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Invasion of
the Asian Longhorned Beetle Anoplophora glabripennis (Coleoptera:
Cerambycidae): A Canadian Focus
Published: March 17, 2010;
1(7): 35-37
Keywords: Anoplophora
glabripennis; Invasive
Species, Life Cycle; Native Range; Urban Forests
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The
Asian longhorned beetle (Anoplophora
glabripennis) is a large, wood-boring invasive insect species
native to China and Southeastern Asia that preys upon healthy
hardwood trees, as well as trees under stress, by tunneling through
their vascular system and depriving them of vital nutrients, leading
eventually to their death. Since its discovery in the mid-1990s and
early-2000s in the United States and Canada, respectively,
government officials have been actively involved in preventing the
further spread of this pest by screening cargo and surveying
high-risk sites (Bell, 2004). Unfortunately, the only effective
treatment to recover an Asian longhorned beetle-infested region is
to cut down infested trees and destroy the wood. This has led to the
removal of tens of thousands of infested urban trees
in an
effort
to eradicate this exotic pest
(Nowak
et al., 2001).
In fact, it has been predicted that if the
A.
glabripennis
outbreak were to become
widespread, it would significantly impact forests across North
America, with an
estimated death toll of 1.2 billion trees (.
A. glabripennis
is believed to have been accidentally introduced from China to North
America in untreated solid wood packing material, such as wooden
crates, sometime during the early-1990s. It was first discovered to
have colonized and infested trees in the United States along the
coast of New York State, in 1996 (Peterson
et al., 2004). In 1998, a
growing population of A.
glabripennis was detected in the Chicago, Illinois area (Nowak
et al., 2001), and a
third location infested with this species was identified in Jersey
City, New Jersey, in 2002 (MacLeod
et al., 2002). More
recently, the Canadian Food Inspection Agency confirmed the presence
of this exotic species in the Woodbridge area of Southern Ontario in
2003 – although probably present since at least 1998 (Bell, 2004).
Since dispersal distances for beetles are relatively short – average
of 106.3 metres (Wen et al.,
1998) – it is believed that the infestations discovered in New York
State and New Jersey spread from the same point of entry, whereas
the infestations in
Chicago and Woodbridge originated from separate points of entry.
Spread by human activity can also accelerates dispersal, especially
if packing material or firewood infested with eggs, larvae, and
pupae are shipped without proper inspection or chemical treatment
(Nowak et al., 2001).
Unfortunately, estimates on the introduction date in Ontario predate
the regulations enacted to prevent the movement of untreated wood
from Hong Kong and China (Bell, 2004).
Although various life stages of the beetle have been detected by
alert workers in warehouses (Nowak
et al., 2001), no other
established A. glabripennis
populations have been detected in the United States and Canada.
The
number of annual generations of
A. glabripennis varies
with climate and latitude (EPPO, 1998). That is, the further North A.
glabripennis is found, the longer it takes for a generation to
develop. For instance, in Taiwan, one generation occurs per year,
whereas in Northern China, a single generation takes two years to
develop (MacLeod et al.,
2002). Similarly, in Ontario,
A. glabripennis has a one to two year life cycle. Adult beetles
generally emerge in July and August, while some have been found as
early as June 26th in New York (Nowak
et al., 2001), and live
for about a month to as late as mid-autumn (EPPO, 1998). In
contrast, adult beetle emergence in Southern China begins in early
spring, and in late June and July farther North (Nowak
et al., 2001). This
period also underlies when adult beetles are most active,
especially during the heat of the day. The adults typically show a
strong preference to lay eggs in the host-tree from which they
emerged or fly relatively short distances to another host, where
they feed on leaves, petiole, and the bark of young new shoots, when
the population density becomes too high in their original host
(MacLeod et al., 2002).
After mating, the Adult female
A.
glabripennis
chews out oval or round grooves, known as ovipositing sites, into
the main trunk, branches, and exposed tree roots, where eggs are
laid a week after
copulation (MacLeod et al.,
2002). An adult can chew up to 35 to 90 individual depressions and
lay up to 25 to 40 eggs per generation. The eggs, which are about 5
to 7mm long, are laid one by one under the bark, with each egg
occupying a single oviposition slit (EPPO, 1998). The slits are
typically cut on the Eastern side of the trunk or of branches
greater than 5cm in diameter (MacLeod
et al., 2002). Within a
two-week period, larvae of A.
glabripennis hatch from their oviposition niche and immediately
bore into the wood, creating a visible scar on the surface of the
bark. The larvae possess an off-white body colour and brown
mandibles, with a segmented body that can reach a size of up to
60mm. Early instar larvae feed in the phloem and the primary xylem
layers of the branches and trunk and later enter the woody central
part of the secondary xylem known as heartwood tissue (EPPO, 1998).
