Host Selection and Wood Channelization by Beetles in Conifer Logs in Western Oregon

The host preferences and wood channelization rates of scolytid and cerambycid beetles were studied at the H. J. Andrews Experimental Forest (Lane County, Oregon) during 1986 and 1987. Attack density and gallery volumes were measured in fall-felled experimental logs of four major
conifer species: Douglas-fir (Pseudotsuga mensiesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.)Sarg.), Pacific silver fir (Abies amabalis (Dougl.)Forbes), and western redcedar (Thu'a plicata Donn).

The ambrosia beetles (Coleoptera: Scolytidae), Trypodendron lineatum (Olivier) and Gnathotrichus spp., were significantly more abundant in Douglas-fir and western hemlock than in silver fir or western redcedar, but
Xyleborinus saxeseni (Ratzeburg) showed no discrimination among the four tree species. The average emergence of ambrosia beetle brood per gallery was 1.8 in spring-felled Douglas-fir logs and 2.2 in western hemlock. The data indicate a declining ambrosia beetle population emerging
from these logs.

About 0.16% of the sapwood volume of Douglas-fir andabout 0.18% of the sapwood volume of western hemlock were removed by Trypodendron. About 0.01% of the sapwood volume of Douglas-fir and about 0.06% of the sapwood volume of western hemlock were removed by Gnathotrichus.

The bark beetles (Coleoptera: Scolytidae) Dendroctonus pseudotsugae Hopkins and Dryocoetes autographus Ratzeburg excavated about 7.6% of Douglas-fir phloem surface area. Pseudohylesinus sericeus (Mannerheim) removed 6.8% of Pacific silver fir phloem surface area. Long-horned beetles
(Coleoptera: Cerambycidae) excavated an additional 2.3% of Pacific silver fir phloem surface area.

These data indicate that each tree species has a distinct boring insect species pool with differences in channelization rates through time. Colonization and fragmentation of fallen trees by beetles are important to
the initiation of the decomposition process in forest ecosystems.