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Interactions between resin flow and subcortically feeding Coleoptera Under investigation is the dual function which oleoresin apparently has in the colonization of conifers, particularly pine trees, by subcortically feeding insects: Oleoresin represents a factor in host resistance against insect attack as well as an agent in host recognition and pheromone release. On the background of common observations, that certain insects i. e. bark beetles attack preferably lightning hit, cut or otherwise damaged or weakened trees, we analyse the hypothesis that physiological changes may affect the terpene chemistry of pine trees: does a tree's bouquet of semiochemicals differentiate “susceptible” from “resistant” hosts? In an experimental approach to test such hypothesis, injection of the herbicide paraquat readily increased resin emmission and the probability of attack of the treated trees by scolytids and cerambycids; but no significant differences were detectable in the xylem resin of treated trees before or after treatment, and untreated trees, respectively. However, resin samples obtained from the bark surface of treated trees contained traces of additional compounds that represent a variety of oxidation products of host monoterpenes. The informations available so far are interpreted that the more aggressive bark beetles respond primarily to host material that varies little or none from a healthy tree except for a stronger emanation of resinous odors, and possibly, terpenoid oxidation products formed by the exuding resin on the tree's surface. Thus, exposure of resinous material per se may be responsible, in part, for the observed preference of damaged host trees by subcortical feeding insects. Zusammenfassung Fur die Beobachtung und experimentelle Uberprufung der Rolle, die der Harzbalsam in der Besiedlung von Nadelbaumen durch rindenbrutende Insekten (insbesondere Borkenkafer) spielt, eignen sich offenbar Stamminjektionen mit dem Herbizid Paraquat. An stehenden Kiefern fuhrt die Herbizideinwirkung neben Resinosis in einem begrenzten Stammbereich zur Bildung von Harzbeulen (Pinus silvestris) bzw. tropfenweisen Harzaustritt (Pinus elliottii) und nachfolgendem Befall durch Borkenkafer. Wahrend eine Veranderung des Terpenmusters im Xylemharz der behandelten Baume nicht nachweisbar war, enthielten von der Rindenflache gesammelte Harzproben zusatzlich oxidierte Terpene, die moglicherweise neben der Harzausscheidung per se eine Rolle in der Primaranlockung rindenbrutender Kafer spielen mogen. |
