Common name: Eastern spruce gall adelgid and Cooley spruce gall adelgid
Scientific name: Adelges abietis and Adelges cooleyi
Hosts: The eastern spruce gall adelgid attacks Norway and white spruces most frequently, but red, black and Engelmann spruces may be hosts as well. Colorado blue spruce is occasionally damaged. Cooley spruce gall adelgid most frequently infests Colorado blue spruce, but can infest Sitka, and Engelmann spruces. Douglas-fir serves as a secondary or alternate host during part of the insect’s life cycle. These two species of small, soft-bodied insects infest spruce species during the course of rather complicated life cycles. Adelgids are aphid-like insects. Their feeding leads to the production of galls that can disfigure the host.
The galls formed by the feeding at the nymph stage of both insects inflict the most damage. These cone-like growths will stunt the growth of the twigs on which they formed and distort the symmetrical beauty of the tree. Severe infestations can cause a branch to be killed. Because the galls of the eastern spruce gall adelgid develop at the base of shoots, the stems are weakened, making them more likely to break under the weight of snow or other physical stress. This basal location makes it impossible to remove galls without removing the entire twig, again detracting from the tree’s form and beauty. The eastern spruce gall is pineapple-shaped, greenish-purple, and about ½ to 1 inch long at the base of seasonal twig growth.
The Cooley spruce gall adelgid produces a 1 to 3 inches long gall on the tips of new growth of host spruces. This makes them more easily removed. If they have settled on Douglas-fir to feed and overwinter, the feeding will cause prominent yellow spots on needles that can become bent and distorted. If an infestation is heavy, the tree can become so covered with the characteristic white egg masses that it can look snow-covered.
Eastern spruce gall adelgid overwinters as immature females on branches near the terminal (end) buds. The adult female is a small, bluish-green, sucking insect covered by cottony, waxy strands. Eggs will be laid at the base of the buds before they open in early spring. When they hatch 7 to 10 days later, the young nymphs crawl to the base of the tender, new needles. Nymphs range in color from yellow to blue-green and can grow to about 1/8 inch long. As they feed, they form their characteristic gall which will completely enclose and protect them from weather, disease, and predators as they mature. While the gall is forming, the spruce shoot is growing through it, leaving the gall behind at the base of the stem. In August, the galls dry out and crack open, exposing nymphs that will crawl onto the needles and molt to become winged adults. These adults will fly to spruce branches where about 100 eggs are laid under webs of white, cottony wax on the unprotected new growth. Within a week, the eggs will hatch and the new nymphs feed for a short time on new growth before settling near the buds to overwinter. Two generations are produced each year.
The Cooley spruce gall adelgid has a complicated life cycle, which takes two years to complete. The insect overwinters as adults. Adults are dark reddish-brown with two pairs of wings and threadlike mouthparts used for sucking the plant juices from host trees. Eggs are laid in spring under white, cottony wax masses near the terminal bud. Nymphs will hatch to feed at the base of needles of the expanding buds and form the multi-chambered galls that enclose and protect them. Nymphs are small, yellowish ovals, fringed with white waxy threads.The galls will dry up by midsummer and burst open, exposing the nymphs.
The newly emerged winged adults will either continue their life cycle on the primary host spruce or fly to the alternate host, Douglas-fir, to lay the next generation of eggs. The population that lives and overwinters on the Douglas-fir will not form galls. Feeding damage, in the form of yellow spots and distorted needles may occur on this host. When this generation emerges the following spring, winged forms are produced and they will fly back to the primary host, spruce. At this time, they will lay the eggs that emerge to produce the gall-forming nymphs. If the adult stays on the host spruce, it will overwinter on twigs. The insect can complete its life cycle on spruce alone, or on both spruce and Douglas-fir. Injury will be more serious when the insect alternates between the two.
Cultural management:
Removing galls which are still green is possible and usually can be done before mid- July. If the infestation is light, the galls can be hand-picked, thereby avoiding pruning, which will further disfigure the tree.
Chemical management:
Insecticides are available to control adelgids. Look for signs of infestations in late March to early April. Since adelgids become active before the trees begin to show signs of breaking dormancy, it is important to start looking for them early. If you wait too long to spray chemical controls, the white cottony egg masses will be laid and will be impermeable to spray applications.
If Cooley spruce gall adelgid needs to be controlled, make sure to include any nearby Douglas-fir trees in your coverage. Douglas-firs should be treated during their dormancy or when crawlers are first visible.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).