Chemical Ecology of Sudden Oak Death/
Ambrosia Beetle Interactions1
Frances S. Ockels2, Pierluigi Bonello2,3, Brice McPherson3 , and
David L. Wood3
Key words: ambrosia beetles, coast live oak, Phytophthora ramorum, volatile
Abstract
Coast live oaks, Quercus agrifolia, infected with Phytophthora ramorum in California
produce a characteristic sequence of symptoms and signs. Ambrosia beetles consistently
tunnel into the bark of bleeding cankers in naturally infected trees. In field monitoring
conducted since 2000, every bleeding coast live oak that subsequently died had been
colonized by beetles while bleeding cankers were the only symptom of P. ramorum infection.
Although the function of these beetles in decline and death of infected trees has not been
confirmed, they likely disrupt nutrient and water conduction and accelerate structural failure
(McPherson and others 2005). In mechanically inoculated trees, beetles colonize the cankered
areas within nine months of inoculation. This behavior is not consistent with the reported
feeding ecology of the saprotrophic insects (Chamberlain, 1958; Furniss and Carolin, 1977;
Wood, 1982; McPherson and others 2005). In an inoculation study, we used traps to monitor
the response of beetles to both infected and wounded but uninfected trees. Traps placed on
inoculated trees caught significantly more scolytid beetles than traps on trees that were only
wounded. Six species of saprotrophic beetles are now known to be attracted to these infected
trees. This directed response to native oaks infected by a putative introduced pathogen points
to the production of volatile chemical attractants (kairomones). Volatile samples were
collected in two ways. Firstly, samples of volatiles emitted from the bark of infected and
control oaks were collected in the field by strapping the mouths of 1-L plastic bottles directly
onto the bleeding produced by cankers on inoculated trees, and over the site of the
“inoculation holes” on the uninfected, but wounded trees. The point where each bottle rested
against the bark was sealed to minimize mixing with external air. Alternatively, the “blood,”
the dark colored exudate released by cankers, was placed in a vial and sealed. In both cases,
samples were collected 24 h later by exposing solid phase micro-extraction (SPME) fibers to
the atmosphere inside the bottles/vials for 30 min. The samples were analyzed by gas
1
A version of this paper was presented at the Sudden Oak Death Second Science Symposium: The
State of Our Knowledge, January 18-21, 2005, Monterey, California
2
Environmental Science Graduate Program, The Ohio State University; ockels.1@osu.edu
3
Department of Environmental Science, Policy, and Management, University of California, Berkeley
423
GENERAL TECHNICAL REPORT PSW-GTR-196
chromatography-mass spectrometry (GC-MS) using the method of Martin and others (2003).
Identification of eluting compounds was based on matching with natural product spectra
contained in the Wiley Registry of Mass Spectral Data and the NIST Library. Preliminary
results from GC-MS analysis identified, with a high confidence level, 4-ethylphenol, 4ethlyguaiacol, and 4-propylguaiacol among the peaks. These compounds are volatile
phenolics. Phenolics are known to be involved in host defense responses to microbial
pathogens. Coast live oaks may respond to P. ramorum infection and canker development by
producing volatile phenolics that in turn are attractive to ambrosia beetles. Future work to test
this hypothesis includes: collecting additional volatiles for GC-MS analysis, initiating
quantitative studies, and conducting field experiments to test behavioral effects of the
identified compounds.
RT: 0.00 - 42.70
31.55
100
4-Propylguaiacol
NL:
1.42E6
TIC MS
SR13Blood
95
90
85
80
4-Ethlyguaiacol
75
70
Relative Abundance
65
60
55
4-Ethylphenol
50
27.70
45
17.05
40
35
30
25
22.77
15.39
7.00
20
19.20
14.42
15
2.28 2.73 4.16
26.37
12.70
8.45
10
11.13 12.58
6.74
36.81
36.34
29.65
21.84
19.46
24.44
20
22
Time (min)
24
42.19
33.71
35.84
37.39
40.64
5
0
0
2
4
6
8
10
12
14
16
18
26
28
30
32
34
36
38
40
Figure 1— Gas chromatogram of the “blood” displaying subset of compounds identified by
GC-MS analysis.
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42
Proceedings of the sudden oak death second science symposium: the state of our knowledge
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(Coleoptera:Scolytidae), a Taxonomic Monograph. Brigham Young Univ., Provo.
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