88 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 47 



Willow — continued Y 



aphid 68,69 



borer, poplar and 59 Yellow-necked caterpillar 16, 17, 36 



Witches'-broom 35,36 Yew (taxus) . . . 69,70,71,72 



Wool sower gall 52, 53 



Woolly Z 



elm aphid 29 



hawthorn aphid . . . . 16, 17 Zimmerman pine moth .... 58 



