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Balsam Woolly Adelgid

Authors:
Forest Insect
& Disease
Leaflet 118
Revised May 2006
U.S. Department of Agriculture Forest Service
Balsam Woolly Adelgid
Iral R. Ragenovich and Russel G. Mitchell
The balsam woolly adelgid, Adelges pi-
ceae (Ratzeburg), is a tiny sucking insect
that was introduced into North America
from Europe. It probably rst entered
the Northeastern United States and
Southeastern Canada around 1900. Lat-
er, it appeared on the West Coast (1929),
and in the Southeastern United States in
the mid 1950’s. Infested nursery stock is
the presumed source of introduction.
In Europe, host trees are relatively
insensitive to attack and the insect is not
considered a signicant forest pest. In
North America, however, it has caused
signicant damage and mortality to true
rs (Abies spp.) in both eastern and west-
ern forests. In some localities, rs are
slowly being eliminated from the ecosys-
tem; and adelgid populations continue to
spread to previously uninfested areas.
Hosts and Distribution
True rs are the only known hosts of the
balsam woolly adelgid. Susceptibility
ranges from highly sensitive to resistant,
with North American species being the
most sensitive to attack. European rs,
especially European silver r (Abies alba
Miller), support large adelgid popula-
tions and yet remain relatively un-
harmed. Asian rs seem intermediate in
sensitivity; some are damaged and some
are not.
Figs. 1a and 1b. Gouting caused by the
balsam woolly adelgid.
Fig. 2: Crown symptom shows crown decline and
“ddle-shape”.
2
In North America, infestations occur on
balsam r (Abies balsamea (L.) Mill.)
in the northeastern United States and
the Maritime Provinces of Canada; and
bracted balsam r (A. balsamea var.
phanerolepis Fernold) and Fraser r (A.
fraseri (Pursh) Poir.) in the mountainous
regions of Virginia, North Carolina and
Tennessee. In the West, it occurs primar-
ily on subalpine r (Abies lasiocarpa
(Hook.) Lindl), Pacic silver r (A.
amabilis (Dougl.) Forbes) and grand r
(A. grandis (Dougl.) Lindl.) in Oregon,
Washington, Idaho and British Columbia.
Subalpine r and Pacic silver r are
infested in the mountainous areas and
grand r in the lowland valleys. See
the map for the distribution of balsam
woolly adelgid in North America (pg. 6
& 7).
Several other North American r spe-
cies, such as white r (A .concolor (Gord
and Glend.)Lindl.), noble r (A. procera
Rehd.) and Shasta r (A. magnica A.
Murr) have shown signs of resistance in
natural stands, but have been reported as
being attacked by the
adelgid in exotic or off-
site plantings.
Symptoms
“Gouting” is a symptom
of balsam woolly adel-
gid attack that occurs
on North American rs.
It appears as stunting
of the terminal growth
with distinct swellings
around the buds and
branch nodes (Figures
1a and 1b). The larger
swellings occur in the
fastest growing parts of
the crown, and on trees
that have been lightly
infested for a long
time. Trees with this
kind of injury decline
slowly, often persist-
ing for years. Growth
is retarded and tree
crowns often take on a
“ddle-shaped” ap-
pearance (Figure 2) or
experience “top curl”
(Figure 3). The dead,
or dying, upper stem is
often invaded by wood-
destroying fungi.
Another, more seri-
ous,
type of attack is
Fig. 3: Crown symptom showing “top
curl”.
the mass infestation along the main bole
(Figure 4).
Populations frequently reach
densities of 100 to 200 adelgids per
square inch of bark surface. Symptoms
of decline vary somewhat with the tree
species infested, but generally the foliage
in a dying tree turns yellow, then deep
red or brown. This sequence is particu-
larly characteristic of infested balsam,
Fraser, and subalpine r.
The habits of the insect and the response
of the infested trees also appear to vary
by region. In the West, stem-infested
grand and Pacic silver rs generally
have needle loss, followed by a change
in color to a grayish-green and, ultimate-
ly, death. These trees often die quickly,
sometimes after only 2 or 3 years of
heavy infestation. Symptoms of gouting
are seldom conspicuous in conjunction
with stem infestations because of the
trees’ weakened condition and the short
period of infestation before tree death.
