In terms of the risk of damage to Valley
ponderosa pine by insects, localized outbreaks of bark beetles represent the
most significant threat (Fig. 1). However, historically no comprehensive
trapping survey of bark beetles had been completed. Funding provided by the USDA
Forest Service in 2008 and 2009 has allowed us to assess the diversity of bark
beetles that occur over the range of Valley ponderosa, and reported here are the
results of pheromone-baited trapping completed at 11 sites along a North
(Beaverton) to South (Creswell) gradient from May-October 2008 and April-October
2009.
Thus far, over 25,000 bark beetles have
been collected, using a number of general as well as species-specific lures
(Fig. 2). At all sites, the overwhelming majority of bark beetles captured were
the California five-spined Ips (Ips paraconfusus), which in recent years has
been the most frequently observed to cause damage to Valley ponderosa pine.
Several closely related species (Ips
latidens, Ips pini, Pseudips mexicanus)
were also detected in small numbers at several sites. Other potentially damaging
bark beetles, also collected in small numbers, included Dendroctonus species
such as the red turpentine beetle (D. valens), western pine beetle (D.
brevicomis), and even mountain pine beetle (D. ponderosae). Although samples are
still being processed, the remainder of beetles collected appear to be
“secondary” bark beetles, which typically only infest already dead or dying
trees.
All bark beetles examined thus far are native to Oregon, and such a wide diversity is not unexpected. However, the historical distribution of beetles such as the pine engraver (Ips pini), as well as the western and mountain pine beetle, does not typically include the Valley. These beetles are adapted to the warmer, drier climates of eastern and southwest Oregon. The small number detected in the survey suggests that they likely originated from some type of wood product being moved to/through the Valley, as reproducing populations of these beetles have not been previously documented here.
Of all the bark beetles found in the survey, the one of greatest concern continues to be the California five-spined Ips. Analyses of its peak flight periods and how this relates to environmental conditions are ongoing, and we hope to have more detailed information soon. But, regardless of the specific timing, continued vigilance in avoiding large amounts of larger diameter (>3”) pine storm-damage/slash will be needed through the spring and summer, to reduce the potential for build-ups and localized outbreaks.
Due to the high variation between years, we plan to repeat aspects of the study in 2010. And, it is hoped that this will provide a more complete picture to help in refining beetle management guidelines in Valley ponderosa pine. This project has also provided a baseline as to the current diversity and distribution of bark beetles in the Valley, as many climate models indicate that changing conditions may allow a greater number of damaging bark beetles to occur here in the future.
