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The importance of a compound as a repellent is somewhat novel in bark beetle host selection research. Limonene
and other terpenes that kill bark beetles and their vectored fungi have been thought to have a mainly short-range effect as
feeding deterrents (Smith, R.H. 1975, Coyne and Lott 1976). The majority of work in this field, however, has looked for
compounds that increase with stress and are attractive. Few studies have looked for compounds that decrease with stress and
are repellent.
SUMMARY
The significance of these results rests in three principal areas"
1) The large difference in methyl chavicol between healthy and diseased trees provides a clear olfactory sign of stress
for bark beetles, far clearer than has been demonstrated for any monoterpene to date.
2) The stresses that produce the large drop in methyl chavicol are the same stresses that are associated with bark
beetle infestation, suggesting that methyl chavicol is one of the biochemical links between ecology and beetle
behavior.
3) Methyl chavicol reduces the arrestment and landing of bark beetles in the field sufficiently strongly to suggest
management applications for several of our most important bark beetle species with a naturally occurring, abundant
host compound.
Methyl chavicol is the best candidate so far for a compound that responds to stress and to which beetles respond. It
may serve as an indicator and reveal, via biochemical linkage, the elements of host defenses that most strongly affect bark
beetle success. Further investigation of other host species applying stress of the sort known to favor beetle colonization may
determine some new insights for our understanding of the biochemical basis of conifer defenses. Ultimately, we may
understand how environmental stresses that favor beetle colonization produce the characteristics of susceptibility which
beetles favor. We may be able to provide the biochemical linkage between ecological conditions and host selection.
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