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Can pheromones and host volatiles induce Monochamus species (Cerambycidae: Lamiinae) to colonize healthy shortleaf pines?

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Abstract

Monochamus carolinensis and Monochamus titillator are large wood-boring beetles which are commonly associated with dead or dying pine trees in the southeastern United States in abundant numbers. While studies have traditionally classified Monochamus as secondary insect pests several reports have placed Monochamus species as primary pests in other geographical areas. Our objectives are to test the ability of Monochamus to attack and colonize apparently healthy pine trees and to evaluate the role of attack rate in overcoming tree defenses. A total of 24 trees were divided among four plots of mixed pine forest in two Forest Service management areas in the Ozark Mountains of Arkansas. Lures containing Monochamus aggregation pheromones and ethanol were placed 6-7 meters from the ground on the bole of healthy shortleaf pine trees. Twelve trees were treated with lures during each of two Monochamus flight periods of the year. Trees were visited biweekly to assess overall tree health and count oviposition pits. Trees will be felled and destructively sampled to determine the success of colonization by Monochamus. We predict two possible outcomes: tree defenses successfully inhibiting the development and survival of Monochamus within the tree or Monochamus successfully overcoming tree defenses, fully developing, and most likely killing the tree. Determining the ability of Monochamus to colonize healthy pines adds to our knowledge base of this ecologically significant forest insect.
Can pheromones and host volatiles induce
Monochamus species (Cerambycidae: Lamiinae) to
colonize healthy shortleaf pines?
Matthew Ethington1, Larry Galligan1, David Wakarchuk2, and Fred Stephen1
1Department of Entomology, University of Arkansas, Fayetteville, AR
2Synergy Semiochemicals Corp., Burnaby, BC
Introduction
Beetles in the genus Monochamus (Coleoptera: Cerambycidae) are large
wood-boring insects that develop primarily in pine trees (Figure 1). These
beetles are economically significant as sources of wood degradation in
lumber mills resulting in lower lumber quality. The adult beetles also
vector Bursaphelenchus xylophilus nematodes which cause pine wilt disease
in conifers exotic to the Western Hemisphere and has caused widespread
pine mortality in Asia (Linit 1988). Monochamus are ecologically important
decomposers of pines and also function as competitors and intraguild
predators of bark beetle larvae (Dodds et.al.2001,Stephen 2011).
Objective
To determine whether M. titillator and M. carolinensis will oviposit and
successfully colonize healthy shortleaf pine (Pinus echinata) when attracted by
the sex-pheromone Monochamol as well as tree volatiles and bark beetle
pheromones. This knowledge will allow us to further determine the ecological
role of this widespread forest insect.
Methods
Fifty-two trees were selected within four plots located in the Ozark-St. Francis
National Forest in Arkansas. The trees were assigned treatments in one of two
generations, or “flights”, of Monochamus beetles. All study trees were gauged
as healthy by examination of crown shape, and crown needle condition. In the
first flight three trees per plot were baited in late May with Monochamol (2-
Undecyloxy-1-Ethanol; Synergy Semiochemicals Corp.), aMonochamus sex-
pheromone, and low-release ethanol while a fourth tree received no treatment
(control). Lures were placed ~7 m. above the ground on the north side of the
tree (Figure 4). Due to low response in the first flight, the treatment
combination in the second flight was changed to two trees in each plot for each
of the following treatments: (1) Monochamol + low-release ethanol [ME], (2)
Monochamol + low-release ethanol + Ipsenol [MEI], (3) Ipsenol, and (4) cis-3-
pinene-2-ol [CIS]. Ipsenol is a pheromone produced by Ips bark beetles and is
a known attractant of Monochamus (Miller 2012). The lures for the second
flight were placed in late July.
After initial lure placement trees were checked every two weeks for signs of
Monochamus oviposition pits and any visible change in tree health. This was
accomplished using two sections of Swedish climbing ladders to ascend ~7 m.
up the tree bole and check for pits. All pits were marked with map pins when
they were found (Figure 5).
Results and Discussion
During the first flight our maximum number of pits in a tree was 5
with the average being 1.4 pits per tree. When Ipsenol was added to
trees during the second flight a large increase in oviposition pits
occurred. Numbers of oviposition pits were greatest on Ipsenol treated
trees with a maximum of 65 pits on a tree and an overall mean of 24.5
pits per tree (Figure 6). Oviposition was greatest during the first two
weeks after lure placement with another increase between 6-8 weeks
(Figure 7). This pattern may occur due to lures drying over time
leading to lower release rates. The rise in pits between 6-8 weeks may
occur due to attraction to Ipsenol from increasing numbers of Ips
beetles on treatment trees. Treated trees showed no change in crown
color or foliage loss. Monochamus did not demonstrate a strong
attraction to the ME combination during either flight.
