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Emerald Ash Borer

Biological Control of the Emerald Ash Borer

Research Issue

In 2002, the emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), an Asian beetle that feeds on ash trees (Fraxinus spp.), was discovered as the cause of widespread ash tree mortality in southeast Michigan and nearby Ontario.  The results of subsequent studies showed that EAB was inadvertently introduced near Detroit, Michigan during the 1990s from northeast China, probably in EAB-infested solid-wood packing materials used in international trade.  Despite federal and state quarantines that restricts the movement of ash out of infested areas, EAB continues spreading in the U.S. and eastern Canada.  Although this beetle spreads naturally by flying short distances, long-distance spread is caused by people moving EAB-infested ash firewood, nursery stock, and timber.  The rapid expansion of the EAB infestation across a wide range of climate zones suggests that this invasive beetle will continue spreading throughout the continent. (See USDA APHIS Cooperative Emerald Ash Borer Project Map of Initial county EAB detections in North America.)

The spread of EAB in North America puts our 16 native ash species and the organisms dependent on these trees at risk.  Ash species in our forests already devastated by the EAB invasion are:  white ash (F. americana), green ash (F. pennsylvanica), black ash (F. nigra), blue ash (F. quadrangulata), pumpkin ash (F. profunda), and Carolina ash (F. caroliniana).  Each species is adapted to different sites in our forests,with many adapted to sensitive wetland and riparian habitats.  Before the arrival of EAB, ash trees were also important economically with 8 billion ash trees on U.S. timberlands valued at $282.25 billion.  Sustainable methods to manage EAB in forested ecosystems generally involve the use of classical biological control or biocontrol.

Biological control or “biocontrol" is a long-term management strategy used throughout the world for sustained control of invasive pests.  This approach is generally limited to such pests that have been established for more than five years, cannot be eradicated, and cause significant ecological, environmental, or economic damage.  Biocontrol involves studying the biology of the pest, determining countries where it is native, and “foreign exploration” in those countries for host specific natural enemies.  Suitable natural enemies are often insect parasitoids or predators that coevolved with the target invasive pest in its native range.  In the U.S., permits for the introduction of host-specific natural enemies or “biocontrol agents” may be granted by USDA APHIS PPQ (APHIS) after completion of extensive research on 1) the biology and host range of each natural enemy in U.S. quarantine laboratories and in countries of origin; 2) risk benefit analyses including potential non-target impacts; 3) consensus by North American experts; 4) posting of an Environmental Assessment on the Federal Register for public comment; and 5) state concurrence.

EAB Research and the EAB Biocontrol Program
Biocontrol of EAB began in the U.S. in 2007 when APHIS issued permits for the environmental release of three hymenopteran parasitoid species of EAB from China to EAB-infested ash stands in southern Michigan.  These EAB biocontrol agents are:  an egg parasitoid, Oobius agrili (Encyrtidae) (Fig.1) and two larval parasitoids, Tetrastichus planipennisi (Eulophidae) (Fig. 2) and Spathius agrili (Braconidae) (Fig. 3).  In 2015, another EAB larval parasitoid, Spathius galinae (Braconidae) (Fig. 4) from the Russian Far East, was approved for release because S. agrili did not establish in northern regions.

Research Results

Due to the long life cycle of trees and the large number of ash trees and species throughout North America, it will be many years before we know if biocontrol can protect ash species against EAB.  But there are some encouraging research results from study sites in Michigan where parasitoid releases began in 2007.  These results show the establishment and spread of T. planipennisi and O. agrili attacking EAB in surviving green, white, and black ash saplings and trees. Moreover, reductions in EAB densities following parasitoid releases were correlated with increased parasitism, first by native larval parasitoids [mainly Phasgonophora sulcata (Chalcididae) (Fig. 5) and Atanycolus spp.(Braconidae) (Fig. 6)] when EAB densities were high, then by the introduced parasitoids T. planipennisi and O. agrili as EAB densities declined. Although it is too soon to confirm sustained establishment of S. galinae, which was first released in 2015 at these sites, both its prevalence and distribution have steadily increased.  The combined mortality of EAB caused by woodpeckers, the native and introduced parasitoids, intraspecific competition, disease, innate tree defenses, and reduced ash abundance contributed to the collapse of EAB populations in this region. 

Tree inventories at the Michigan study sites found low numbers of large ash trees survived, while the numbers of ash sprouts, saplings, and small to medium trees are increasing.  As these ash trees mature, researchers will continue to monitor the impacts that the EAB biocontrol agents and other mortality factors have on EAB population densities and ash health.

Expected Outcomes

Researchers remain optimistic that the combined impacts of native and introduced natural enemies and tree resistance will regulate EAB population dynamics sufficiently to allow for the survival and reproduction of certain ash genotypes in forested areas of North America.


