PARENT SESSION
Poster Session 37: Forest Ecology.

Thursday, August 5 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Swiss needle cast effects on Douglas-fir stem ethanol, oleoresin, and Douglas-fir beetle host selection.

Kelsey, Rick^*,, Manter, Daniel,

ABSTRACT- Douglas-fir, Pseudotsuga menziesii, growing on the western slopes of the Oregon Coast Range are experiencing an unprecedented outbreak of Swiss needle cast (SNC) by the fungus Phaeocryptopus gaeumannii that is causing substantial physiological stress and slower growth. Stressed Douglas-fir are often susceptible to attack by the Douglas-fir beetle, Dendroctonus pseudotsugae, but there are no current reports of increased beetle activity or outbreaks associated with these diseased forests. We examined the influence of SNC on Douglas-fir beetle activity and some tree physiological parameters that may affect beetle attraction (i.e., constitutive ethanol and alpha-pinene contents of woody tissues) and host susceptibility (i.e., wound-induced resin flow). Woody tissue ethanol concentrations, wound-induced resin flow, and beetle attraction were all reduced as SNC severity increased. If ethanol functions as a signal of physiological stress, then Douglas-fir beetles may have difficulty recognizing SNC stressed trees because of their low ethanol concentrations. Although trees affected by SNC attracted fewer beetles, the number of attacks did not decline, attacks were more likely to penetrate to sapwood depth, and galleries were longer than in healthier trees, most likely due to a weakened oleoresin defense. Furthermore, beetle populations may not be increasing since stressed trees appear unsuitable for reproduction, as no eggs, larvae, or adult beetles were observed in excavated galleries on any attacked trees. However, if suitable host materials became available from some catastrophic event (e.g. wildfire or wind-throw), and the beetles can reproduce successfully then the potential for a devastating outbreak of Douglas-fir beetle in SNC stressed trees might be exacerbated because they have compromised oleoresin defense systems.

Key words: bark beetles, ethanol, douglas-fir, stress