1Laboratoire de Zoogéographie, Université Paul-Valéry (Montpellier III), Route de Mende, 34199 Montpellier Cedex 5, France.
2INRA, Station de Zoologie Forestière, Avenue de la Pomme de Pin, Ardon, BP 20619, 45166 Olivet Cedex, France.
The entomofauna associated with seed cones of Swiss stone pine (Pinus cembra L.) includes only three phytophagous species, the species diversity being much lower than that observed in cones of other conifers. The absence of a pine cone weevil, Pissodes validirostris Gyll., that attacks seed cones of most pine species in Eurasia is especially noticeable. Similar observations on related pine species of the P. cembrae subsection lead to the hypothesis that volatiles or oleoresin of stone pine cones may represent a barrier for insect attack. Cone volatiles emitted by P. cembra and other conifers (either ecologically or taxonomically close to P. cembra) were collected using a headspace sampling device, and analyzed using GC and GC-MS. The behavioral responses of adult cone weevils to cone volatiles of P. cembra and Pinus uncinata, an usual host sympatric to P. cembra, were compared using an olfactometer design. The adult weevils were significantly more attracted by the cone emissions from P. uncinata. Cone volatiles of P. cembra elicited an inverse response, most weevils moving in a direction opposed to the odor source. Field sprays of P. uncinata cones with oleoresin extracts of P. cembra cones significantly reduced the overall insect damage, and prevented any damage by P. validirostris. On the other hand, early-instar larvae of P. validirostris extracted from seed cones of P. uncinata and transferred into those of P. cembra were capable of developing to the adult stage. The potential role of cone volatiles in the limited colonization of P. cembra seed cones by insects is discussed.