In the Northeast, both gouting and stem
attacks can be seen on the same tree, and
trees with stem attacks can often survive
for a decade or more.
All sizes of trees are attacked, although
trees that are pole-sized or larger seem
most susceptible. In the West, stem
infections are most abundant on the best
sites, and crown attacks occur more
often on poorer sites. In the Maritime
Provinces of Canada, it appears that
stem infestations are more abundant in
the inland areas and crown attacks occur
more often on the coastal areas. In New
England, there does not appear to be a
geographic pattern to the occurrence of
the gout phase or the stem infestation.
Bracted rs generally have gout infesta-
tions and Fraser r has primarily sus-
tained stem attacks.
Fig. 4: Heavy stem infestion of balsam
woolly adelgid along the stem of sub-al-
pine r.
3
Effect on Host Trees
Stem and twig injury is a result of the
insect feeding on the host. The adelgid
injects a substance into the bark that ap-
parently affects the hormonal reaction of
the tree and causes abnormal cell division
and differentiation in the bark and newly
formed wood. Giant parenchyma cells
develop in the bark, and the cambium is
stimulated to produce an abnormal number
of phloem and ray cells. At the same time,
an abnormally wide annual ring composed
of cells with unusually thick walls is pro-
duced in the woody tissue.
On twigs and branches, the abnormal cells
cause a swelling, or gouting, at the nodes.
These trees may live for many years, but
growth is curtailed. Slowly, old needles
drop and are not replaced by new ones.
Cone and seed production is considerably
reduced.
Fig. 5: Compression-like wood in irregular
outer rings caused by the trees reaction to
feeding by the balsam woolly adelgid.
Reddish, irregular growth rings, similar to
compression wood, referred to as “rotholz”
in the literature, occur in the stems of the
trees that have heavy bole attacks (Figure
5). This disrupts water conduction to the
crown and often results in tree death within
2-3 years after the attack.
Fig. 6: Ventral view of balsam woolly
adelgid.
Life History and Behavior
Balsam woolly adelgid populations in
North America are composed entirely
of females; as a result, reproduction is
parthenogenetic (i.e. without mating and
fertilization). Adults are tiny (about 1mm.
long) dark purple to black, nearly spheri-
cal and wingless (Figure 6). They produce
a thick mass of a waxy wool-like mate-
rial that covers the body and protects the
adult and her eggs (Figure 7). Some 100
- 250 amber colored eggs are laid under
this wool-like coat. An amber colored
crawler hatches from the egg. The newly
hatched crawler is the only stage capable
of directed movement or dispersal. Long
range spread is accomplished mainly by
wind, although contact with birds and other
animals may also contribute to natural dis-
persion. The crawler disperses and seeks
a feeding site – most often bark lenticels
and other roughened areas of the main
stem, around branch and twig nodes, and
the base of buds in the crown. It inserts its
mouthparts into the bark and transforms,
without molting into a attened wax-
fringed resting stage known as neosistens.
In the mountains, the neosistens is the only
stage that will survive winter temperatures.
Two immature forms closely resembling
4
the adult follow the neosistens. These
two forms, plus the adult are called the
sistentes.
A rare stage, known as the progrediens has
been observed in Europe and the Mari-
time Provinces of Canada. In one form,
it is wingless and in another, winged.
The wingless form is very similar to the
sistentes. The winged form has membra-
nous wings, ve-segmented antennae, and
generally lack wax pores.
and early October, and egg laying continues
until about mid- November.
In some areas where temperatures are
warmer and there are extended warm sea-
sons, additional generations can occur. A
partial third generation usually develops in
North Carolina, and three generations with
a partial fourth occur in the lowland areas
of Oregon and Washington.
Likewise, the extended months of colder
Fig. 7: Balsam woolly adelgid eggs and crawler. Wool pushed aside for
photographic purposes.
The balsam woolly adelgid has 2 to 4 gen-
erations per year, depending on locality and
elevation. Two generations are most com-
mon in mountainous areas of the West and
throughout New England and the Maritime
Provinces of the East. Spring development
begins in late April or early May; by the
end of June, most are in the adult stage.
