Cooley spruce gall adelgid
Order: Hemiptera
Family: Adelgidae
Description
Cooley spruce gall adelgids (Adelges cooleyi) are gall forming hemipterans. This species is widely distributed throughout the Rocky Mountains and the Cascade Range of western North America. During the spring and summer, adults appear as white, cottony spots on affected trees. When infestations are heavy, entire trees can be covered in a white cottony substance, which is produced by females to protect the eggs. In early stages, individuals are around 1.3 mm (1/20 inch) in length and have black, flat, oval bodies with a protective coating of white cotton-like wax. The egg masses are white, cotton-like, and deposited on spruce twigs.
Quick Facts
- Cooley spruce gall adelgids are small insects often covered with a white, cotton-like wax.
- Their feeding introduces a compound to plant tissues that promotes the formation of galls. Galls begin to form on spruce trees in the spring or beginning of summer. Young galls are green but gradually turn brown by mid-summer. The galls can be mistaken for pinecones.
- Cooley spruce gall adelgids typically complete their life on both spruce and Douglas-fir but tend to form galls only on spruce trees.
- Feeding injuries on Douglas-fir appear as yellow spots and bent needles, while the injury on spruce is usually only aesthetic. If occurring in large numbers, the adelgids can affect seed production in Douglas-fir.
Adults of the Cooley spruce gall adelgid. Note the white, cotton-like substance covering the insects. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Blue spruce with galls produced by the Cooley spruce gall adelgid. Plant fluids can be seen protruding from the gall, indicating that adults will soon emerge. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Broken gall showing the developing Cooley spruce gall adelgids on a blue spruce. Image credits: Whitney Cranshaw, Colorado State University, Bugwood.org
Beginning stages of a gall on a Sitka spruce. Image credits: Christine Buhl, Oregon Department of Forestry, Bugwood.org
Gall formed by the Cooley spruce gall adelgid. Notice the browning of the gall, indicating that the winged form has emerged. Image credits: William M. Ciesla, Forest Health Management International, Bugwood.org
Life history and habits
Cooley spruce gall adelgids alternate between two hosts, Douglas-fir and spruce, and take one year to complete their life cycle. Female nymphs overwinter underneath young spruce branches. When spring begins, the overwintered female nymphs mature into adults before laying eggs near developing buds. The eggs hatch during bud break and the first instar nymphs migrate to new growth where they feed at the base of developing needles, resulting in the formation of galls. Immatures actively feed and develop in chambers inside the gall. The galls are green and inconspicuous at this stage. In mid-summer, winged adults emerge from galls which causes the chambers to open and the gall to dry out. After emerging, most of the adults migrate to Douglas-fir to lay eggs and the abandoned galls become increasingly noticeable after a few weeks.
No galls are produced on Douglas-fir. In late summer, some of the females develop wings and migrate to spruce to deposit eggs. Overwintering nymphs emerge in the fall. Females that do not migrate to spruce produce overwintering nymphs on Douglas-fir.
Injury
The saliva of Cooley spruce gall adelgids induces physiological changes in the host tree that result in the formation of galls. Often, the presence of galls on a tree is an indicator of infestation. On spruce, galls are formed on the tips of branches and typically kill new growth. However, injury to spruce trees is aesthetic and causes the tree little to no harm. The cucumber-shaped galls are around 5-10 cm (2-4 inches) in length. They are found on the new growth of spruce trees and are often mistaken for pinecones. In the spring, the galls are light green but will dry out and turn brown in the summer. Most galls are formed on the shaded sides of trees, and individual trees seem to vary in their susceptibility to the adelgids and likelihood of developing galls.
On Douglas-fir, immatures of the Cooley spruce gall adelgid feed on the needles which can cause discoloration, distortion, and premature needle drop. In large numbers, these insects can affect seed production. They also excrete honeydew which can lead to the growth of sooty mold on the tree.
