Terminal galls of Cooley spruce gall adelgid. Courtesy of Cathy Thomas, PDA
Adelges cooleyi (Gillette)
- Colorado blue spruce
- Occasionally found on other spruces
- Alternate host: Douglas-fir (see Needle Discoloration and Injury section for Cooley spruce gall adelgid on Douglas-fir)
Symptoms and Signs
Throughout the Year
- Green, purple, or brown, pineapple- or pinecone-shaped galls, 1½–2½ inches (4–6 cm) long, on the tip of new growth
Causes of Similar Symptoms
- None; galls may be mistaken for cones
The Cooley spruce gall adelgid is a small, soft-bodied, black insect that may be winged or wingless. It possesses piercing-sucking mouthparts to suck sap from its host. On spruce trees, its presence can be identified by the pineapple- or pinecone-shaped swelling or gall. This gall is only found at the tip of new growth. Galls are green or purple in color and turn brown as they dry out in the summer. When dried, they may be confused with cones.
Biology and Life Cycle
The Cooley spruce gall adelgid overwinters as immature females. On spruce, these overwintering forms can be found in the bark crevices of twigs (Figure 1), just below the buds or around the base of the buds. In March and April, the overwintering immatures feed on sap and gradually swell. They secrete long, waxy filaments over their bodies as they mature (Figure 2). Shortly before bud break, each female produces a cluster of 150–200 eggs inside this mass (Figure 3). The brownish nymphs emerge from the eggs as the spruce buds are opening. They immediately crawl into the bud and begin feeding on the elongating needles.
Figure 1. Overwintering nymph in bark crevice. Courtesy of Sandy Gardosik, PDA
Figure 2. Nymphs covered with waxy filaments. Courtesy of PDA
Figure 3. Cluster of eggs laid under protective waxy threads. Courtesy of Whitney Cranshaw, Colorado State University,
By the time eggs hatch, the bases of the newly expanding needles have already started to swell due to feeding by the overwintering form. When the newly emerged nymphs feed, they inject a toxin through their saliva that causes further swelling of the needle bases. Eventually, the needle bases fuse together, forming a terminal gall (Figure 4). Each nymph is contained in an individual chamber, where they will continue to feed on the succulent tissue inside the gall (Figure 5).
Figure 4. Fused needle bases forming a terminal gall. Courtesy of Cathy Thomas, PDA
Figure 5. Adelgids growing in chambers inside a gall. Courtesy of Sandy Gardosik, PDA
The gall turns brown and opens in midsummer, and the mature nymphs emerge (Figure 6). They move to the needles, molt into winged adults, and will either remain on the spruce or fly to a Douglas-fir tree (Figure 7). (See Cooley Adelgid on Douglas-fir for life history of that host.) In fall, winged adults from Douglas-fir may travel back to the spruce tree to produce another, non-damaging generation. This fall generation, which includes both male and female adelgids, will produce the overwintering forms by mid-October. While the Cooley spruce gall adelgid alternates its life cycle on two different hosts, it does not require both hosts to complete its life cycle. It may cycle continuously on spruce or Douglas-fir.
Figure 6. Browned galls after release of adelgids. Courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org (#5369749)
Figure 7. Winged adult adelgid. Courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org (#1326081)
Calendar of Activities
Monitoring and Management Strategies
- When planting, separate Colorado blue spruce and Douglas-fir trees; this will not eliminate problems, but it may help lessen the severity.
- Scout for brown galls in late fall, winter, and early spring to note which trees had a problem.
- Scout for overwintering nymphs using a 15X hand lens.
- Growing degree days: Recommended control against nymphs should occur in the spring as nymphs begin to swell, before waxing over, at 22–81 GDDs and then in the fall at 2,800–3,000 GDDs.
- Threshold level: Treatment is warranted when 5 percent of trees have 10 or more galls.
- At the end of the season, evaluate results and update records.
- Encourage natural predators such as lacewings,predatory bugs, and fungi. Refer to Appendix B: Biological Controls Photo Chart for pictures.
- Pruning: Remove and destroy unopened green galls on trees before the release of mature nymphs (usually mid-July).
- Dormant oil: To control overwintering nymphs, apply in early spring or late fall (late October/early November) when trees are not actively growing.
— Only apply oil when temperatures are above freezing.
— Oil will remove “bloom,” or blue color, from blue specimens.
- Spring insecticide: Apply in mid-April when greenish-black adelgids are still exposed, before waxy filaments cover the immature females, and eggs are present; temperature should be above freezing.
- Fall insecticide: Apply in late September through October; thoroughly cover branches and buds. This is the most reliable time to spray.
- A general rule for fall application is to wait until after the first frost to guarantee that nymphs will be settled when the spray is applied.
- Only plant pest-free trees from a reputable source.