Future Work
Although our results show that Monochamus oviposit into healthy
shortleaf pines, it remains to be determined if any of the eggs hatched
and larval development occurred. Trees with a range of oviposition pit
numbers are being destructively sampled for Monochamus larval
development and adult emergence. If larval development has occurred
it indicates that colonization of healthy shortleaf pines by Monochamus
beetles is possible. Final tree health change will be determined using
crown appearance, resin flow change, and change in needle length.
Monochamus adults are attracted to a
combination of host-produced volatiles
as well as conspecific and bark beetle
pheromones (Miller et al. 2012, Macias-
Samano et al. 2012). Male and female
beetles are attracted to pine trees where
mating occurs. Females then chew
oviposition pits (Figure 2) in the bark into
which eggs are placed. Larvae feed on
phloem creating wide galleries and
eventually enter the xylem to pupate.
Adults eclose and tunnel out of the tree
leaving visible emergence holes in the
bark. Adult Monochamus must feed on
pine twigs before becoming sexually
mature (Figure 3).
References
Albers, M. (2003). Sawyer’s take over 3,000 acres of BWCA [online]. Forest Insect and Disease Newsletter. Minnesota Department of Natural Resources. St. Paul,
MN. Available from http://www.dnt.state.mn.us/fid/nov03/bwca.html
Dodds, K. J., Graber, C., & Stephen, F. M. (2001). Facultative intraguild predation by larval Cerambycidae (Coleoptera) on bark beetle larvae (Coleoptera:
Scolytidae). Environmental Entomology, 30(1), 17-22.
Gandhi, K. J., Gilmore, D. W., Katovich, S. A., Mattson, W. J., Spence, J. R., & Seybold, S. J. (2007). Physical effects of weather events on the abundance and
diversity of insects in North American forests. Environmental Reviews, 15(NA), 113-152.
Linit, M. J. (1988). Nemtaode-vector relationships in the pine wilt disease system. Journal of Nematology, 20(2), 227.
Macias-Samano, J. E., Wakarchuk, D., Millar, J. G., & Hanks, L. M. (2012). 2-Undecyloxy-1-ethanol in combination with other semiochemicals attracts three
Monochamus species (Coleoptera: Cerambycidae) in British Columbia, Canada. The Canadian Entomologist, 144(06), 764-768.
Miller, D. R., Dodds, K. J., Eglitis, A., Fettig, C. J., Hofstetter, R. W., Langor, D. W., ... & Raffa, K. F. (2012). Trap lure blend of pine volatiles and bark beetle
pheromones for Monochamus spp.(Coleoptera: Cerambycidae) in pine forests of Canada and the United States. Journal of economic entomology, 106(4), 1684-1692.
Stephen, F. M. (2011). Southern Pine Beetle Competitors.
Eggs hatch
and larvae
mine the
phloem
and xylem
U-shaped
galleries
created in
which
pupation
occurs
Adults
emerge
from tree
leaving a
large hole
Adults
feed on
pine twigs
to mature
Adults
mate and
female
lays eggs
in pits
Figure 1. An adult male Monochamus
titillator
Figure 2. A Monochamus pit exuding pine
resin
Figure 4. (left) Lures being placed at ~7 m. on healthy
shortleaf pine trees
Figure 5. (right) A Monochamus pit marked with a map
pin near a lure
Figure 7. Average of pits for each two week period after lure placement
Most studies have found that Monochamus are secondary pest insects only
ovipositing in dead or dying trees, however several reports within the last
decade have listed the beetles as the primary cause of death in jack pine
(Albers 2003, Gandhi et al. 2007). Observations of Monochamus attacking
southern pines simultaneously with southern pine beetle suggest that at
high densities they may be partners with aggressive bark beetles in
colonizing host trees (Stephen 2011).
Kevin Collins
Figure 3. Monochamus life cycle
Figure 6. Average number of pits for each lure
0
5
10
15
20
25
30
Ipsenol MEI ME CIS-OL Control
# of pits
Lure Type
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
2 Weeks 4 Weeks 6 Weeks 8 Weeks
Mean pits per tree
Weeks after lure placement
Acknowledgements
We would like to thank the United States
Forest Service for allowing us to conduct
this work within the Ozark-St. Francis
National Forest. The University of
Arkansas Forest Entomology Lab was
essential in providing funding, personnel,
and equipment for the project. The
expertise of Fred Stephen has been
indispensable to our success. We also
thank Dave Wakarchuk and Synergy
Semiochemicals Corp. for the lure
components.
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Sawyer's take over 3,000 acres of BWCA
  • M Albers
• Albers, M. (2003). Sawyer's take over 3,000 acres of BWCA [online].