WWETAC Projects

Project Title: Continuing investigation of the introduced parasites of larch casebearer (Coleophora laricella) in the Blue Mts. Oregon and throughout the Pacific Northwest with additional consideration of alpine larch

Principal Investigators: David Shaw, Department of Forest Engineering, Resources and Management, Forestry and Natural Resources Extension, Corvallis, Oregon; Paul Oester, Department of Forest Ecosystems and Society, Forestry and Natural Resources Extension, La Grande, Oregon


: Roger Ryan, retired, USFS Pacific Northwest Research Station, Corvallis, Oregon

Key Issues/Problems Addressed:

This is a continuation of a project that had focused on the Blue Mountains region in field season 2010 (“Are the introduced parasites of larch casebearer (Coleophora laricella), still present in the Blue Mountains, Oregon?”), but now we have expanded the project to include all western larch habitat in Oregon, Washington, Idaho and Montana, as well as some alpine larch sites in Washington State.  Weather and logistics made visiting alpine larch sites in Montana difficult.

Setting and Approach:

In order to examine the population dynamics of larch casebearer parasitoids in the Blue Mountains of Oregon we plan to revisit the 13 study sites there and do a winter (March/April) sample.  (Ideally we would sample over 3-4 years to get a good idea of populations trends.) We will sample at increasing distances from release sites in the Blue Mountains, the Ochocos and the eastern Cascades to analyze the distribution of larch casebearer parasitoids in relation to their release sites. A summer (May/June) sampling program across the distribution of western larch will sample for parasite presence and abundance to determine if are larch casebearer parasitoids present within the entire range of western larch and if there is any geographic variation in distribution (ie, Does the parasite distribution follow any temperature gradients?) During the summer sampling period, we will also visit alpine larch sites and sample them to determine if larch casebearer and parasitoids are present.

Progress to Date:
In 2011 we sampled the 13 Blue Mountain study sites in winter, and followed up with winter/very early spring sampling of sites on the Ochoco, Mt. Hood, and Deschutes NF in Oregon. We succeeded in processing winter samples and estimating % parasitism and gaining more understanding of Chrysocharis laricinellae using these winter samples.  We are still in the data analysis mode, and will include the analyzed data in the final report.

Our sampling of additional areas in relation to release sites indicates Agathis  pumila and Chrysocharis laricinellae are spread throughout the region of western larch, with no particular pattern in relation to documented release sites.

We sampled 15 sites in Washington, 15 sites in Montana and 10 sites in Idaho for a total of 352 trees.  First cut data analysis indicates that A. pumila was present at 74% of the sites (average of 11.1 individuals/tree) and Chrysocharis laricinellae was present at 63% of the sites (average of 2.6 individuals/tree).  These are significant numbers indicating persistence of these two parasitoids 30-40 years after release.  Larch casebearer densities ranged from 0.1 moths/100 larch buds to 80 moths/100 larch buds while total % parasitism ranged from 0 to 93%.  It appears that C. laricinellae is more common in WA, MT, and ID than it was in the Blue Mts.  Other native parasitoid wasps are more abundant at some locations also. Finally, we have documented 15 other native parasitoid wasps from larch casebearer and one unknown species.

We visited four alpine larch sites in the North Cascades, WA in Fall of 2011 and ran transects to sample for occurrence of larch casebearer.  We found no indication that larch casebearer was present, and it appeared that these larch stands are very healthy, with general herbivory (from any herbivore) under 5%.  We were not able to get into alpine larch sites in Montana during the 2011 field season.

WWETAC Project ID: FY10TS74a

larch casebearer damage