36 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 47 



a jumping plant louse. Formation of each gall is stimulated by 

 a tiny insect that feeds and lives inside the gall. The small, yel- 

 lowish-brown adults pass the winter in bark crevices of trees or 

 in the debris under trees. About the time leaf buds unfold, the 

 female deposits eggs on the under sides of leaves. When the 

 eggs hatch, each young insect crawls to the upper side of a leaf, 

 settles down, and begins to feed through a short beak. The leaf 

 tissue grows around the insect in characteristic fashion to form 

 a gall. By September the insect completes its development and 

 emerges as an adult through a slit it makes in the base of the 

 gall. At that time of year, insects of this species may make 

 nuisances of themselves by flying into houses. 



Control Measure 8 (end of circular) applied to trees about 

 the time the leaves begin to unfold. 



Witches'- Broom, fig. 27. — Abnormal growth that results in 

 bunches or tufts of small twigs on the limbs and branches of 

 hackberry is commonly called witches'-broom. Apparently the 

 brooms do little harm to an affected tree, but they detract from 

 its appearance. A tiny mite, Aceria snetsingeri Keifer, and a 

 fungus, Sphaerotheca phyloptophila Kell. & Swingle, are asso- 

 ciated with witches'-broom, but it is not known whether either 

 or both stimulate the peculiar growth. 



Control. No control for witches'-broom on hackberry has 

 been developed. 



HICKORY 



Yellow-Necked Caterpillar, fig. 10. — See under Crabs and 

 Hawthorns. Control Measure 1 or 2 (end of circular). 



Hickory Bark Beetle, Scolytus quadrispinosus Say. — Small 

 emergence holes in the bark of the trunk and branches of a hick- 

 ory tree are signs of an infestation by this species. The adults 

 are dark brown beetles, each less than one-fourth inch long. 

 After emerging from beneath the bark, each beetle feeds for a 

 short time on young twigs, then bores through the bark of the 

 same or a different tree, and constructs a gallery between the 

 bark and the wood. Along the edges of the gallery, the female 

 deposits eggs that give rise to white, legless grubs, which cause 

 further and more extensive damage. 



Control Measure. This species is especially injurious to 

 hickories growing in parks. Heavily infested trees should be 



