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Balsam Woolly Adelgid

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
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.
“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-
type of attack is
Fig. 3: Crown symptom showing “top
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.
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
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
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
the adult follow the neosistens. These
two forms, plus the adult are called the
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
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.
Extensive tree mortality
from balsam woolly
adelgid following initial
Fig. 8a: Individual tree
mortality and fading
Fig. 8b: Extensive tree
Fig. 8c: Older mortality
with scattered dying
Range of balsam woolly adelgid infestation in North America.
permanently, and mortality continues on
individual trees many years after the initial
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.
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.
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.
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.
Amman, Gene D. 1962. Seasonal biology
of the balsam woolly aphid on Mt. Mitch-
ell, North Carolina. J. Econ. Entomol.
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:
Mitchell, R. G. and K. H. Wright. 1967.
Foreign predator introductions for control
of the balsam woolly aphid in the Pacic
Northwest. J. Econ. Entomol. 60(1): 140-
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-
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.
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-
Pesticides used improperly can be injurious to humans,
animals, and plants. Follow directions and read all
precautions on the labels. Consult your local forest
pathologist, county agricultural agent, or State extension
agent about restrictions and registered uses of particular
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... 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). ...
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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Abes Run wetland is a biologically diverse, 82-ac (33-ha) complex of wet meadow, marsh, scrub-shrub, and forested-swamp communities in Canaan Valley, WV. In 2002, we sampled the vegetation in six 65-ft (20-m)-wide transects and identified a total of 179 vascular plant species. We classified 23 species as introduced; 38 occurred at or near the southernmost known limit of their range. Two graminoid-dominated (e.g., Carex spp. [sedges], Leersia spp. [cutgrass], and Scirpus spp. [bulrush]) and forb-dominated (Euthamia spp. [goldenrods]) transects occurred in an area that had been forested and later inundated by Castor canadensis (North American Beaver) in the 1970s. Four transects were mixed-deciduous and coniferous forested-swamp communities. With the exception of transect 5, these sites had an organic horizon that was 32-40-in (80-100-cm) deep in the center, and the water table tended to persist at the wetland surface through the first half of the growing season. The tree stratum was well-developed, although discontinuous, and was dominated by mixtures of Fraxinus nigra (Black Ash), Abies balsamea (Balsam Fir), Picea rubens (Red Spruce), and Betula alleghaniensis (Yellow Birch). A rich shrub layer of Rhamnus alnifolia (Alder-leaved Buckthorn), Ilex verticillata (Winterberry), and Alnus incana ssp. rugosa (Speckled Alder) was also present. The broken overstory created a variable light regime on the wetland floor and as a consequence, there was high diversity of herbaceous plants. Although a rank comparison of 1945 vs. 1997 vegetative-cover classes did not yield any significant differences, we noted 3 trends: 1) North American Beaver activities reduced the area of coniferous swamp forests, 2) wet-graminoid areas increased as beaver dams were abandoned and their impoundments dried, and 3) the extent of scrub-shrub communities increased, particularly in the upper portions of the wetland's drainage.
... 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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The balsam woolly adelgid (Adelges piceae (Ratzeburg) (Homoptera: Adelgidae)) (BWA) is a nonnative, invasive insect that threatens Abies species throughout North America. It is well established in the Pacific Northwest, but continues to move eastward through Idaho and into Montana and potentially threatens subalpine fir to the south in the central and southern Rocky Mountains. We developed a climatic risk model and map that predicts BWA impacts to subalpine fir using a two-step process. Using 30-year monthly climate normals from sites with quantitatively derived BWA damage severity index values, we built a regression model that significantly explained insect damage. The sites were grouped into two distinct damage categories (high damage and mortality versus little or no mortality and low damage) and the model estimates for each group were used to designate distinct value ranges for four climatic risk categories: minimal, low, moderate, and high. We then calculated model estimates for each cell of a 4-kilometer resolution climate raster and mapped the risk categories over the entire range of subalpine fir in the western United States. The spatial variation of risk classes indicates a gradient of climatic susceptibility generally decreasing from the Olympic Peninsula in Washington and the Cascade Range in Oregon and Washington moving eastward, with the exception of some high risk areas in northern Idaho and western Montana. There is also a pattern of decreasing climatic susceptibility from north to south in the Rocky Mountains. Our study provides an initial step for modeling the relationship between climate and BWA damage severity across the range of subalpine fir. We showed that September minimum temperature and a metric calculated as the maximum May temperature divided by total May precipitation were the best climatic predictors of BWA severity. Although winter cold temperatures and summer heat have been shown to influence BWA impacts in other locations, these variables were not as predictive as spring and fall conditions in the Pacific Northwest.
