Insects - BWA

Balsam woolly adelgid (Adelges piceae (Ratzeburg))

DESCRIPTION: All stages of the balsam woolly adelgid (hereafter BWA) are small, 1 mm or less in length, requiring a hand lens to see well. The adults are wingless and covered with a white, waxy covering that can be seen with the naked eye, but the presence of the insect under the waxy covering must still be confirmed with a hand lens. The BWA has an unusual life cycle. In the United States, all individuals are females. The adult females lay eggs that are genetically identical to herself. These eggs hatch within a month to produce the mobile crawler stage. This is the only stage which can move on the tree or be blown to adjacent tree. Once the crawler finds a suitable feeding site, the feeding tube is inserted into the bark of the tree and the insect never moves from that spot. The crawler molts in place to the nymph, and finally to the adult. There are two to three generations every year. The BWA overwinters as the nymph. (9)

INTRODUCTION HISTORY AND DISTRIBUTION: Introduced into Brunswick, Maine in 1908, the balsam woolly adelgid first appeared in the southern Appalachian Mountains in the 1950's. The pest has also found its way into the Pacific Northwest. Native to central Europe, the BWA is now distributed throughout eastern and western North America. It attacks all true firs of the Abies genus, including balsam and Fraser fir. (10)

IMPACTS ON ECOSYSTEM: BWA is the most damaging pest of balsam and Fraser fir, as well as the most difficult to control. Vast stands of trees have been killed throughout much of these species' range in the East. Damage to subalpine fir, Pacific Silver fir and Grand fir is most severe in the states of Washington and Oregon. Exotic species of true fir used as ornamentals are also subject to attack. (11) The narrowly endemic Fraser fir -- found only on the highest peaks in Great Smoky Mountains National Park and neighboring parts of North Carolina and Tennessee -- has been virtually eliminated. On one peak in Great Smoky Mountains National Park, Fraser fir -- formerly 80% of living crown trees – has virtually disappeared. The formerly closed canopy has been replaced by an open canopy, with changes in understory vegetation. These changes have caused a 35% decrease in breeding bird populations. The U.S. Fish and Wildlife Service has listed two species under the Endangered Species Act because of damage to their habitat caused by death of Fraser fir -- the spruce-fir moss spider and the rock gnome lichen. (12)

Although not a direct cause of tree mortality, feeding by the balsam woolly adelgid causes gout, a syndrome characterized by enlarged nodes and buds. When feeding begins, the adelgid injects a saliva into the tree to facilitate uptake of materials. This substance is toxic to cell tissues. A type of wood with greatly thickened cell walls forms at the attack sites and interferes with translocation of water and nutrients, thus starving the tree. The damage symptoms listed above render the wood brittle and with excessive resin content. This lowers its value as a lumber and pulping species. BWA is especially damaging to the Fraser fir Christmas tree industry. Mortality of stands causes early harvesting which disrupts planned harvesting schedules and leads to lost profits. (9, 10) Damage is usually minimal until the tree reaches maturity at about 30 years. Decline after three decades is far short of the tree's normal life span of about 150 years. Firs usually have an opportunity to produce one or two seed crops before succumbing to severe decline and ultimately mortality. This reproduction ensures the maintenance of the fir component in the forest but greatly reduces the age structure. Red spruce, immune to attack from the BWA, will make up a greater part of the spruce-fir forest type as future ecosystem structure develops. (10)

CONTROL EFFORTS: Though BWA spreads slowly, it often goes undetected for a year or more as tree symptoms may not appear for more than 6 months after trees are first infested. Many Christmas tree growers have chosen to spray a preventive insecticide on a regular basis to be "safe rather than sorry." However, a BWA treatment can cost $300 to $500 per acre and can create future problems with the spruce spider mite because of the effects to its natural predators. (9) BWA has few natural predators; some experimental biological control is underway but the effectiveness is unknown. (11)



