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Introduction
The Hemlock Woolly Adelgid (Adelges tsugae) is an exotic pest insect that
has invaded the Southern Appalachians over the last few years. Because this
species can kill host hemlock trees within 4 years of infecting them
(McClure, 1987), it now looms as an environmental disaster of regional
magnitude. Hemlocks are currently an integral component of the Southern
Appalachian mountain ecosystem. The most shade tolerant tree species in
North America (Quimby, 1996), hemlocks provide unique ecosystem services
and habitat for numerous species (Yamasaki et al. 2000). Their beauty is
valued at campgrounds, trails, vistas, and homesteads through the region.
However, within a decade most of the region's two hemlock species, Eastern
Hemlock (Tsuga canadensis) and Carolina Hemlock (Tsuga caroliniana), could
be dead.
Exotic pests can be extremely detrimental to native species.
The introduced Chestnut Blight (Cryphonectria parasitica)
eliminated an estimated 3 billion mature American Chestnut trees throughout
eastern North America in the 1920's. Another invasive exotic,
the Balsam Woolly Adelgid (Adelges piceae) killed mountainsides of Frasier Firs
in the Southern Appalachians in the 1960's.
Similarly, Hemlock Woolly Adelgid threatens to have a massive negative impact on the region's forests and,
in turn, outdoor recreation and tourism.
Since their introduction into Virginia in the 1950's (Souto et al. 1996), these adelgids have taken
a heavy toll. They have killed approximately 75% of the hemlocks in
Shenandoah National Park, Virginia, for example (Akerson and Hunt 1998).
In the Great Smoky Mountain National Park scientists have only recently
begun to inventory the diversity of species associated with hemlock forests
(Johnson et. al. 2000). Just as we begin to understand the complexities
and workings of hemlock forests, we risk losing them.
The Hemlock Woolly Adelgid (A. tsugae) is a tiny, aphid-like insect native to
Japan. A small piercing and sucking insect, A. tsugae feeds on sap in young
twigs and branches, typically near the point of needle attachment (Young et
al. 1995). The result is needle loss, which in turn prevents trees from
producing new growth (McClure, 2003). Because A. tsugae attacks trees at the
base of individual needles, all ages and sizes of eastern hemlock trees are
susceptible to damage. In contrast to the minimal affect A. tsugae has had
on western hemlock species, it severely defoliates and kills Eastern
Hemlock (T. canadensis) and Carolina Hemlock (T. caroliniana) in the
East.
Given the regional scale and short time-line remaining, it may already be
too late to save many of the region's hemlocks. A stop-gap solution is to
protect the most valuable hemlocks with insecticides. However, such
treatment is expensive and needs to be repeated periodically to counter
reinfection. The patchy distribution of eastern hemlock (Quimby, 1996) and
its association with riparian areas (Williams and Moriarity, 2000) make
chemical controls in forested areas impractical (McClure, 1987). Studies
in Connecticut, North Carolina, and Virginia identified several native or
established predators associated with the A. tsugae, yet they
were found at densities too low to significantly impact A. tsugae populations
(Zilahi-Balogh et al. 2003). Long-term hope rests on biological
control--establishing natural enemies that will regulate adelgid
populations at levels not lethal to the hemlocks. Several non-native beetle
species feed on adelgids, and hence, are potential biological control
agents (Cheah and McClure, 1998; McClure et al., 2000; Zilahi-Balogh,
2001). Currently two species of beetles Pseudoscymnus tsugae and
Laricobius nigrinus have been released as biological controls. A third
beetle, Scymnus ningshanensis is being examined as a candidate for release
(Montgomery et al. 2000).
Objectives
Here we propose research to answer two critical questions:
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In a Southern Appalachian climate, are the reproductive and
consumption rates of P. tsugae sufficiently high, relative to
the adelgids intrinsic life history parameters, to regulate the pest? If
the answer to this question is no, then while P. tsugae may slow the
adelgid infestation, it is not a long-term solution.
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Can volunteers rear P. tsugae beetles in sleeves on infected trees
more cost effectively than laboratory reared beetles, which currently cost
$2 - $3 each? If the answer to this question is yes, we will disseminate
information so that volunteers can be trained to help rear and release
these beetles.