... 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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Pest damage is a general problem that disturbs the growth of forests, influencing carbon sequestration and causing economic losses. In the past decades, many studies have been conducted to monitor and detect forest insect damage using satellite remote sensing technology. Satellite remote sensing has a satellite or aerial vision allowing the monitoring of extensive forest areas, but it usually requires constant time periods and is prone to cloud interference. To enable more efficient and effective monitoring of forest pest damage, a video-based monitoring framework is presented. This framework comprises three key parts: (1) video positioning of forest insect damage based on digital elevation model (DEM) and the parameters obtained from the pan-tilt-zoom camera, (2) integration of two-dimensional/three-dimensional geographic information system and video surveillance to provide more intuitionistic monitoring and assistance for positioning, (3) on-site verification conducted by ground surveys and guided through global positioning system (GPS) integrated in the embedded devices. The experiment was carried out over two forest areas to validate the proposed method. Results showed that the framework bears a sound positioning accuracy and high detection ratio, which could be effectively used in detecting and monitoring forest insect defoliation and discoloration. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.
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Invasive arthropod species cause ever-increasing economic, environmental and public health problems. Microbes (i.e. viruses, bacteria, fungi, nematodes and protists) have been used very successfully for eradicating and controlling a range of invasive arthropods in diverse ecosystems worldwide. Many eradication and control programs using microbes have used inundative augmentation (widespread application) approaches while some control programs have instead focused on classical biological control (point release and natural spread). This chapter provides a short history of past use of microbes for control of invasive arthropods as well as an introduction to the subjects that will be covered in this book.
The balsam woolly aphid, Adelges piceae (Ratz.), first recorded in Newfoundland in 1949, is now the most serious forest insect pest in the Province, having spread over an area of more than 1,600 square miles. Its host is balsam fir, Abies balsamea (L.) Mill. There are three separate infestations, the largest and most important being in southwestern Newfoundland. The aphid has two generations a year. A biological control program was initiated in 1952 and seven species of predators have been released, three of which are established. Silvicultural and climatic control factors are discussed and the possibilities for the extension of outbreaks are considered.
The balsam woolly aphid, Chermes ( Adelges ) piceae Ratz., is widely distributed in Europe and North America. It infests many species of Abies (true firs) and may be found attacking its hosts at elevations from near sea level to timberline (5,000 to 6,000 feet). Because of the great range of environments inhabited by the balsam woolly aphid, its biology differs considerably from one region to another. Perhaps the most variable feature in its biology is seasonal history. Karafiat and Franz (1956) reported three generations per year in central Europe, whereas Varty (1956) noted two and sometimes a partial third generation in Scotland. Balch (1952) found only two generations in the Maritime Provinces of Canada, but Amman noted three and sometimes a partial fourth generation in southeastern United States.
Fraser fir (Abies fraseri (Pursh) Poir.) has suffered catastrophic mortality throughout most of its native range from an exotic insect, the balsam woolly adelgid (Adelges piceae Ratz.). To assess the regeneration potential and viability of fir populations, overstory and understory Fraser fir size and age structure were analyzed. The data were collected from thirty-six 400-m(2) permanent plots, stratified into four stand canopy composition types, established near the summits of five mountains in the Great Smoky Mountains. We found that, where canopy mortality was severe, fir advance regeneration was re-entering the overstory. In seriously impacted stands, mortality of large fir and increased recruitment have produced distributions characterized by few large fir and relatively high densities of small fir. Densities of 0- to 10-year-old fir seedlings and fir seedlings less than or equal to 0.25 m tall were much lower in stands dominated by dead fir than in mostly intact fir stands. While the lack of reproducing adults appears to be the main cause, competition with invasive species and higher seedling mortality from environmental factors probably contribute. These results lead to a hypothesis that Fraser fir will undergo a regeneration-mortality cycle with a decrease in the numbers of each successive generation.
