microscopic examination the 

 great majority of winged migrants proved to be Pemphigus hetce, al- 

 though a few specimens of a much larger undetermined species were 

 also observed . . 



Winged individuals have been collected from sugar beets, pigweed, 

 foxtail and blue-joint. 



True Sexes — Sexuales of European Writers 



An examination of the small yellow lice deposited by the fall migrants 

 showed them to be the true sexes. The females are nearly twice the size 

 of the males and each contains a single large egg which shows plainly 

 through the body wall. Each fall migrant gives birth to from four to 

 seven individuals, the majority of which are females. One was observed 

 to give birth to seven young in forty minutes. Both sexes have rudi- 

 mentary mouth parts and take no food, but nevertheless four molts 

 are passed through. The time of molting varies in different individuals 

 but in nearly every case is completed at the end of four days after birth. 



