|PETRICE, TOBY - Michigan State University|
|BAUER, LEAH - Michigan State University|
|POLAND, THERESA - Michigan State University|
|CHANDLER, JENNIFER - University Of Massachusetts, Amherst|
|CRANDALL, TYAN - University Of Massachusetts, Amherst|
|ELKINTON, JOSEPH - University Of Massachusetts, Amherst|
|VAN DRIESCHE, ROY - University Of Massachusetts, Amherst|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2023
Publication Date: 8/1/2023
Citation: Duan, J.J., Schmude, J.M., Petrice, T., Bauer, L.S., Poland, T., Chandler, J., Crandall, T., Elkinton, J.S., Van Driesche, R. 2023. Successful establishment, spread, and impact of the introduced parasitoid spathius galinae (Hymenoptera: Braconidae) on emerald ash borer (Coleoptera: Buprestidae) populations in post-invasion forests in Michigan. Journal of Economic Entomology. https://doi.org/10.1093/jee/toad149.
Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest that has killed millions of ash trees in the U.S. A new parasitic wasp (Spathius galinae) attacking EAB larvae in the Russian Far East was introduced to the U.S. in 2015 for biocontrol of the pest. A field study conducted from 2015 to 2020 showed that introduction of this wasp in post-EAB invasion forests in Michigan, along with the local natural enemies (including previously introduced natural enemies from China), successfully suppressed the invasive EAB populations by 35 – 55% to low densities that may allow surviving ash trees to recover.
Technical Abstract: Spathius galinae Belokobylskij & Strazanac is a larval parasitoid native to the Russian Far East that was introduced to the United States in 2015 for biological control of emerald ash borer, Agrilus planipennis Fairmaire, an invasive beetle responsible for widespread ash mortality. From 2015 to 2017, 1,340 – 1,445 females of S. galinae along with males were released into each study plot, paired with a non-release plot, at six post-invasion forests in three counties (Ingham, Gratiot, and Shiawassee) in southern Michigan. By 2018, S. galinae spread to all six control plots. Based on the year of the first S. galinae parasitism detection from trees in each control plot and the distances of those trees to all the parasitoid release points across the six different forests, we estimated that S. galinae spread at an average (± SE) rate of 10.4 (± 0.3) km per year after its initial releases in 2015. The proportion of sampled trees with S. galinae parasitism, the parasitoid density within sampled trees, and rate of parasitism among host larvae all increased sharply in both control and release plots after the last field releases in 2017, with the highest parasitism levels in 2020. Life table analysis showed that S. galinae alone reduced the pest’s net population growth rate from 2018 to 2020 by 35 – 55% across sites. These results demonstrate that S. galinae has firmly established an increasing population in southern Michigan and now plays a significant role in reducing emerald ash borer populations in the area.