The balsam woolly aphid (Chermes piceae Ratz.) was shown to be a serious pest of Pacific silver fir (Abies amabilis [Dougl.] Forbes) in the Pacific Northwest. The degree of damage was greatest on dominant and co-dominant trees growing on the best sites. The relative site index was related to the number of trees with stem infestations which in turn was related to the percent of dead trees in the stand and the general crown condition. Recommendations are given for minimizing losses from this important forest pest by the use of a penalty rating system.
The balsam woolly aphid, Adelges piceae (Ratzeburg), an import from Europe, causes major damage to true fir forests in North America. A program has been underway since 1957 to control the pest in Oregon and Washington by introducing insect predators. Twenty-three species have been introduced from 7 countries throughout the world. They include 15 species of beetles, 4 of flies, 3 of lacewings, and I bug. Three species of flies, Aphidoletes thompsoni Möhn, Cremifania nigrocellulata Czerny, and Leucopis obscura Haliday and 2 species of beetles, Laricobius erichsonii Rosenhauer and Pullus impexus (Mulsant), are successfully established. They prey on the aphid but so far have not sufficiently reduced populations to prevent tree killing. Reasons for their failure include poor synchronization of predator-prey seasonal habits, inadequate searching ability of the predators, and inability of the host trees to withstand even light populations of the aphid. Search for more effective predators is continuing. The aphid problem is expected to decrease as the present virgin old forests are converted, under management, to less susceptible young forests. Aphid predators may become relatively more effective under such forest conditions.
Studies of the seasonal biology of the balsam woolly aphid, Chermes piceae Ratzeburg (Adelgidae: Homoptera), were carried out in 1960 following discovery of a severe infestation of this insect on Mt. Mitchell. Observations of aphid development were made in the field on 3- by 3-inch plots of bark on living trees. In addition, microscopic counts of aphids on bark samples were made at frequent intervals in the laboratory. Observations within the plots revealed as many as three generations per year, Data obtained from bark samples showed that most of the aphid population completed two generations.
The balsam woolly adelgid (Adelges piceae) is an introduced pest discovered damaging grand fir (Abies grandis) in Oregon's Willamette Valley around 1930. In 1955, the insect was found infesting and killing Pacific silver fir (A. amabilis) near Mt. St. Helens in Washington and subalpine fir (A. lasiocarpa) in the Cascade Range in Oregon. In the next 10 yr, the pest dispersed widely throughout western Oregon and Washington, causing significant tree mortality over thousands of acres in the Cascade Range. Observations on trend plots established 35 to 40 yr ago have shown somewhat consistent trends in the patterns of infestation and damage. Infestations and damage were most severe on the best sites and at the lowest elevations where the hosts grow. Tree damage was consistently most severe in the first decade of infestation, but the insect never seemed to disappear from a stand; infestations and tree killing were observed on some plots 40 yr after the initial infestation. An ecological problem with the balsam woolly adelgid is a pattern of attack that is gradually eliminating grand fir from low-elevation landscapes west of the Cascade Range. The adelgid is also removing subalpine fir as a pioneer tree species in many of the important mountain environments. West. J. Appl. For. 16(3):121–126.
The balsam woolly adelgid (Adelges piceae) was introduced from Europe to northeastern North America in about 1900. In 1983, it was discovered infesting fir trees in Idaho. Since then, aerial and ground surveys have documented its spread in Idaho over an area of approximately 14,000 mi 2 (8,960,000 ac). It now covers most of the central one-third of the state. Aerial surveys in 1997 and 1998 identified about 125,000 ac of host type with dead or damaged trees. Subalpine fir (Abies lasiocarpa) is a critical species in many high elevation areas. The effects of the balsam wooly adelgid on aesthetics, hydrology, and other ecological values can be very important. The adelgid is likely to continue its spread throughout subalpine fir forests of Idaho and neighboring states. West. J. Appl. For. 15(4):227-231,
Fraser fir, in the Southern Appalachians, is being rapidly killed by the balsam woolly aphid. The completion of the Blue Ridge Parkway will open a direct route from infested areas to all remaining uninfested fir areas in North Carolina. Trees are killed when activity of the aphid causes them to produce annual growth rings of compression-like wood. Death of Fraser fir rapidly follows 2 to 5 years of aphid infestation on the bole. Aphids in selected areas and on specimen trees can be controlled for at least two years with a single hydraulic application of 1/8-percent benzene hexachloride water emulsion. Four species of predators obtained from Europe show promise in control.