Disruption of the cambium-phloem interface reduces nutrient and
water transport within the tree, whereas the destruction of sapwood
or heartwood tissue caused by later instar larvae, severely weakens
the trees’ structure and stability (Kreutzweiser
et al., 2008). Generally,
larvae of A. glabripennis
feed in more than 24 species of hardwood trees (Nowak
et al., 2001; MacLeod
et al., 2002). In its
native China and South Eastern Asia, including Taiwan, Korea, and
parts of Japan, it prefers species of willows and species of
cottonwood, whereas in the United States and Canada, species of
maple are most commonly attacked (MacLeod
et al., 2002). Other
hardwoods species, including poplar, birch, horse chestnut, elm, and
several new hosts have been documented in North America (Nowak
et al., 2001).
Pupation of mature larvae takes place in chambers at the end of the
feeding tunnel within the heartwood. The pupae hatch into adults
over the winter months and chew their way out of the tree, leaving
large circular holes, 10mm across, above the sites where the eggs
were initially laid, accompanied by large amounts of sawdust-like
wood shavings and animal waste, known as frass, packed into the
chamber or around the base of the tree. In contrast to adult female
A. glabripennis, male
beetles are significantly smaller in size and can be seen anywhere
on the tree as they rest or wander in search of a mate. Adult male
A. glabripennis are
typically 25 mm long, while adult females are 35 mm long. The
antennas are 2.5 times the body length in males and 1.3 times the
body length in females – giving rise to this beetle’s common name –
and have 11 segments, each with a whitish-blue base. The beetle is
glossy black with about 20 irregularly-shaped white spots scattered
along its wings (EPPO, 1998).
A. glabripennis
is one of the most serious pests
in China, causing substantial economic damage to poplars throughout
the country (Macleod et al.,
2002). Since larvae tunnel deep into the tree, killing this pest
with biological or chemical pesticides remains a challenge. Like
many exotic species, A.
glabripennis has no known natural predators in North America
that can control its spread. Recent studies, however, have shown a
particular insecticide, known as imidaclorid, to be quite effective
against beetles, especially when applied though soil and trunk
injections (Wang et al.,
2001). Insecticide treatment by soil injection under host trees has
commenced in Ontario (Bell, 2004) and Chicago (Nowak
et al., 2001). However,
neurotoxic pesticides are harmful agents that are likely to cause
unforeseen problems to indigenous species living on trees or within
the soil and to waterways if used on trees alongside riparian zones.
This measure only provides control, rather than eradication. Other
control options currently being adopted include (Macleod
et al., 2002): (i)
Complete felling and destruction of infested trees to reduce
population size and prevent spread; (ii) the use of chemical
insecticides that prevent adults from laying eggs on the surface of
the bark or sprays that kill adults directly; (iii) the use of trap
trees to capture adult beetles and prevent them from laying eggs on
specific surveyed trees; and (iv) planting trees that are more
tolerant to A. glabripennis
invasion.
Since more than 50 percent of Toronto’s urban trees are maple,
infested trees pose the threat of personal injury and property
damage that can result from tree breakage where beetles have
weakened stems and branches (Nowak
et al., 2001). These
trees and others threatened provide the city it aesthetic appeal,
protection from the sun, fresh oxygen, and habitats for wildlife,
such as birds and mammals. Thus, the removal of street and parkland
trees in urbanized areas will likely cause a reduction in property
value (Macleod et al.,
2002). Furthermore, if A.
glabripennis were to expand and go unchecked beyond current
quarantined urban areas, the Canadian forest-based economy, which
generates more than $30 billion in wood products annually (Forest
Industry in Canada, 2009), would inevitably falter and collapse.
Similarly, the maple syrup industry, which generates another $213
million each year, would also be impacted (Maple Syrup Industry in
Canada, 2008). Broad-leaved deciduous trees are a vital component of
healthy woodlands in Southern Canada. An uncontrolled population
growth of A. glabripennis
would not only affect tourism and recreation to which healthy
forests support, but it would also overwhelm forest health and
biodiversity. In Ontario, the number of trees removed after the
first outbreak was 11000+ trees (Bell, 2004). Likewise, since the
discovery of the infestations in 1996, damage from infestations in
the United States has resulted in the removal of 30000+ trees and
cost to State and Federal governments in excess of $269 million
(Macleod et al., 2002).
Due
to the Asian longhorned beetle’s
obscure lifestyle and tendency to lay a relatively low number of
eggs on several different host species (Macleod
et al., 2002), prospects
for early detection and successful eradication of infested sites are
reduced. However, if appropriate awareness is raised to the public,
early detection of infestations by community members will likely
decrease the spread of this invasive species. Henceforth, the full
cooperation of the general public is required if eradication
programs are to succeed (Asian Longhorned Beetle, 2007).
References
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Asian longhorned beetle (Anoplophora glabripennis).
Natural Resources Canada.
Retrieved February 18, 2010, from: http://cfs.nrcan.gc.ca/subsite/glfc-sugarbush/anoplophora-glabripennis.
EPPO:
European and Mediterranian Plant Protection Organization. (1998).
EPPO Data Sheets n Quarantine Pests:
Anoplophora glabripennis.
OEPP/EPPO Bulletin, 29:
497-501.
Forest
Industry in Canada. (2009). Economic Benefits and Forest Products:
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D.P., Good, K.P., & Chartrand, D.T. (2008). Are Leaves that Fall
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