Thuja occidentalis: identification of volatiles and electroantennographic response by the invasive cedar bark beetle, Phloeosinus aubei
2016
Recently, the distribution of the Mediterranean cedar bark beetle,
Phloeosi-
nus aubei
Perris (Coleoptera: Scolytidae), has expanded to Central Europe.
Reported mostly on cypress in the Mediterranean area, potential host
plants in the invaded range include other scale-leafed conifers, such as cul-
tivars of arborvitae,
Thuja occidentalis
L. To reveal potential kairomonal cues
for
P. aubei
, volatiles of
T. occidentalis
were collected and analysed by gas
chromatography with electroantennographic detection (GC-EAD). Assign-
ments of chemical structures of antennally active components were carried
out by gas chromatography linked to mass spectrometry (GC-MS) using
authentic reference samples. Antennal responses to synthetic samples of
the identified compounds were studied by electroantennography (EAG),
with antennae of female and male
P. aubei
. GC-EAD analysis of head space
volatiles of
T. occidentalis
revealed 22 antennally active compounds, of
which 21 were identified. The most abundant components were
a
-and
b
-
thujone, fenchone, camphor, terpinen-4-ol, bornyl acetate and
a
-terpinyl
acetate, all of which are oxygenated monoterpenes. When EAG activities
of synthetic samples were compared, the most intensive responses from
female antennae were elicited by a mixture of
a
-and
b
-thujone, followed
by (
–
)-terpinen-4-ol, (
+
)-camphor,
cis
-4-thujanol, (
+
)-sabina ketone, (
+
)-
terpinen-4-ol, isopulegone, (
–
)-fenchone, borneol, (3
Z
)-hexen-1-ol, (
–
)-1-
octen-3-ol and (
+
)-sulcatol. Male antennae responded the most to (
–
)-ter-
pinen-4-ol and
cis
-4-thujanol followed by the mixture of
a
-and
b
-thujone.
The next highest responses were elicited by (
+
)-camphor, borneol, (
+
)-ter-
pinen-4-ol, (
+
)-sulcatol and (
+
)-sabina ketone. Striking differences were
found between responses to the enantiomers of fenchone, sulcatol and 1-
octen-3-ol, whereas responses to the enantiomers of terpinen-4-ol did not
differ significantly from each other. Several antennally active volatiles of
T. occidentalis
have also been reported from cypress and various other
members of the Cupressaceae, suggesting that the sensory apparatus of
P. aubei
may recognize the shared components, which may enable rapid
adaptation to new hosts in the invaded areas.
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