Oobius agrili-Solitary, egg parasitoid. Photo credit: D. Miller.
Fig. 1. Oobius agrili – Solitary parasitoid of EAB eggs introduced from China.  Photo credit: D. Miller
Tetrastichus planipennisi - Gregarious, larval endoparasitoid.  Photo credit: D. Cappaert.
Fig. 2. Tetrastichus planipennisi – Gregarious endoparasitoid of EAB larvae introduced from China.  Photo credit: D. Cappaert
Spathius galinae - gregarious, larval ectoparasitoid.  Photo credit: T. Petrice.
Fig. 3. Spathius agrili – Gregarious ectoparasitoid of EAB larvae introduced from China.  Photo credit: J. Duan
Spathius galinae - gregarious, larval ectoparasitoid.  Photo credit: T. Petrice.
Fig. 4. Spathius galinae – Gregarious ectoparasitoid of EAB larvae introduced from the Russian Far East.  Photo credit: T. Petrice
Phasgonophora sulcata - Native, solitary, endoparasitoid. Photo credit: D. Miller.
Fig. 5. Phasgonophora sulcata – Solitary endoparasitoid of buprestid larvae in North America.  Photo credit: D. Miller
Atanycolus sp. - Native, solitary, endoparasite. Photo credit: H. Liu.
Fig. 6. Atanycolus spp. – Solitary ectoparasitoid of wood-boring beetle larvaein North America.  Photo credit: H. Liu


Research Results

Selected Publications

See a more comprehensive listing on our EAB publications page and the publications listing at

Duan, Jian J.; Bauer, Leah S.; Van Driesche, Roy G.; Gould, Juli R. 2018. Progress and challenges of protecting North American ash trees from the emerald ash borer using biological control. Forests. 9(3): 142; doi:10.3390/f9030142

Kashian, Daniel; Bauer, Leah; Spei, Benjamin; Duan, Jian; Gould, Juli. 2018. Potential Impacts of Emerald Ash Borer Biocontrol on Ash Health and Recovery in Southern Michigan. Forests , 9, 296; doi:10.3390/f9060296 

Duan, Jian J.; Bauer, Leah S.; Van Driesche, Roy G. 2017. Emerald ash borer biocontrol in ash saplings: The potential for early stage recovery of North American ash trees. Forest Ecology and Management. 394: 64-72.

Duan, Jian J.; Van Driesche, Roy G.; Bauer, Leah S.; Reardon, Richard; Gould, Juli; Elkinton, Joseph S. 2017. The role of biocontrol of emerald ash borer in protecting ash regeneration after invasion. FHAAST-2017-02. Morgantown, WV: U.S. Department of Agriculture, Forest Service, Forest Health Assessment and Applied Sciences Team. 10 p.

Margulies, Elan; Bauer, Leah; Ibáñez, Inés. 2017. Buying Time: Preliminary Assessment of Biocontrol in the Recovery of Native Forest Vegetation in the Aftermath of the Invasive Emerald Ash Borer. Forests. doi:10.3390/f8100369

Bauer, Leah S.; Duan, Jian J.; Gould, Juli R.; Van Driesche, Roy. 2015. Progress in the classical biological control of Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) in North America. The Canadian Entomologist. 147(3): 300-317.

Duan, Jian J.; Bauer, Leah S.; Abell, Kristopher J.; Ulyshen, Michael D.; Van Driesche, Roy G. 2015. Population dynamics of an invasive forest insect and associated natural enemies in the aftermath of invasion: implications for biological control. Journal of Applied Ecology. 52(5): 1246-1254.

 Abell, Kristopher J.; Bauer, Leah S.; Duan, Jian J.; Van Driesche, Roy. 2014. Long-term monitoring of the introduced emerald ash borer (Coleoptera: Buprestidae) egg parasitoid, Oobius agrili(Hymenoptera: Encyrtidae), in Michigan, USA and evaluation of a newly developed monitoring technique. Biological Control. 79: 36-42.

Duan, Jian J.; Bauer, Leah S.; Abell, Kristopher J.; Lelito, Jonathan P.; Van Driesche, Roy. 2013. Establishment and abundance of Tetrastichus planipennisi (Hymenoptera: Eulophidae) in Michigan: potential for success in classical biocontrol of the invasive emerald ash borer (Coleoptera: Buprestidae). Journal of Economic Entomology. 106: 1145-1154.

Liu HP, LS Bauer, DL Miller, TH Zhao, RT Gao, LW Song, QS Luan, RZ Jin, CQ Gao. 2007. Seasonal abundance of Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies Oobius agrili (Hymenoptera: Encyrtidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae) in China.  Biological Control 42: 61-71.

Zhang YZ, DW Huang, TH Zhao, HP Liu, LS Bauer.  2005. Two new species of egg parasitoids (Hymenoptera: Encyrtidae) of wood-boring beetle pests from China.  Phytoparasitica 53: 253-260.

Liu HP, LS Bauer, RT Gao, TH Zhao, TR Petrice, RA Haack. 2003. Exploratory survey for the emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae), and its natural enemies in China.  Great Lakes Entomologist 36: 191-204.

EAB Biocontrol Methods

USDA–APHIS/ARS/FS. 2019. Emerald Ash Borer Biological Control Release and Recovery Guidelines. USDA–APHIS–ARS–FS, Riverdale, Maryland. 65 p.

Bauer, Leah; Hansen, Jason; Gould, Juli. 2016. Yellow Pan Traps: A Simple Method for Trapping Larval Parasitoids Released for Biological Control of the Emerald Ash Borer. 3 p. (pdf - You may obtain a free PDF reader from Adobe.)


Research Participants

Principal Investigators

  • Leah S. Bauer, US Forest Service, Northern Research Station Research Entomologist
  • Jian Duan, USDA ARS BIIRU
  • Roy Van Driesche, Department of Environmental Conservation, University of Massachusetts

Research Partners

Last Modified: 06/13/2019

About this Research Area
About Emerald Ash Borer
Selected Studies