Comparison of the defense reactions of Pinus pinaster and Pinus sylvestris to attacks by two bark beetles (Coleoptera: Scolytidae) and their associated fungi.
Lieutier F. | Cheniclet C. | Garcia J.
Experimental introductions of the two bark beetles Tomicus piniperda L. and Ips sexdentatus Boerner and inoculations with patches of agar cultures of their associated fungi (respectively Leptographium wingfieldii Morelet and Ophiostoma brunneo-ciliatum Math.-K. (Hunt) were performed and compared in a clone of Pinus pinaster Aitone and some forest trees of Pinus sylvestris L. Results were similar in the two pine species. Tree response to fungal inoculation was characterized by a considerable increase in the concentration of all the phloem monoterpenes. No qualitative differences in the major monoterpenes were noticed between induced resin and performed resin. For an introduction of T. pinipderda, terpene concentration was always lower than for an inoculation of L. wingfieldii. After an introduction of I. sexdentatus, terpene concentration was lower than or equal to that obtained after an inoculation of O. brunneo-ciliatum. The inoculation of diversified quantities of spores in sterilized water to Scotch pine demonstrated a dose-dependent tree response (expressed as resin concentration in the phloem) to the two species of fungi. The intensity of the response increased to a similar level for the two fungus species. In the case of O. brunneo-ciliatum, this level was reached for a quantity of spores much lower than in the case of L. wingfieldii. Consequently, the difference in the intensity of the tree response to T. piniperda and L. wingfieldii might be explained by the lack of fungus associated with the attacking insects or by too low a number of spores introduced by the insects in their galleries. In the case of I. sexdentatus and O. brunneo-ciliatum, the variable response of the tree from one insect to another might depend only on the presence or the absence of a fungus in the insect gallery.
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