58 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



shaped or knoblike galls on the tips of twigs and branches are 

 characteristic of the work of bark gall aphids belonging to the 

 genera Chermes and Pinevs (1) . The bark-feeding forms are 

 seriously destructive to certain coniferous trees, particularly 

 spruce, fir, hemlock, and pine, and may bring about the death of 

 heavily infested trees. Cone-shaped galls, which form on the twigs 

 of spruce, frequently kill terminals but rarely endanger the life 

 of these trees and are of little importance under forest conditions. 

 On seedlings and saplings in nursery or plantation and on orna- 

 mental trees the formation of these galls is of some consequence, 

 because they kill the tips of branches and tend to stunt and deform 

 the trees. 



Many of these gall-making species have an alternate host upon 

 which they appear in a different form. One alternate form, fre- 

 quently seen on pines, Douglas-fir, fir, and hemlock, appears as a 

 dirty-white wax on the bark of twigs, limbs, and trunk. Another 

 form appears as small tufts of cottony wax on the needles of 

 Douglas-fir. Usually these bark and leaf -feeding forms exude a 

 honeydew upon which a black smut grows, and accumulations of 

 this smut make trees very unsightly. 



Control of these aphids may be obtained by spraying early in 

 the spring, when the young begin to colonize on new growth, with 

 a spray composed of 6 gallons of miscible oil and 1 quart of 40 per- 

 cent nicotine sulfate to 200 gallons of water. In nursery and 

 plantation and on ornamental trees some control of the gall- 

 making form can be obtained by cutting and burning the green 

 galls before the insects emerge in the spring. 



The Cooley spruce gall aphid (Chermes cooleyi Gill.) is the 

 species most frequently responsible for the formation of cone- 

 shaped galls on terminal twigs of blue, (fig. 23) Engelmann, 

 and Sitka spruces in the West. Two or more other species do simi- 

 lar damage. The galls are from 1 to 2 inches long, light green to 

 dark purple, and are formed by the growing together of the basal 

 portion of the needles so as to form chambers between the base 

 of the needles and the stem. These chambers, which are not com- 

 municating, usually contain from 3 to 30 small wingless insects 

 covered with a white waxy coating. The galls turn brown, dry, 

 and hard on the trees after the insects have escaped, and they may 

 persist for many years. 



On Douglas-fir these gall lice appear as small cottony tufts on 

 the underside of the needles. Their feeding punctures cause the 

 needles to turn yellow in spots. Sometimes the damage is so severe 

 as to cause a browning and premature shedding of the foliage. 



The seasonal history is very complicated. The form found on the 

 Douglas-fir needles during the winter represents hibernating fe- 

 males, or stem mothers. These lay eggs early in the spring, and 

 the young, which settle on the tender foliage and feed, later ma- 

 ture into winged and wingless females. The wingless forms deposit 

 eggs, which hatch later into females that will hibernate, while the 

 winged females migrate to the spruce and lay eggs at the base of 

 the needles. The young hatching from these eggs cause the forma- 

 tion of the cone-shaped galls. About the middle of July the forms 



