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Cooley spruce gall adelgid, Adelges cooleyi

Fig. 48  
Non-tufted and tufted cooley spruce gall adelgids on Douglas-fir foliage. Note wool-like appearance of tufts.
Fig. 49 
On Douglas-fir, infestation by cooley spruce gall adelgid is characterized by white tufts from spring to fall.
Fig. 50  
New gall (above) on spruce caused by cooley spruce gall adelgid. Old gall (below) is necrotic and brown.
Fig. 51 
Cross-sectional difference between cooley spruce gall adelgid (left) and Pineus.

Distribution:  Throughout B.C. wherever Douglas-fir is established.

Tree Species Attacked: Attacks alternate between Douglas-fir and Sitka, Engelmann, or white spruce. All ages of trees are susceptible, but the damage is most severe on immature spruce.

Insect Description & Damage Symptoms: On Douglas-fir, adults are about 0.1 cm long, oval, and light to dark brown in colour. At maturity they are completely covered with white, waxy wool and appear, from spring to fall, as stationary wool tufts on the underside of needles. The needles of light to moderately infested trees exhibit chlorotic mottling where individual adults have fed. Attacked needles may also be twisted. Severely infested foliage may be completely chlorotic and drop prematurely. On spruce, the adult is similar to that found on Douglas-fir. Infested spruce display cone-like galls at the ends of branches. These galls are 1 to 8 cm long with separate chambers. New galls are green, pink, or purple, and flexible; the chambers are closed and may contain aphids. As they age, galls become brown, hard, and brittle. The chambers are open and empty. Old galls may persist on spruce branches for several years.

Damage: On Douglas-fir, light infestations are very common, though not seriously damaging. Significant damage, however, including needle loss and growth reduction, occurs sporadically when young trees are severely attacked. Heavy infestations and damage may be indicative of environmental stress. On spruce, repeated attacks can produce stunted, deformed trees, but normally, cooley spruce gall adelgid is not a serious concern in spruce stands.

Similar Damage: Some species of the woolly aphid genus Pineus form galls on spruce that can be confused with Adelges galls. The Pineus gall chambers are inter-connecting, while cooley spruce gall adelgid chambers are non-connecting.

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BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 12, 2002