Thoss, V., and Byers, J.A. 2006. Monoterpene chemodiversity of ponderosa pine in relation to herbivory and bark beetle colonization. Chemoecology 16:51-58.
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Abstract--
Ponderosa pine, Pinus ponderosa Laws.
(Pinaceae), forests in Arizona have suffered from a nine-year
period of drought and bark beetle, Ips lecontei Swaine
(Coleoptera: Scolytidae), outbreaks. Abiotic and biotic stress
in ponderosa pine results in the induced synthesis of certain
monoterpenes that may in turn affect bark beetle behavior
and survival. In this study, we investigate whether induced
monoterpene production could result in a different monoterpene
composition that remains stored in the needles or the
trunk resin of the tree. Needle and resin samples in addition
to trunk cores were collected from ponderosa pines at three
locations in Arizona. Ungulate browsing induced a significant
increase in limonene (P=0.010) and in chemodiversity
(P=0.009), a measure of the evenness of distribution among
the monoterpenes present in needles. We compared the level
of ‘stress’ of the trees by measuring the thickness of annual
rings in living trees and those that were killed by bark beetles.
Where drought occurred, the spacing of annual rings
from the last 10 years of trees killed by bark beetles was significantly
smaller (P=0.020) compared to living trees. There
was no difference in the monoterpene composition between
the core sections of closest spacing of annual rings (stressed
years) compared to the sections of widest spacing, which
indicates that monoterpenes are distributed evenly throughout
the extended resin system. In the area where the degree
of drought was less overall, none of the individual monoterpenes
present in the resin was related to bark beetle killed
trees. However, about half the living pines had resin in
which one of the major monoterpenes (alpha-pinene, 3-carene,
and limonene) was absent, and these trees had a lower
monoterpene chemodiversity compared to trees killed by
bark beetles. Trees with these three major monoterpenes,
corresponding to the average relative proportion in living
pines at that location, may sustain higher selection and
colonization by bark beetles.
Chemical Ecology