PLANT LICE. 185 
show a tendency to turn yellow or to wither, and ascertain what 
kind of injury it may be suffering from. It would often hap- 
pen that the determination of the kind of insect affecting the 
roots would determine the best method of cultivation for the 
next season.” (Osborn). 
Aphis brassice Linn. (The Cabbage Plant-louse ). 
This plant-louse (Fig. 155) occurs in such immense num- 
bers on the cabbage and related plants that it is the most de- 
structive species of plant-louse infesting the vegetable garden. 
It is sometimes equally numerous on the wild mustard, and it 
would not be considered a bad habit if it concentrated all its 
energies to subduing that weed. There are few seasons in which 
Fic. 1541%4.—Aphis maidi-radicis Forbes: a, winged viviparons female; b, apterous 
viviparous female; c, apterous oviparous female. After Forbes. 
it does not appear in immense numbers, and in this case the 
plants become so weak that they fail to grow. Turnips and 
radishes also suffer severely, but to a less extent. The damage 
is especially severe on young plants just set out. The insect re- 
mains on the plants till frost. 
“The wingless viviparous female is rather a long oval in 
form, of a greenish-gray color, with a series of black spots on 
each side of the back, becoming larger in size toward the tip. 
This coloration is usually obscured by the whitish, mealy or waxy 
secretion which covers the body of these insects. The antenne 
are green, with black tips, and the eyes and legs are black. See 
Hig. 137,10. 
