Volatile Compound Chemistry and Insect Herbivory: Pinus edulis Engelm. (Pinaceae) Seed Cone Resin

Pinus edulis Engelm. (pinyon pine) is a tree in the Pinaceae family with wide geographic distribution throughout dry forests of western North America. Pinyon pine seed cones, which mature over a 2-year period before shedding seed, are often resinous. Conifer resin, which is a liquid-soluble mixture of volatile and non-volatile secondary metabolites, typically demonstrates significant ecological functions. In the current study, seed cones (n = 240) were collected monthly for a 1-year period from pinyon pine trees (n = 20) and separated equally into two groups, resinous and non-resinous cones, for research on the volatile compound chemistry and insect herbivory. Upon distillation, resinous cones yielded 41× more volatile oil and contained more viable seeds, compared to non-resinous cones. Chemical profiles of volatile oils were seemingly consistent between seasons but differed between cone groups. In resinous cone samples, volatile oils were largely composed of α-pinene (avg. 75.6%) and δ-3-carene (avg. 7.4%). In contrast, in non-resinous cone samples, the volatile oil profiles were not dominated by any single prominent compound. Cone inquiline insect communities varied with regard to the resinous status of the cones, the month of collection, and with overall volatile oil yield. Typically, with larger oil yields we saw more diverse and more abundant inquiline communities. Findings from this study suggest that the volatile oils, in addition to other components of cone resin and physical structures, play a significant ecological role in pinyon pine seed preservation from insect herbivory.