Materials and Methods
The proposed project will measure the reproductive and consumption rates of
P. tsugae beetles in the field under various adelgid prey densities. In so
doing, it will also determine whether these beetles can be reared efficiently on
sleeved branches of infected trees.
The project will be conducted in the following stages:
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Pre-experiment -- finding and recording the density of adelgid populations on study branches (March-April)
While the adelgids are easy to find and count during their winter "woolly"
stage, they are difficult to find after their eggs hatch and they become
small crawlers. As a consequence, they are difficult to work with during
the summer months and relatively little is known about their reproductive
and survival rates during this time. Hence, this March and April, with the
help of volunteers, we propose to find at least 200 trees at the Highlands
Biological Station and vicinity that range in their level of adelgid
infection from light to heavy. We will record the density of adult adelgids
on 5 branches on each of these trees. We will geo-reference the trees and
individually mark the branches.
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Experiment-1 -- measuring impact of beetles on adelgids by
manipulating beetle densities on these branches using sleeves and suitable
controls (May-July)
This experiment requires three branches per tree of those surveyed in
March-April. Starting in May, after crawlers have hatched, we will put two
1 meter sleeves on each tree. We will select branches with similar adelgid density within
a tree, but different densities across trees. We will
then randomly assign sleeves to "experimental" and "control" treatments. We
will put a male and a female P. tsugae beetle into the experimental
sleeves. We will not put beetles into the control sleeves. We will close
ninety percent of sleeves, enclosing the beetles and adelgids until the end
of the experiment. To control for the effect of sleeves, we will leave ten
percent of them open at their terminal end. In addition, we will use one
unsleeved branch per tree as an additional control. In some of the
sleeves, we will allow the beetles to exit into a vial after a varying
number of days. Thus, they will not be in the sleeves all summer and will only feed and lay eggs
for a specific amount of time.
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Experiment-2 -- measuring beetle reproductive rates in sleeves with different adelgid densities (May-July)
This experiment requires the two remaining branches per tree of those
surveyed in March-April. Its goal is to measure beetle reproductive rates
under different rearing conditions and adelgid densities. In May we will
enclose a pair of beetles in a sleeved branch. After sufficient time to
allow for a generation of beetles, which will be on the order of 4 - 6
weeks depending on temperature, we will harvest the branch and count how
many beetles were produced. In July, we will start to repeat the same
experiment on the remaining branch. In addition to measuring beetle
reproduction as a function of adelgid density, we will try to find ways to
optimize beetle production. To do this we will vary conditions for the
beetle and the time that they are trapped in the sleeves. For example, we
will put a honey source in some sleeves to see if it increases beetle
survival and reproduction. In others, we will allow the beetles to exit
into a vial after a certain number of days, thus allowing them to lay eggs
and move on as they would if wild. In this way, we hope to avoid
cannibalism that is known to occur when beetle larval density is high.
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Post-experiment -- recording the density of beetles and adelgids on experimental and control branches (October+)
At the end of the summer season, after the adelgids have formed woolly
balls that are easy to count, we will re-survey the three branches used in
Experiment-1 and determine their impact on the adelgids as a function of
adelgid density.
Significance of the proposed project
It is not known whether the released P. tsugae or L.
nigrinus beetles are capable of establishing and regulating adelgid
populations in the Southern Appalachian environment. Given the limited
quantities of beetles that are being produced by existing rearing
facilities, it is doubtful that sufficient numbers of them will be
available to provide protection before it is too late. If there is any hope
for biological control to occur rapidly, we need to muster an army of
volunteers to help study the adelgids and their natural enemies, monitor
and map their distributions, and rear and release beetles in vast numbers.
In the next year, grassroots support, technology, and research must all
come together to harness the energy and resources of enough people to
tackle the adelgids at a scale that has any chance of success. Fortunately,
grassroots support for saving the hemlocks is very strong. In addition to
federal and state agencies, there are numerous local and regional
organizations that are concerned about the problem and who will help find
volunteers and coordinate their activity. These include Balsam Mountain
Trust, Chatooga Conservancy, Georgia Forest Watch, Highlands Biological
Station, Jackson-Macon Conservation Association, Southern Appalachian Man
and the Biosphere Program (SAMAB), and Western North Carolina Alliance. In
addition, email and new Web technology will empower us to coordinate large
numbers of volunteers and allow them to integrate geo-spatial information
into on-line databases and real-time maps. In partnership with
Topozone.com, Discover Life (http://www.discoverlife.org) will provide
maps, aerial photographs, and software tools so that Web users can report,
database, and map their findings about Hemlock Woolly Adelgids.
