UI Extension Forestry Information Series II and Diseases No 17

Balsam Woolly Adelgid Yvonne Barkley

Introduced pests have as silver fi r (Abies alba) are able to support large long been the source populations and remain relatively unharmed, of epidemic outbreaks while North American species of fi r, such as sub- of both insects and alpine fi r (), are highly susceptible diseases of forest trees. and die readily. Most mortality has been in for- Over the years the ested environments, but damage is also common trees of North America in urban areas. In other parts of the west (coastal have been besieged by Oregon and ), grand fi r (Abies gran- white pine blister rust, dis) is highly susceptible; however in Idaho, BWA gypsy moth, Dutch elm rarely causes mortality in grand fi r. Asian fi rs are disease, and chestnut intermediate in susceptibility and Douglas-fi r blight. One of these (Pseudotsuga menziesii), not being a true fi r, is not introduced species susceptible at all. of pests that has long caused mortality in the In some areas of the west, BWA is highly destruc- Balsam woolly adelgid on true fi rs of Idaho is the tive and has caused signifi cant mortality to large subalpine fi r balsam woolly adelgid tracts of native Pacifi c, grand, and subalpine fi r to (Abies lasiocarpa). ( piceae). the point that, in some areas, fi rs are slowly being Photo by David Beckman, eliminated from the ecosystem. As with many Idaho Department of Lands. Balsam woolly adelgid other pests, BWA can be found in association (BWA) was introduced with other insects and diseases attacking subal- to eastern North Amer- pine fi r. This complex includes BWA, western ica from Europe at the turn of the 20th century, balsam bark beetle, and Armillaria root rot, and is and have spread throughout the United States known as the “SAF complex”. Damage caused by and Canada. First reports of balsam woolly adel- these agents look similar from afar, and can eas- gid in the west were made around 1929. Balsam ily be confused. woolly adelgid was fi rst found in Idaho in 1983 at one urban site in Coeur d’Alene, and fi ve for- Life cycle. ested sites east of Moscow in Latah County. Since then, BWA has spread throughout much of the Balsam woolly adelgid are part of a group of state. insects that are closely related to aphids. Prob- ably the most signifi cant aspect of the balsam True fi rs are the only known hosts of BWA, with wooly adelgid’s success in North America is that a range of susceptibly. European species such the entire population of this species of pest is

Station Bulletin No. 96, Idaho Forestry Wildlife and Range Experiment Station, Moscow, ID female. Balsam woolly stage. In the non-overwintering generations, the adelgid reproduces neosistens stage can last from two to eight weeks. parthenogenetically, Following the neosistens stage are two forms that meaning there is no closely resemble adults, followed by the fi nal mating or fertiliza- adult stage of the life-cycle. This latter part of the tion; it only takes one cycle, which includes the two pre-adult and adult to form a new colony. stage, are called the sistentes. By late September, Balsam woolly adelgid has There are between the second generation of adults begins to lay eggs a white waxy covering that two and four gen- and do so as late as mid- November. looks woolly. erations of adelgids Photo by Robert L. Anderson, per growing season, Damage. USDA Forest Service. depending on locality and elevation. In the Balsam woolly mountainous areas of the west, two generations adelgid feed on the are most common. stems, branches, and twigs of their Activity begins in April when overwintering host species. Dur- nymphs begin development. These nymphs are ing feeding they about 1/32nd inches long, amber colored, fl at- inject a growth tened, and fringed with whitish wax. Nymphs Gouting. substance into the develop through three instars and mature sexu- outer bark which Photo by William M. Ciesla, Forest causes abnormal ally to begin laying eggs around June. As the Health Management International. nymphs mature to adults they produce a wax- cell division result- like covering that resembles wool. Adults and ing in swelling, or eggs are protected by this waxy, woolly layer “gouting”, of twigs and branches. Gouting ap- covering them. Adults are approximately 1/16th pears as stunting of the terminal growth as well inches long and wingless. They are purple to as distinct swellings around the buds and branch black in color under their white woolly layer and nodes. Larger and older trees or overcrowded remain attached to the tree by their deeply pen- stands are usually attacked fi rst, though all sizes etrating mouth parts for their entire adult lives. of trees are vulnerable.

Eggs begin hatching in June into active, amber- Feeding can be concen- colored crawlers, the only stage of the life-cycle trated on the stems or in which this pest is mobile. Their small size in the crowns. In the allows crawlers to travel great distances, be- West, stem attacks are ing transferred from tree to tree by wind, rain, more common on the and humans. In forest situations wind best sites and crown dispersal is thought to be the principal means of attacks more common transfer from one host tree to another. on poorer sites. BWAs can also concentrate Trunk attack. Once a crawler has found a suitable site, it sinks their attack in heavy, it’s long, sucking mouth parts into the outer bark mass infestations along Photo by Jerald E. Dewey, and begins sucking sap from the tree. Crawlers the trunk of a host tree, USDA Forest Service. transform into a fl attened, wax-fringed resting with 100 to 200 adelgids stage known as neosistens. In colder areas of per square inch of bark surface. The stems of its range this is the only stage that will survive trees under heavy attack form reddish, irregular winter temperatures and thus overwinters in this growth rings, which disrupt water conduction to

2 the crown and often results in mortality within Special thanks to Stephen Cook, Ecologist, Uni- two to three years of attack. With crown attacks, versity of Idaho and Tom Eckberg and Neal Kittelson, trees decline over a number of years and growth Lands Program Specialists – Forest Health, Idaho is slowed. Old needles drop and are not replaced Department of Lands for their extensive review of this by new ones, and cone and seed production is article. greatly reduced. For more information about BWA and SAF Com- Control. plex you can go to:

There are several USDA Forest Service Forest Insect and Disease predators of the balsam Leafl et 118: Balsam Woolly Adelgid at: woolly adelgid, includ- ing ladybird beetles, http://www.fs.fed.us/r6/nr/fi d/fi dls/fi dl-118. syrphid fl y larvae, pdf and green lacewings. Though predators are Idaho Department of Lands Management Guide often present, they have for Balsam Woolly Adelgid at: not been able to achieve http://www.fs.usda.gov/Internet/FSE_DOCU- economic levels of con- Biological control of MENTS/stelprdb5187218.pdf BWA by the trol. Systemic chemical predacious Syrphid fl y . control is feasible in This article fi rst appeared in the Farm Bureau home landscape and Gem State Producer, June, 2011, Vol. 15, Issue 4. Photo by Steven Katovich, other urban settings, USDA Forest Service. but not across large About the Author: Yvonne Barkley is an tracts of forestland. Associate Extension Forester at the University of Idaho, Moscow, ID.

Balsam woolly adelgid outbreak. Photo: Robert L. Anderson, USDA Forest Service.

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