INSECT ENEMIES OF EASTERN FORESTS 595 
borealis) , black oak (Q. velutina), and water oak (@. nigra) through- 
out the eastern part of the United States and westward into Texas. It 
forms a rough woody swelling on the shaft of twigs and iarger branches 
ranging from 14 inch to Ve inches in diameter. Fr equently several 
galls fuse together to form a prac- 
tically continuous mass of abnor- 
mal tissue. The gall wasps issue 
early in the spring and deposit 
eggs in the starting buds.. The 
young insects develop in small blis- 
terlike leaf galls, usually on or 
near the veins. Insects of the al- 
ternate generation probably issue 
in midsummer and cause the bet- 
ter - known knotty - branch galls. 
The species is usually localized on 
certain trees of a group. At times 
it becomes numerous enough to 
cause the death of twigs or good- 
sized branches. ‘Trees so affected 
may lose their symmetry, and oc- 
casionally whole trees have been 
killed. The principal economic - : 
damage is done to specimen shade — Figure 176.—The gouty oak gall (Cal- 
trees. Since the insects responsi- lirhytis punctata). (After Felt.) 
ble for these growths are protected 
within the woody tissue of the galls during their developmental period 
and for most of their lives, the only practical control consists of cutting 
and burning the freshly swollen twigs as soon as the galls are obser ved 
and before the insects within complete their development and emerge 
as adults. 
The galls formed by Callirhytis (Andricus) cornigera (O. S.), 
Figure 177.—The horned oak gall (Cullirhytis cornigera). 
