WWETAC Projects

Project Title: Are the introduced parasites of larch casebearer (Coleophora laricella), still present in the Blue Mountains, Oregon?

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

dave.shaw[at]oregonstate.edu

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

Key Issues/Problems Addressed:

Western larch (Larex occidentalis Nutt.) experience significant defoliation from the larch casebearer (Coleophora laricella (Hubner)). Known parasites of larch casebearer, predominantly Agathis pumila (Hymenoptera: Braconidae) and Chrysocharis laricinellae (Hymenopter: Culophidae), were successfully introduced in a biological control program in the 1960s within the Blue Mountains of Oregon and Washington. Researchers observed larch casebearer defoliation in the region in 2007 and 2008, yet it is unknown whether the parasitoid wasps are still present and how they may presently impact the larch casebearer.

Setting and Approach:

A total of 29 sites located in the Blue Mountains of northeast Oregon and southeast Washington were studied.
In June 2010, researchers sampled 13 “core” historical release sites or check sites for larch casebearer population status (number moths per 100 western larch buds), parasitoid wasp species occurrence, and percent parasitism of the larch casebearer caused by parasitoid wasps. Sixteen new locations were sampled at varying distances from the core sites to determine if A. pumila occurs across the landscape.

Key Findings:

  • Agathis pumila was found at every site, while C. laricinellae was found in high densities at the core sites, but in relatively low densities at the 16 new sites.
  • Twelve native species of larch casebearer parasitoid wasps were found, although not as commonly as A. pumila or C. laricinellae
  • Larch casebearer had a mean density of 7.26 moths per 100 buds at all core sites (compared to the 10 year average of 1.63 moths per 100 buds, last sampled in 1995) and was present at all 29 sites.
  • Parasitism percentages ranged from 1.82 to 53.4 percent. 
  • Moth densities were lower where parasitism rates were high as moth density was negatively correlated with percent parasitism by A. pumila (p<.0001).

Impacts/Applications:

Agathis pumila may continue to be an effective control agent of larch casebearer since it was the most abundant and widespread parasitoid wasp found during this study.

WWETAC Project ID:  FY10TS74

larch casebearer damage