This is followed by an egg-laying period
of about 6 weeks. In warm weather, eggs
hatch within a few days, and the crawlers
settle on the bark and transform into the
resting, neosistens stage, which lasts from 2
to 8 weeks. Adults of the second genera-
tion become abundant in late September
winter temperatures and the shortened
season of warmer temperatures that char-
acterize some of the higher elevations,
especially in the northern latitudes, can
either result in fewer generations per year,
or possibly limit the distribution of the
adelgid entirely.
Effects and Impacts
In initial, intense infestations, when the
adelgid rst colonizes a stand, it encoun-
ters a reservoir of susceptible trees that has
accumulated over many years. Since all
adelgids are females, all individuals have
the ability to reproduce, and population
5
increases are exponential. These factors
result in considerable spectacular tree mor-
tality for several years (Figures 8a, 8b, and
8c), and are characterized by stem attacks.
After the initial wave of tree mortality,
the effects of the adelgid become rather
unspectacular because host is limited,
populations uctuate, it takes time for new
trees to grow into a susceptible state, and
environmental factors exert an inuence
on lower populations. It appears that once
the adelgid colonizes a stand, it is there
Range of balsam woolly adelgid infestation in North America.
8c
8a
6
Extensive tree mortality
from balsam woolly
adelgid following initial
infestation.
Fig. 8a: Individual tree
mortality and fading
trees.
Fig. 8b: Extensive tree
mortality.
Fig. 8c: Older mortality
with scattered dying
trees.
8b
Range of balsam woolly adelgid infestation in North America.
permanently, and mortality continues on
individual trees many years after the initial
infestation.
In areas where site, host, and environ-
mental factors are not conducive to large
population increases, chronic low-level
infestations occur. These are more often
characterized by gouting. New growth is
halted in the crown, and cone and seed pro-
duction is curtailed. These infestations can
kill trees over time and decline is usually
evidenced through varying degrees of top
kill, poor crowns, and reduced reproduc-
tion (Figure 9). Trees that are weakened
and have a poor live-crown ratio are more
susceptible to the effects and impacts of
other insects and disease agents. For ex-
ample, moderate defoliation from western
spruce budworm may result in signi-
cantly more mortality in stands infested
by balsam woolly adelgid, than would be
expected to occur in an uninfested stand.
Although it is unlikely that the balsam
woolly adelgid will eliminate its hosts en-
tirely, it does present some local ecological
problems. In harsh or disturbed environ-
ments, such as old lava ows, avalanche
tracks and marshy meadows, subalpine r
acts as a pioneer species. By killing trees
and inhibiting cone production, the balsam
woolly adelgid has removed the subalpine
r from some of these local areas. In the
lower Willamette Valley in Oregon, and the
Puget Sound Trough in Washington State,
long-time infestations in the bark cracks
and along branches of large old grand rs,
have gradually destroyed crown char-
acteristics, cone crops are rare, and new
reproduction is non-existent. As a result,
grand r is slowly disappearing from these
ecosystems. In the East, balsam r repro-
duction within infested r stands is very
good. However, much of the regeneration
is heavily infested with the gout phase, and
the future of that regeneration is uncertain.
Fig. 9: Gradual tree decline evidenced
through varying degrees of poor crowns,
top kill and eventual mortality.
7
In areas where host is limited or conned,
such as the Fraser r on scattered moun-
tain- tops in the Appalachians, signicant
initial mature tree mortality occurred; how-
ever, Fraser r regeneration is extensive
(Figures 10a and 10 b). Stand character-
istics have been changed, by changing the
patterns of age and distribution of the r.
The effect of balsam woolly adelgid on
this regeneration as it matures, remains to
be seen, and it is possible that successive
cycles of regeneration-mortality will result
in decreasing numbers of trees over time.
Photo by William Ciesla
Photo by William Ciesla
Figs. 10a and 10b: Fraser r second-growth following extensive mature tree mortality
from balsam woolly adelgid on Mt. Mitchell in North Carolina.
8
Management and Control
Natural Predators and Parasites
No parasites of the balsam woolly adelgid
are known, but many predaceous enemies
have been observed. Most North American
predacious insects or spiders are general
feeders and unreliable as control factors.
They do not seem to concentrate on adel-
gid populations or uctuate with adelgid
population levels.
Several species of insect predators have
been introduced into North America from
other parts of the world, primarily Europe.
