Balsam woolly adelgid (BWA) is an invasive insect from central Europe that feeds on all true fir trees (Abies spp.). This insect inserts its straw-like mouthparts into the trunk or branches of trees and feeds on the nutrient rich sap. It also injects toxic saliva into the tree which causes abnormal wood formation that disrupts the flow of water and nutrients throughout the tree. Swelling in the branches can lead to branch dieback and successive years of infestation may cause tree mortality. Severe stem infestations can cause tree mortality in two to three years.
Balsam woolly adelgid (BWA) has two generations per year and only females have been observed in North America, meaning reproduction is asexual. Adult BWA are very small (0.5-1.0 mm long), dark purple to black, oblong, and wingless. Female adults secrete a white, waxy substance that covers their body and eggs for protection. The wax is visible on the bark of host trees. Adult BWA are present and laying eggs in late spring. By early summer the eggs hatch into reddish-brown crawlers which is the only mobile life stage.
Crawlers disperse to new feeding sites on the same tree, or are transported by wind or animal to a new host tree. Once the crawlers begin feeding, they remain stationary and continue development into adults. Adults are again present and laying eggs in late summer and early fall. Eggs hatch and crawlers disperse to new feeding sites in late fall. Once these crawlers begin feeding they enter into their overwintering stage called neosistens. In early spring, the neosistens continue their development into the adult stage and most BWA are adults by late spring.
Balsam woolly adelgid is native to central Europe and was first detected in North America around 1900. The United States first observed BWA in New England, but by the 1930s, it had been transported to the Pacific Northwest.
The only mobile life stage of BWA are the crawlers looking for new feeding sites or hosts. These crawlers are transported to other fir trees by wind or animals that brush against infested trees. Long distance transportation can occur through the movement of infested trees or wood.
Since its initial detection in New England and northeast Canada, BWA has slowly been spreading throughout the United States. It is now present in at least 16 states including: Maine, New Hampshire, Vermont, New York, North Carolina, Virginia, West Virginia, Tennessee, California, Washington, Oregon, Idaho, Montana, Utah, Alaska, and Michigan.
Extensive research on BWA biology, effects and impacts, and management and control options has been done to date. The USDA, state governments, and universities are currently researching BWA in new environments, such as Utah where it was first discovered in 2017, as well as best silvicultural practices for managing infested trees. Detection surveys are performed regularly to monitor current infestations and scout for new ones.
Local governments are also providing outreach and education programs to teach property owners about identifying and managing BWA infestations. Currently, the only state in the U.S. with an active quarantine restricting the movement of true fir species is Michigan.
Early Balsam Woolly Adelgid:
Management options for:
Homeowners should scout their fir trees regularly for signs of BWA infestation. If BWA is discovered, report findings to your state government or local extension office. To prevent spread of BWA, consider removing and destroying any infested trees. This should be done in the winter, when the crawler stage is not present, to prevent accidental spreading. If a desirable tree becomes infested, chemical control is an option for individual trees. Contact pesticides can be applied while crawlers are present, in May through June and September through October. Some insecticidal soaps and oils may go through the waxy coating of the adults, but will be more effective against the crawler stage.
Adult BWA can live for a few months after trees are removed, therefore trees should be destroyed on site and firewood should never be moved.
There are currently no effective, large scale BWA control methods. In infested stands, BWA can be managed with silviculture by strategic thinning and planting or selecting for resistant or non-host species. Harvesting infested trees should take place in the winter, when crawlers are not present to prevent accidental spreading. To protect high value individuals, contact pesticides can be applied while crawlers are present in May through June and September through October.
Michigan is the only U.S. state with BWA quarantine in place. This exterior quarantine prohibits the entry into Michigan of any living form of BWA and any true fir (Abies spp.) tree as nursery stock or forest products.