Database Reference
In-Depth Information
(0.00, 0.4), (400000, 0.4), (800000, 0.375), (1.2e
+
06, 0.345), (1.6e
+
06, 0.33),
(2e
+
06, 0.315), (2.4e
+
06, 0.285), (2.8e
+
06, 0.26), (3.2e
+
06, 0.235),
(3.6e
+
06, 0.21), (4e
+
06, 0.18)
11.3 Wolly Adelgid
11.3.1 Infestation of Fraser Fir
Fraser fir populations have been decimated in the Mt. Mitchell area of Yancey
County, North Carolina by the Balsam woolly adelgid,
Adelges piceae
. Fraser fir is
a high altitude fir native to North America.
A. piceae
was introduced from Europe.
Since its first detection in 1959, it has been responsible for the loss of over 2 million
trees. Most impacted sites have been unable to recover fully.
A. piceae
is an external
feeder on bark and new growth spirals. This feeding causes abnormal growth, even-
tually killing trees and adversely impacting the timber industry. A mature Fraser fir
is estimated to support 50,000 A. piceae. Once this critical level is achieved, death
of the tree is inevitable within two years. Death of a tree results in the loss of the
pests on that tree from the entire park population.
In an attempt to prolong the life of the Fraser fir populations, 20 mature Fraser
fir trees were moved from their natural habitat on Mt. Mitchell to a nearby city
park on Grandfather Mountain, North Carolina. The city park will act as a botanic
zoo producing a viable seed bank and maintaining genetic diversity in the Fraser
fir. Unknowingly, a population of
Adelges piceae
was moved to the city park along
with the Fraser fir. Unchecked, these insects may decimate the small population of
Fraser fir moved to the park as part of a conservation measure.
Since the pest insect and host plant are now located in a city setting as opposed
to a forest habitat, the options for control are much greater. However, the public
perception of pesticide use in the city may make its use questionable politically.
Considering the cost already invested to the Fraser fir conservation program, it is of
great importance to preserve this city park population of Fraser fir. Using the model
of
Adelges piceae
population dynamics and other associated model parameters, how
does an uncontrolled population of
Adelges piceae
affect the
Fraser fir
population?
When should pesticides be applied to ensure the greatest control over the pest pop-
ulation? How do varying levels of pesticide control affect the
Adelges piceae
and
Fraser fir
populations?
11.3.2 Adelgid and Fir Dynamics
The basis of this model is the population dynamics of the pest,
A. piceae,
modeled
mathematically by
2
. The backbone of these dynamics is shown in Figures 11.17
2
Dale, V.H., R. H. Gardner, and D.L. DeAngelis. 1991. Elevation-mediated effects of balsam
woolly adelgid on southern Appalachian spruce-fir forests. Can. J. For. Res. 21: 1639-1648.