These include 3 beetles - Laricobius erich-
sonii (Rosenhauer) (Derondontidae); Pul-
lus impexus (Mulsant) (Coccinellidae), and
Aphidecta obliterata (L.) (Coccinellidae);
and 3 ies - Aphidoletes thompsoni Mohn
(Cecidomyiidae), Cremifania nigrocellula-
ta (Czerny) (Chamaemyiidae), and Leuco-
pis obscura Haliday (Chamaemyiidae). As
yet, none of these predators have affected
any detectable level of adelgid population
control. They appear to feed on stages of
the adelgid that are unimportant in deter-
mining trends in the adelgid populations.
In initial stages of infestation, expanding
adelgid populations increase so rapidly,
and some tree species are so sensitive to
attack, that predators have little chance of
affecting any control before irreversible
damage has been done.
Environmental and Cultural Management
The populations and effects of the adelgid
may be limited on individual trees by the
response of the tree itself. Stem-attacked
trees that survive more than 1 or 2 years
may form patches of a wound layer in
bark that is still living, but impermeable
to insect attack. Over time the adelgid
populations are increasingly restricted to
a smaller and smaller area until most adel-
gids die. Eventually, though, because the
tree continues to grow and the protective
layer becomes cracked, the tree is subject
to re-infestation.
Weather is also an important factor in af-
fecting insect survival, particularly in the
northern latitudes and higher elevations.
In cold winters, only adelgids below the
snowline will survive temperatures of be-
low 30 degrees F. Subalpine rs growing
close to timberline may not be as affected
as trees at a lower elevation, because dur-
ing short spring and summer seasons there
is rarely enough heat accumulation for the
insects to complete a second generation
and allow good winter survival (only the
resting 1st instar can survive the winter in
the mountains).
Stand and host susceptibility also appear
to be related to other environmental fac-
tors such as elevation, stand age, and site
condition. Some hosts such as grand r are
susceptible at low elevations, but rarely
attacked at higher elevations. Pacic silver
r and subalpine r also experience severe
infestations at low elevations. At higher
elevations subalpine r experiences heavy
infestations, but adjacent Pacic silver r
is rarely attacked. Mature Fraser r is very
susceptible, while younger trees do not ap-
pear to be as affected in natural conditions,
but can be heavily infested in plantations.
Species such as noble and red rs, that
are resistant under natural conditions, can
be attacked when planted in off-site and
ornamental situations.
The combination of host, site, and other
environmental factors makes this a dif-
cult insect to manage. For some tree
species, reducing stocking and improving
site conditions may reduce susceptibil-
ity; however, with other species, good site
conditions make a species more susceptible
to this insect. Hazard/Risk rating systems
using site variables such as elevation, soil
and site conditions, and stand conditions,
developed for each individual tree species,
can help identify those instances where a
particular species would be most suscep-
tible, and those situations where other
species may survive. Where possible, the
land manger should select against suscep-
tible or infested individuals and favor more
tolerant, or non-host species, either through
selection harvest or planting.
9
In Christmas tree plantations or other high-
value situations removing infested trees
(if there are only a few individuals) and/or
direct control can reduce the impact of the
balsam woolly adelgid.
Direct Control
The adelgids are hidden in protective nich-
es of the bark and branches of trees and
are individually protected by their wool-
like waxy exudation. Applying contact
insecticides effectively by aerial spraying
over large areas is not possible. However,
spraying individual trees from the ground
with an approved insecticide has proved
effective for control.
Contact insecticides are most effective
against the exposed crawler stage and are
applied as a bark drench with a hydraulic
sprayer in May through June and Septem-
ber through October. Some of the insecti-
cidal soaps and oils can penetrate the waxy
coating of the adult adelgids, however,
timing of application is important, in order
to avoid burning the foliage on the tree.
Treatment will reduce populations to be-
low the tree-killing level, and some treated
trees may remain generally free from
adelgids for several years.
Spraying is warranted only in accessible
areas supporting relatively high-value
trees. Some systemic insecticides are reg-
istered for adelgid control and may be ef-
fective on balsam woolly adelgid. Contact
local extension agents or forest entomol-
ogy experts for the currently registered and
most effective insecticides.
References
Amman, Gene D. 1962. Seasonal biology
of the balsam woolly aphid on Mt. Mitch-
ell, North Carolina. J. Econ. Entomol.
55(1):96-98.
Amman, G.D. and Charles F. Speers. 1965.