Monitoring
In areas such as British Columbia where the Cooley spruce gall adelgid is a significant pest of seed orchards, monitoring involves inspecting a single one-year old terminal for overwintering Cooley spruce gall adelgids on 100-150 trees. The shoots should be located on central or terminal branches below 2.5 m (8.2 feet) in height. It is recommended that sampling be conducted before overwintered individuals begin secreting their woolly coverings, which can obscure counts. While no economic or action thresholds have been developed for this pest, it is generally recommended that further management be considered when an average of five adelgids per shoot is observed. Yield losses have not been quantified at this density.
Prevention
Planting spruce and Douglas-fir close together should be avoided. Since both trees are usually needed to complete development, maintaining a large distance between them will disrupt the life cycle of this pest.
Cultural control
Galls can be pruned from small spruce trees before adults emerge in July. Removing old, brown galls will only improve the aesthetic appearance of the tree since adults will have already emerged.
Biological control
In the Pacific Northwest, surveys on spruce trees infested with Colley spruce gall adelgid have documented arthropod predators from nine families in the orders Hemiptera, Neuroptera, Coleoptera, and Diptera. However, other than conserving resident populations of these natural enemies, there are currently no guidelines or recommendations established for their release.
Chemical control
Control is generally not necessary, and densities of the Cooley spruce gall adelgid vary from one season to the next. To prevent the formation of galls for aesthetic purposes, insecticides can be applied in the fall or spring before eggs are laid.
Pesticides are most effective when applied before the formation of galls. This can be done in the fall or in the spring before females lay eggs in late April. Horticultural oils can also provide some protection but tend to cause temporary discoloration on spruce needles. Foliar applications of insecticidal soaps are most effective when applied to the underside of spruce terminals to target overwintering insects.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Ahren, R., D. Hawthorne, and M. Raupp. 2009. Phylogeography of a specialist insect, Adelges cooleyi: historical and contemporary processes shape the distribution of population genetic variation. Molecular Ecology. 18: 343-356. Available https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1365-294X.2008.04034.x
Childs, R., 2011. Cooley Spruce Gall Adelgid. University of Massachusetts Amherst – Center for Agriculture, Food, and the Environment. Available https://ag.umass.edu/landscape/fact-sheets/cooley-spruce-gall-adelgid
Government of Canada. 2015. Cooley spruc gall adelgid. Government of Canada. Available https://tidcf.nrcan.gc.ca/en/insects/factsheet/5307#:~:text=The%20presence%20of%20the%20Cooley,in%20the%20spring%20and%20summer
Munson, S., 2010. Cooly Spruce Gall Aphid. United States Department of Agriculture – Forest Service. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5187372.pdf
Maine Forest Service. 2000. Cooley Spruce Gall Adelgid. Maine Department of Agriculture, Conservation, and Forestry. Available https://www.maine.gov/dacf/mfs/forest_health/insects/cooley_spruce_gall_adelgid.htm
Ross, D., G. Kohler, and K. Wallin. 2017. Predators collected from balsam woolly adelgid and Cooley spruce gall adelgid in western Oregon and Washington, U.S.A., with reference to biological control of hemlock woolly adelgid (Hemiptera: Adelgidae). The Pan-Pacific Entomologist. 93(2): 56-60. Available https://bioone.org/journals/the-pan-pacific-entomologist/volume-93/issue-2/2017-93.2.56/Predators-collected-from-balsam-woolly-adelgid-and-Cooley-spruce-gall/10.3956/2017-93.2.56.full
Strong, W., and R. Bennett. 2009. Sampling plan for Adelges cooleyi (Hemiptera: Adelgidae) in spruce seed orchards. Available https://www.cambridge.org/core/services/aop-cambridge-core/content/view/E74405BE8B1EAB2A133E92113AE99DB6/S0008347X00000845a.pdf/div-class-title-sampling-plan-for-span-class-italic-adelges-cooleyi-span-hemiptera-adelgidae-in-spruce-seed-orchards-div.pdf
Swier, S., 2016. Spruce Gall Adelgid. University of New Hampshire – Extension. Available https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource002819_Rep4174.pdf
USU. (n.d.). Cooly Spruce Gall Adelgid. Utah State University – Extension. Canadian Entomologist. 142: 14-23. Available https://extension.usu.edu/pests/ipm/ornamental-pest-guide/arthopods/aphids-adelgids/cooley-spruce-gall-adelgid