220 MANUAL OF VEGETABLE-GARDEN INSECTS 



Fig. 137. — Wingless vi- 

 viparous female corn- 

 root aphis (X 13). 



During the summer only two forms of the aphids occur, wing- 

 less and winged vi\ii)arous females ; males and egg-laying 

 females are not produced till October or 

 November and constitute the last genera- 

 tion of the season. From eleven to 

 twenty-two generations are produced 

 annually, each female giving birth to 

 nearly fifty young.. With the advent of 

 cool weather, wingless egg-laying females 

 and wingless, or rarely winged, males 

 are produced. The small black eggs are 

 deposited underground in the galleries of 

 the ants where they are cared for till 

 the following spring. The full-grown 

 viviparous female (Fig. 137) is about yV 

 inch in length, bluish green, dusted with a whitish waxy 

 pulverulence. The head and transverse bands on the thorax 

 are black. In the winged form, the head and thorax are 

 black or dark brown and the abdomen 

 three distinct black 

 spots on each side 

 (Fig. 138). 



By the time the 

 corn is planted and 

 comes up, the 

 aphids have become 

 crowded on the 

 roots of the weeds 

 and many winged 

 forms have devel- 

 oped. At this time 

 the weed roots have 

 become hardened and are thus less favorable for the develop- 

 ment of the lice. The ants transfer many of the wingless 



IS 



pale green with 



Fig. 138. 



Winged viviparous female corn-root 

 aphis (X 16). 



