Girdled Trap Trees for Survey and Detection of Emerald Ash Borer

Research Issue

Early detection of new EAB infestations is critical for implementing rapid and focused responses to control and contain the infestation.  Accurate delimitation of the area infested by EAB is critical for regulatory officials who must establish the quarantine boundaries and implement control measures.  Survey crews initially relied on signs and symptoms such as adult exit holes, bark splits over galleries, epicormic shoots, or canopy dieback to identify potentially-infested trees.  Newly infested trees, however, typically demonstrate no external symptoms, making it difficult to truly delineate the EAB infestation.  Methods to attract and trap adult beetles, which are likely to be present for 10 to 12 weeks in the summer, would substantially increase our ability to identify new infestations and the leading edge and extent of the EAB distribution. 

 Our Research

From 2003 to 2007 we conducted several experiments to compare EAB attraction to healthy ash trees or trees that were stressed by girdling, wounding, treatment with herbicide, or treatment with the hormone methyl jasmonate (MeJA) that promotes the production of stress-induced volatiles.  In 2003, we evaluated trap logs and healthy trees, girdled trees, or trees treated with the herbicide, Pathfinder.  In 2004 we compared healthy trees, girdled trees, wounded trees and trees treated with the herbicide Garlon-4.  In 2005, we evaluated the number of adults captured and subsequent larval density on trees that were girdled, treated with Garlon 4 herbicide, exposed to MeJA, or left as untreated controls.   In 2006, we conducted a similar study to compare adult EAB capture rates and larval densities on trees treated with different stress agents: girdle, MeJA, Manuka oil, and control.  Half of the replicates were dissected at the end of 2006 to determine larval density.  The remaining trees were evaluated in 2007.  Trees used as healthy controls in 2006 remained as control trees in 2007, trees girdled in 2006 now represented a 2-year girdle treatment, and trees previously treated with Manuka oil were girdled in the spring of 2007 (1-year girdle).  Trees treated with MeJa in 2006 were wounded by removing a vertical strip of bark of the same area of bark as a standard girdle, leaving most of the phloem around the circumference of the tree intact.

Expected Outcomes

To date, girdled trap trees remain the most effective method for detecting low density populations of EAB.  Regulatory agencies have implemented the use of girdled trap trees in statewide surveys for EAB.  Several new infestations have been detected as a result of girdled trap trees, including a new infestation in Michigan’s Upper Peninsula.

Research Results

In 2003, our results demonstrated that more EAB adults were captured in sticky bands applied to girdled ash trees than in similar bands on healthy trees or cut ash logs.  Trees treated with Pathfinder herbicide were not badly stressed but were somewhat attractive and captured an intermediate number of beetles.  In 2004, we found that significantly more EAB were captured on girdled trees than trees that were wounded or treated with Garlon-4 herbicide.  In 2005, we again found that significantly more EAB adults were captured on girdled ash trees than on healthy control trees or treated with MeJA.  The number of EAB captured on trees treated with Garlon 4 herbicide did not differ significantly from the girdled or MeJA trees.  Significantly more galleries per m2 were found on the girdled trees than on the MeJA, herbicide, or control trees.  Results from this study and related work in 2004 demonstrated herbicide-treated trees are generally dead or dying by mid to late summer and are either unattractive to ovipositing EAB females or unsuitable for larval development. Girdled trees captured significantly more EAB than the control trees at all sites, regardless of EAB density.  In 2006, we again found significantly more EAB captured on girdled trees than on healthy control trees.  The number of EAB captured on the trees treated with MeJA or Manuka oil tended to be slightly higher than the number on the control trees, but differences were not significant.  When considering canopy exposure of trees, more than 90% of the EAB captured were on trees that were fully exposed or had 2-3 sides exposed to sunlight.  In 2007, beetle densities increased three to 10 fold at all field sites.  Seven of 20 trees girdled in 2006 died by early summer in 2007.  High numbers of adult EAB were captured on all trees remaining from 2006.  At very high population densities, all ash trees appear to be attacked and there were no significant differences between treatments.  In summary, over 4 years of trap tree experiments at sites with low to moderate EAB population densities, girdled trees have consistently been found to be the most attractive for EAB.

Storer, Andrew J.; Metzger, Jessica A.; Fraser, Ivich; McCullough, Deborah G.; Poland, Therese M.; Heyd, Robert L. 2007. Detection and monitoring of emerald ash borer populations: trap trees and the factors that may influence their effectiveness. In: Gottschalk, Kurt W., ed. Proceedings, 17th U.S. Department of Agriculture interagency research forum on gypsy moth and other invasive species 2006; Gen. Tech. Rep. NRS-P-10. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 93.

Research Participants

Principal Investigators

• Deborah G. McCullough, Michigan State University
• Therese Poland, USDA Forest Service - Northern Research Station Research Entomologist

Research Partners

• Andrea Anulewicz, Michigan State University
• David Cappaert, Michigan State University