Balsam woolly aphid in the southern Ap-
palachians. J. Forest. 63:18-20.
Amman, Gene D. and Robert L. Talerico.
1967. Symptoms of infestation by the
balsam woolly aphid displayed by Fraser
r and bracted balsam r. USDA Forest
Serv. Southeast. Forest Exp. Sta. Res. Note
SE-85. 7p.
Balch, R.E. 1952. Studies of the balsam
woolly aphid, Adelges picea (Ratz) and its
effects on balsam r, Abies balsamea (L.)
Mill. Can. Dept. Agric. Pub. 867. 76p.
Carroll, W. J. and D. G. Bryant. 1960. A
review of the balsam woolly aphid in New-
foundland. Forest. Chron. 36:278-290.
Foulger, A. N. 1968. Effect of aphid in-
festation on properties of grand r. Forest
Prod. J. 18(1):43-47.
Johnson, Norman E., Russell [Russel] G.
Mitchell, and Kenneth H. Wright. 1963.
Mortality and damage to Pacic silver r
by the balsam woolly aphid in southwest-
ern Washington. J. Forest. 61: 854 - 860.
Livingston, R. L.; J. E. Dewey; D. P. Beck-
man, and L. E. Stipe. 2000. Distribution of
the balsam woolly adelgid in Idaho. West.
J. of Applied Forest. 15(4):227-231.
Mitchell, Russel G. 1966. Infestation char-
acteristics of the balsam woolly aphid in
the Pacic Northwest. USDA Forest Serv.
Pacic Northwest Forest and Range Exp.
Sta. Res. Pap. PNW-35. 18p.
Mitchell, Russel G. and Paul E. Buffam.
2001. Patterns of long-term balsam woolly
adelgid infestations and effects in Oregon
and Washington. West. J. of Applied For-
est. 16(3): 121-126.
Mitchell, Russel G., Norman E. Johnson,
and Julius A. Rudinsky. 1961. Seasonal
history of the balsam woolly aphid in the
Pacic Northwest. Can. Entomol. 93:
794-798.
Mitchell, R. G. and K. H. Wright. 1967.
Foreign predator introductions for control
10
of the balsam woolly aphid in the Pacic
Northwest. J. Econ. Entomol. 60(1): 140-
147.
Smith, George F. and N. S. Nicholas.
2000. Size- and age-class distributions of
Fraser r following balsam woolly adelgid
infestation. Can. J. For/. Res. 30: 948-
957.
Turnquist, R. and J. W. E. Harris. 1993.
Balsam woolly adelgid. Can. Forest. Serv.
Forest Pest Leaet. 4p.
Witter, John A. and Iral R. Ragenovich.
1986. Regeneration of Fraser r at Mt.
Mitchell, North Carolina, after depreda-
tions by the balsam woolly adelgid. Forest
Sci. 32 (3): 585 – 594.
Acknowledgements
Map: Information provided by: Nelson
Carter - Canadian Forest Service, James
Linnane - USDA Forest Service Northeast-
ern Area, and Dave Trotter - British Co-
lumbia Ministry of Forests. Map produced
by Sundi Sigrist - USDA Forest Service.
Photos: Figures 1a, 2, 3, 4 and 5 - Oregon
Department of Forestry. Figures 1b, 6,
7, 8b and 9 - Washington Department
of Natural Resources. Figures 3 and 8c
- USDA Forest Service. Figure 8a - Idaho
Department of Lands. Figures 10a and 10b
- William Ciesla.
Review: Kyle Lombard, New Hampshire
Division of Forests and Lands, David
Overhulser, Oregon Department of For-
estry
11
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R6-NR-FID-PR-04-2006
... Due to these structural changes, both the phloem (due to wound periderm formation) and xylem (due to rotholz formation) become non-translocating, resulting in a state of physiological drought within the tree (Hain et al. 1991). Continued infestation by BWA can reduce bud production (Ragenovich and Mitchell 2006) and inhibit photosynthesis (see Hain et al. 1991), leading to crown and tree mortality (Balch 1952). ...
... However, the relationship between gouting by BWA and fir foliar chemistry remains unstudied. Although BWA gout does not directly affect foliage, reductions in bud production (Ragenovich and Mitchell 2006) and reduced translocation through branches (Hain et al. 1991) likely affect resource allocation and foliar chemical composition and therefore may affect the performance of subsequent herbivores who feed on that foliage. ...
