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STEVEN J.
SEYBOLD
Assistant Professor
Forest Entomology
Departments of Entomology and Forest Resources
UNIVERSITY OF MINNESOTA
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UPDATE
on Recent Lab Activities |
| RESEARCH
INTERESTS
BACKGROUND: My research focuses on the biochemistry,
molecular biology, and chemical ecology of wood-destroying insects.
The biodeterioration of woody tissue is a natural process that has
both ecological and economic implications, and insects play key
roles in all stages of the degradation of wood. The insects that
have the most obvious impact on the growth, health, and longevity
of wood are the conifer-infesting bark beetles that colonize living
and moribund trees and feed in the phloem/xylem interface. These
beetles (Coleoptera: Scolytidae) mass attack trees, and their aggregations
are guided by aggregation pheromones composed of volatile oxygenated
terpenoids, isoprenoids, oxygenated alkanes, and bicyclic acetals.
I am studying the biogenesis of these bark beetle aggregation pheromones,
including the endocrine regulation, the de novo biosynthetic
pathways, and the anatomical localization of the key enzymes. My
research is currently centered on four economically important pine-infesting
bark beetle species: the California five spined ips, Ips paraconfusus,
the pine engraver, Ips pini, the Jeffrey pine beetle, Dendroctonus
jeffreyi, and the mountain pine beetle, Dendroctonus ponderosae.
The Ipsspp. synthesize most of their acyclic monoterpene
alcohol pheromone components de novo, with only small amounts
derived from the hydroxylation of the host monoterpene myrcene.
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| The
adult male pine engraver, Ips pini |
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| The
Jeffrey pine beetle, Dendroctonus jeffreyi |
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| SOME KNOWN
BARK BEETLE SEMIOCHEMICALS |
| ISOPRENOIDS
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OXYGENATED
ALKANES |
BICYCLIC
KETALS |
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| Ipsdienol
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Ipsenol |
Amitinol |
E-myrcenol |
1-Heptanol |
exo-Brevicomin |
Frontalin |
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| Ipsdienol and Ipsenol
— Common aggregation pheromones observed in Ips spp. |
| Place mouse
over structures to view different molecular orientation |
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R-Ipsdienol |
S-Ipsdienol |
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R-Ipsenol
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S-Ipsenol
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BIOORGANIC, BIOCHEMICAL,
AND MOLECULAR APPROACHES:
Techniques currently utilized for our
in vivo and in vitro studies of bark beetle biochemistry
include bioorganic separation and analysis of pheromone components
by HPLC, GC, and GC-MS (view some
of our lab equipment); radiotracer studies with radiolabeled
acetate and radiolabeled mevalonate precursors; and molecular
analysis of messenger RNA for HMG-CoA reductase (HMG-R) using
RACE PCR and gel electrophoresis. Biochemical studies have suggested
that the latter enzyme is crucial for the induction of isoprenoid
pheromone production. Specificially, with male Ips pini,
the biosynthesis and release of the the insect sesquiterpenoid
developmental hormone juvenile hormone (JH) is stimulated from
the corpora allata during feeding. JH then mediates an increase
in HMG-R transcript levels and/or enzyme activity to result in
increased carbon flow through the isoprenoid pheromone biosynthetic
pathway. One of the central issues of these studies is the stereoselectivity
of the biosynthesis, and enantiomeric biosynthetic products are
frequently further analyzed by GC with chiral stationary phases.
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Click
here to view expanded biosynthetic
pathway
that includes regulatory aspects |
| SOME REPRESENTATIVE
RESEARCH FINDINGS: |
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The production of
n-heptanol and 2-heptanol in female Dendroctonus jeffreyi and
the production of frontalin and exo-brevicomin in males is
stimulated by exposure to n-heptane, as shown by gas chromatography
of hindgut extracts following exposure to n-heptane for 24
hours. n-Heptane is a hydrocarbon present in host (Pinus
jeffreyi) resin. |
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In vitro
HMG-R activity in
male Ips pini is stimulated
by both JH III and feeding
on host phloem. It is known
that both treatments result in increased levels of HMG-R transcript
as well. Measurement of HMG-R protein levels in treated insects
will determine if JH III mediates an increase in protein levels
(via increased transcription or translation rates and/or increased
protein stability) and/or activity of exisiting protein to result
in an increase in observed activity. |
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HMG-CoA reductase
(HMG-R) transcript levels in male JH III-treated male Ips pini
are higher in a dose-dependent manner in male Ips pini,
as shown by northern blot. This indicates that JH produced by the
corpora allata upon feeding contributes to the stimulation of pheromone
production by mediating an increase in a key enzyme in the isoprenoid
biosynthetic pathway, HMG-R. |
| APPLIED CHEMICAL ECOLOGY: |
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| A pheromone-baited funnel trap for
bark beetles. The dark cylindrical silhouette of the trap
mimics the dark silhouette of the trees in the background
(S.J. Seybold, Photo) |
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| We are also interested in
the behavioral activity of bark beetle aggregation pheromones,
and a major project in the lab is determining the optimal attractant
for D. jeffreyi, a noticeable pest of Jeffrey pine in
California and Oregon. This work involves laboratory and field
behavioral assays to assess the effect of enantiomeric composition
and relative mass composition of the chemical components of
the attractant on the walking and flight behaviors of the beetles.
The determination of interruptant semiochemicals (behavioral
inhibitors) for D. jeffreyi is also being pursued. Another
area of interest in bark beetle biochemistry is the characterization
of cuticular hydrocarbons of bark beetles. |
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| A stand of Jeffrey pine,
Pinus jeffreyi, attacked by the Jeffrey pine beetle,
Dendroctonus jeffreyi, in the Tahoe Basin (J.M. Riba,
Photo) |
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| The long term goal of this research is to
develop biorational techniques to manage insects based on non-toxic
behavioral chemicals. A thorough understanding of the biosynthesis
and activity of insect behavioral chemicals will aid in their ultimate
application to insect management. Future research projects on the
biosynthesis and activity of behavioral chemicals are planned for
later stage wood-destroying insects of local importance such as carpenter
ants (Hymenoptera: Formicidae) and deathwatch and powderpost beetles
(Coleoptera: Anobiidae and Lyctidae). |
| MULTISTATE
RESEARCH PROJECTS:
I collaborate with other scientists interested
in forest entomology, insect chemical ecology, and insect biochemistry
through my memberships in two Multistate Research Projects:
W187:
Interactions Among Bark Beetles, Pathogens, and Conifers in North
American Forests
W189:
Biorational Methods for Insect Pest Management: Bioorganic and Molecular
Approaches |
| My research program on the biochemistry
and molecular biology of bark beetle aggregation pheromone production
has been supported by the Human Frontier Science Program, the USDA
National Research Initiative Competitive Grants Program (#9302089,
#9502551, #9702991, #9802897), by the National Science Foundation
Integrative Animal Biology Program (#IBN-9906530), and by the USDA
Forest Service, particularly the Chemical Ecology of Forest Insects
Project, Research Work Unit #4502, Pacific Southwest Research Station,
Albany, California. Other projects in my laboratory are supported
by the California Structural Pest Control Board, the Legislative Commission
on Minnesota Resources, and the USDA Forest Service Forest Health
Protection Special Technology Development Program. |
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to main Seybold Forest Entomology page |
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This page last updated on Thursday, January 16, 2003
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