The research proposed here will help determine if P. tsugae
is an effective biological control agent. It will also find out whether
rearing these beetles in sleeves is possible and cost effective.
Previous work done on the project
Kok and Salom (2002) have begun to explore the use of field insectaries to
rear hemlock woolly adelgid predators in Virginia. Although this method of
rearing is not as labor intensive as laboratory rearing and exposes insects
to more natural conditions, Kok and Salom's project involves the planting
of a hemlock stand and infection of that stand. Sleeve cage studies of
Scymnus sinuanodulus and P. tsugae have been conducted by the
USDA Forest Service research laboratory in Hamden, Connecticut to determine
their impact potential on A. tsugae densities (Blumenthal 2002b). There was no
mention of a control group in this study, only sleeves containing beetles
were examined. Sleeve cage studies in 2001 preformed in Pennsylvania
confirmed that P. tsugae continued to feed and breed throughout
the spring and summer, producing new generations of predators for the
following year (Blumenthal, 2002a). Currently there is no research
addressing sleeve cage studies in the southern Appalachians.
Statement as to whether the proposed project will be supported by other agencies
No. Some private support available.
Literature cited
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Akerson, J., and G. Hunt. 1998. HWA status at Shenandoah National Park.
Hemlock Woolly Adelgid Newsletter #3: 10-11. (USDA Forest Service).
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Battles, J.J., N. Cleavitt, T.J. Fahey, and R.A. Evans. 2000. Vegetation
composition and structure in two hemlock stands threatened by hemlock
woolly adelgid. In: Proceedings of a Symposium on Sustainable Management of
Hemlock Ecosystems in Eastern North America, edited by K.A. McManus, K.S.
Shields, and D.R. Souto. pp. 55-61.
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Blumenthal, E.M. 2002a.
Report:
Pseudoscymnus tsugae in Pennsylvania Forests. Proceedings: Hemlock
Woolly Adelgid in the Eastern United States Symposium. February 5-7, 2002.
East Brunswick, New Jersey. pp. 166-169.
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Blumenthal. E.M. 2002b. Forest insect biological control. Forest Pest
Management Newsletter- PA DCNR. June 2002.
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Cheah, C.A. S-J. and M.S. McClure. Life history and development of
Pseudoscymnus tsugae (Coleoptera: Coccinellidae), a new predator of the
hemlock woolly adelgid, Adelges tsugae (Homoptera: Adelgidae). Environ.
Entomol. 27: 1531-1536.
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Johnson, K.D., F.P. Hain, K.S. Johnson, and F. Hastings. 2000. Hemlock
resources at risk in the Great Smoky Mountains National Park. In:
Proceedings of a Symposium on Sustainable Management of Hemlock Ecosystems
in Eastern North America, edited by K.A. McManus, K.S. Shields, and D.R.
Souto. pp.111-112.
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Kok, L.T., S.M Salom. 2002. Possible Use of Field Insectaries to Rear
Hemlock Woolly Adelgid Predators. Department of Entomology, Virginia
Polytechnic Institute and State University. Blacksburg VA.
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McClure, M.S. 1987. Biology and control of hemlock woolly adelgid.
Connecticut Agricultural Experiment Station Bulletin 851, pp. 3-9.
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McClure, M.S. 1991a. Density-dependent feedback and population cycles in
Adelges tsugae (Homoptera: Adelgidae) on Tsuga canadensis. Environmental
Entomology (20) 1: 258-264.
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McClure, M.S., C.A.S.-J. Cheah and T.C. Tinger, 2000. Is Pseudoscymnus
tsugae the solution to the hemlock woolly adelgid problem?: an early
perspective. In: K.A. McManus, K.S. Sheilds and D.R. Souto (eds),
Proceedings, Symposium on Sustainable Management of Hemlock Ecosystems in
Eastern North America. June 22-24, 1999, Durham, NH. USDA Forest Service,
General Technical Report NE-267. pp. 89-96.
