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Where beetle response to methyl chavicol was compared by sex, mountain pine beetle males and females were both
significantly less attracted to lures with methyl chavicol. The data for western pine beetle were not sufficient to statistically
test gender-specific response, but methyl chavicol reduced the catch of males by 53% and females by 66%. Methyl chavicol
reduced the catch of D. valens females by 21% and of males by 11%, but neither of these reductions was significant.
DISCUSSION
The aggregation of the two most aggressive bark beetles in this study, the mountain and western pine beetles, was
strongly interrupted. The less aggressive species, D. valens, L pini, and I. paraconfusus were not so strongly affected.
Subsequent testing of the L paraconfusus with methyl chavicol and a larger sample size produced a consistent 40%
interruption of aggregation (Storer, pers. comm.). The aggregation of two other aggressive bark beetles in Alaska, D.
rufipennis and D. simplex, were interrupted by 82% and 73%, respectively (Werner 1995). Haack and Lawrence have tested
methyl chavicol in traps with attractants of Tomicus piniperda (Haack, pers. comm.). Subsequent to the presentation of this
paper, Hayes and co-workers published similar results with Dendroctonusfrontalis (Hayes et al. 1994 a, b) showing 37% and
56% reduction in catch with methyl chavicol (4-allylanisole). Hayes and Strom (1994) also confirmed our results with
mountain pine beetle, obtaining a 77% reduction in catch with methyl chavicol. Their work differed from this work in that
they could not obtain significant interruption of attraction for western pine beetle, and they did find interruption of attraction
at the 43% level for a Wisconsin population of I. pini.
Methyl Chavicol
Methyl chavicol, an aromatic ether or phenylpropanoid, is also commonly known as 4-allylanisole, tarragon, or
estragol. (Other chemical synonyms include: isoanethole, p-allylmethoxybenzene, 4-allyl-l-methoxybenzene, chavicol
methyl ether, esdragon and 1-methoxy-4-2(2-propenyl)benzene) (Aldrich Chemical - Material Data Safety Sheet). It is
widespread in the oleoresin of new world pines in the subgenus Pinus, occurring in P ponderosa, P. taeda, P palustris, P.
elliottii, P patula, P jeffreyi, P. tenufolia, P. hartwegii, P michoacana P. lumholtzii (Mirov1961 and references therein), and
P. caribaea (Smith, R.M. 1975). Among old world pines it occurs in P. sylvestris and P nigra (Bardysev et al. 1970). It is
abundant in the foliage of ponderosa pine (23%) and present in the foliage of lodgepole and digger pines (Mirov 1961). It is
also found in 12 or more species of spruce (Zavarin, pers. comm.).
Methyl chavicol is the principal volatile ingredient or a major volatile of several strongly scented herbs: tarragon,
Artemisia dracunculus; fennel, Foeniculum vulgare; star anise, Illicium verum; basil, Ocium basilicum; and cloves, Szygium
aromaticum (Duke 1985). Methyl chavicol is also known from the leaves of three rutaceous plants, west african zigua,
Clausena anisata, where it is the major component of the oil of leaves used to repel mosquitoes (Okunade and Olaifa 1987);
7_nthoxylum spp., where it is toxic to Dacus eggs (Marr and Tang 1992); and southeast asian wood apple, Feronia limonia
(Ahmad et al. 1989). In addition, it is found in oil palm, Elaeis guineensis, where it is attractive to the weevil Elaeidobius
kamerunicus (Hussein et al. 1990). In recent plant herbivore studies, it is most well known from the work of Metcalf and his
co-workers. They have found it in the flowers of Cucurbita maxima, where it is attractive to Diabrotica spp., corn rootworms.
This association is the basis of a productive research effort in biorational management of Diabrotica (Metcalf and
Lampman 1989).
Biosynthetically methyl chavicol is derived from the shikimic acid pathway (Zavarin et al. 1971). This pathway is
disrupted by the herbicide glyphosate (Roundup, Monsanto) (Borden, pers. comm.). Interestingly, when Bergvinson and
Borden (1991) applied glyphosphate to lodgepole pine, they found that treated trees were readily colonized by mountain pine
beetles. They concluded that the herbicide had inhibited the treated trees' secondary defense response against the beetle's
symbiotic fungi. This is consistent with the hypothesis that the success of mountain pine beetles in glyphosate-treated trees
is, in part, due to a drop in methyl chavicol. Bridges (1987) found methyl chavicol was the most inhibitory host compound to
the three symbiotic fungi associated with D. frontalis, suggesting that it may be an important defensive mechanism of loblolly
pine against southern pine beetle and its vectored fungi. Hayes et al. (1994a) found that methyl chavicol was strongly
reduced in southern pines following wounding and treatment with metham-sodium and dimethyl sulfoxide. Treated trees
were attacked by D. frontalis after the level of natural methyl chavicol dropped. Methyl chavicol tested subsequently in field
bioassays strongly reduced attraction of southern pine beetle to pheromone-baited traps.
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