	Insects - Balsam Woolly Adelgid

Home Overview of Invasives Case studies in US forest ecosystems Insects BWA Gypsy moth Plants Tree of heaven Kudzu Pathogens Chestnut blight Dutch elm disease Long-term effects on forests Conclusions References Useful links	*Balsam woolly adelgid (Adelges piceae* (Ratzeburg)) DESCRIPTION: All stages of the balsam woolly adelgid (hereafter BWA) are small, 1 mm or less in length, requiring a hand lens to see well. The adults are wingless and covered with a white, waxy covering that can be seen with the naked eye, but the presence of the insect under the waxy covering must still be confirmed with a hand lens. The BWA has an unusual life cycle. In the United States, all individuals are females. The adult females lay eggs that are genetically identical to herself. These eggs hatch within a month to produce the mobile crawler stage. This is the only stage which can move on the tree or be blown to adjacent tree. Once the crawler finds a suitable feeding site, the feeding tube is inserted into the bark of the tree and the insect never moves from that spot. The crawler molts in place to the nymph, and finally to the adult. There are two to three generations every year. The BWA overwinters as the nymph. (9) INTRODUCTION HISTORY AND DISTRIBUTION: Introduced into Brunswick, Maine in 1908, the balsam woolly adelgid first appeared in the southern Appalachian Mountains in the 1950's. The pest has also found its way into the Pacific Northwest. Native to central Europe, the BWA is now distributed throughout eastern and western North America. It attacks all true firs of the Abies genus, including balsam and Fraser fir. (10) IMPACTS ON ECOSYSTEM: BWA is the most damaging pest of balsam and Fraser fir, as well as the most difficult to control. Vast stands of trees have been killed throughout much of these species' range in the East. Damage to subalpine fir, Pacific Silver fir and Grand fir is most severe in the states of Washington and Oregon. Exotic species of true fir used as ornamentals are also subject to attack. (11) The narrowly endemic Fraser fir -- found only on the highest peaks in Great Smoky Mountains National Park and neighboring parts of North Carolina and Tennessee -- has been virtually eliminated. On one peak in Great Smoky Mountains National Park, Fraser fir -- formerly 80% of living crown trees – has virtually disappeared. The formerly closed canopy has been replaced by an open canopy, with changes in understory vegetation. These changes have caused a 35% decrease in breeding bird populations. The U.S. Fish and Wildlife Service has listed two species under the Endangered Species Act because of damage to their habitat caused by death of Fraser fir -- the spruce-fir moss spider and the rock gnome lichen. (12) Although not a direct cause of tree mortality, feeding by the balsam woolly adelgid causes gout, a syndrome characterized by enlarged nodes and buds. When feeding begins, the adelgid injects a saliva into the tree to facilitate uptake of materials. This substance is toxic to cell tissues. A type of wood with greatly thickened cell walls forms at the attack sites and interferes with translocation of water and nutrients, thus starving the tree. The damage symptoms listed above render the wood brittle and with excessive resin content. This lowers its value as a lumber and pulping species. BWA is especially damaging to the Fraser fir Christmas tree industry. Mortality of stands causes early harvesting which disrupts planned harvesting schedules and leads to lost profits. (9, 10) Damage is usually minimal until the tree reaches maturity at about 30 years. Decline after three decades is far short of the tree's normal life span of about 150 years. Firs usually have an opportunity to produce one or two seed crops before succumbing to severe decline and ultimately mortality. This reproduction ensures the maintenance of the fir component in the forest but greatly reduces the age structure. Red spruce, immune to attack from the BWA, will make up a greater part of the spruce-fir forest type as future ecosystem structure develops. (10) CONTROL EFFORTS: Though BWA spreads slowly, it often goes undetected for a year or more as tree symptoms may not appear for more than 6 months after trees are first infested. Many Christmas tree growers have chosen to spray a preventive insecticide on a regular basis to be "safe rather than sorry." However, a BWA treatment can cost $300 to $500 per acre and can create future problems with the spruce spider mite because of the effects to its natural predators. (9) BWA has few natural predators; some experimental biological control is underway but the effectiveness is unknown. (11)**

Insects - Balsam Woolly Adelgid