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McClure, M.S., S.M. Salom, and K.S. Shields, 2003. Hemlock Woolly
Adelgid. FHTET-2001-03. Morgantown, WV:USDA Forest Service. 1p.
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Montgomery, M.E., D. Yao, and H. Wang. 2000. Chinese Coccinellidae for
biological control of the hemlock woolly adelgid: Description of native
habitat, pp. 97-102. Proceedings, Symposium on Sustainable Management of
Hemlock Ecosystems in Eastern North America. June 22-24, 1999, Durham, NH.
USDA Forest Service, Newtown square, Pennsylvania.
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Quimby, J. 1996. Value and importance of hemlock ecosystems in the United
States. In: S.M. Salom, T.C. Tigner, and R.C. Reardon, eds. Proceedings of
the First Hemlock Woolly Adelgid Review, Charlottsville, VA, 1995. USDA
Forest Service Forest Health Technology Enterprise Team-Morgantown, WV.
FHTET 96-10. pp. 1-8.
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Snyder, C., J. Young, D. Smith, D. Lemarie, R. Ross, and R. Bennett. 1998.
Influence of eastern hemlock decline on aquatic biodiversity of Delaware
Water Gap National Recreation Area. Final Report to the National Park
Service.
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Souto, D., T. Luther, and R. Chianese. 1996. Past and current status of HWA
in easter and Carolina hemlock stands. In: S.M. Salom, T.C. Tigner, and
R.C. Reardon, eds. Proceedings of the First Hemlock Woolly Adelgid Review,
Charlottsville, VA, 1995. USDA Forest Service Forest Health Technology
Enterprise Team-Morgantown, WV. FHTET 96-10. pp. 9-15.
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Williams, C.E. and W.J. Moriarity, 2000. Composition and structure of
hemlock-dominated riparian forests of the northern Allegheny Plateau: a
baseline assessment. In: K.A. McManus, K.S. Shields, and D.R. Souto (eds),
Proceedings, Symposium on Sustainable Management of Hemlock Ecosystems in
Eastern North America. June 22-24, 1999, Durham, NH. USDA Forest Service,
General Technical Report NE-267. pp. 216-224.
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Yamasaki, M., R.M. DeGraaf, and J.W. Lanier. 2000. Wildlife habitat
associations in eastern hemlock - birds, smaller mammals, and forest
carnivores. In: Proceedings of a Symposium on Sustainable Management of
Hemlock Ecosystems in Eastern North America, edited by K.A. McManus, K.S.
Shields, and D.R. Souto. pp.135-141.
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Young, R.F., K.S. Shields, and Berlyn. 1995. Hemlock woolly adelgid
(Homoptera: Adelgidae):stylet bundle insertion and feeding sites. Annals
of the Entomological Society of America. 88:827-835.
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Zilahi-Balogh, G.M.G., 2001. Biology of Laricobius nigrinus Fender
(Coleoptera: Derodontidae) and its potential as a biological control agent
of the hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae)
in the eastern United States. PhD dissertation. Virginia Polytechnic
Institute and State University, Blacksburg, VA. 108 pp.
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Zilahi-Balogh, G.M.G., S. M. Salom, and L. T. Kok. 2003. Development and
reproductive biology of Laricobius nigrinus, a potential biological control
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Short biographical sketch including publications
Molly Nicholie is a 1995 graduate of Warren Wilson College, with a degree
in Environmental Science. Since graduating she has worked as an Americorps
volunteer and a classroom teacher. As a certified arborist Molly has
diagnosed and treated hemlock woolly adelgid infestations in landscape
situations. She became involved in ecology as a field technician working
at an LTER station in Puerto Rico. She has since gone on to help examine
the nesting success of birds in hemlock vs. hardwood-dominated forests in
the Great Smoky Mountains National Park.
Type of laboratory facilities needed and list of equipment that you wish the Station to provide
The project will need access to the insectary/growth chambers for short term storage
of beetles, a dissecting microscope, and computer access.
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