... As shown in previous studies (Balch 1952;Ragenovich and Mitchell 2006), bud production and shoot elongation were reduced on gouted branches, suggesting that these branches allocated fewer resources to growth than did ungouted branches (Chapin 1991;Arendt 1997). By inhibiting bud production, BWA alters both crown architecture and source-sink relationships within the tree (Ho 1988) and may themselves act as additional sinks by diverting resources from nearby buds (Larson and Whitman 1997;Miller-Pierce et al. 2010), while simultaneously hindering nutrient flow to distally located buds by slowing translocation through gouted nodes (Balch 1952). ...
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The balsam woolly adelgid (Adelges piceae) is a gout-inducing hemipteran native to the silver fir forests of Europe. Introduced to eastern North America approximately 100 years ago, it is now found in most balsam fir forests in Atlantic Canada. When A. piceae feed, they trigger a reaction in the host branch that alters both xylem and phloem morphology. We conducted a field survey to examine the relationship between A. piceae gout density and balsam fir foliar chemistry and shoot growth in naturally unthinned and precommercially thinned stands. A. piceae gout density negatively affected branch growth and was related to changes in the chemistry of older, but not current-year foliage. Older foliage experienced decreases in camphene and bornyl acetate, while foliar concentrations of camphene, myrcene, phenolics, potassium and water differed between thinned and unthinned stands. Foliar chemistry was also influenced by interactions between thinning and A. piceae gout density in old foliage. This study suggests that changes in balsam fir associated with A. piceae gout density may force native defoliators that feed in highly gouted trees to adapt to diets of different chemical compositions and that thinning may alter these interactions.
... Two additional stressors have contributed to the decline of swamp forests, particularly those with a Balsam Fir component. Adelges piceae Ratzeburg (Balsam Woolly Adelgid) is an invasive species introduced from Europe around 1900 (Ragenovich and Mitchell 2006). It constitutes a serious threat to both Abies fraseri (Pursh) Poir. ...
... (Fraser Fir) and Balsam Fir in the eastern US. The insect attacks trees of all sizes, although seed-bearing and mature overstory trees appear to be most susceptible (Ragenovich and Mitchell 2006). Although we did not document the degree of infestation, we observed that many firs showed evidence of being attacked or killed by Balsam Woolly Adelgid. ...
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... While even large populations of A. piceae need not greatly impact their native host, European silver fir [Abies alba (Mill.)] (Balch, 1952; Ragenovich and Mitchell, 2006), North American Abies spp. show a hypersensitive reaction when fed upon by this adelgid. ...
... These visible effects are accompanied by exaggerated cell growth in the bark and cambium, inhibition of bud production, and reduced photosynthetic capacity (Balch, 1952). Thickening of cell walls and reductions in tracheid pit apertures disrupt water conduction to the crown of the tree (Balch, 1952; Ragenovich and Mitchell, 2006). Severe and continued gout can cause branch, crown and even tree mortality (Balch, 1952), but shorter-term effects are felt as well: A. piceae attack alters branch growth and chemistry of one-to-four-year-old balsam fir foliage (Grégoire et al., 2014). ...
... This may be due to the presence of suitable host species for these pests at these locations or the proximity to initial introductions. Balsam woolly adelgid likely was introduced in the early 1900s to southeastern Canada (Ragenovich and Mitchell, 2006). According to the IDS data we presented here, balsam woolly adelgid had a more severe effect on coastal balsam fir (Abies balsamea) forests in ME than other fir-dominated locations, probably due to the high percentage of fir located there and proximity to the initial introduction. ...
... lasiocarpa) in California, Oregon, Washington and British Columbia [10,11,12,13,14,15,16]. Today the insect continues to disperse eastward and northward across Idaho, western Montana and British Columbia [17,18,19,20,21] where it is causing significant damage to subalpine fir stands. BWA is anticipated to continue to spread throughout the range of subalpine fir and cause significant decline of this important high elevation species. ...
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... Balsam woolly adelgid, Adelges piceae (Homoptera: Adelgidae), is an exotic species that infests both the main stem and branches of true firs (Fig. 56) and is established in fir forests in both the eastern and western US (Ragenovich and Mitchell 2006). ...
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