Spread and phenology of Spathius galinae Belokobylskij & Strazenac (Hymenoptera: Braconidae) and Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae)

Authors: QUINN, NICOLE - University Of Massachusetts; GOULD, JULI - Animal And Plant Health Inspection Service (APHIS); RUTLEDGE, CLAIRE - Agricultural Experiment Station, Connecticut; FASSLER, ALIZA - Animal And Plant Health Inspection Service (APHIS); ELKINTON, JOSEPH - University Of Massachusetts, Amherst; Duan, Jian

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2021
Publication Date: 11/14/2021
Citation: Quinn, N.F., Gould, J.S., Rutledge, C.E., Fassler, A., Elkinton, J.S., Duan, J.J. 2021. Spread and phenology of Spathius galinae Belokobylskij & Strazenac (Hymenoptera: Braconidae) and Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae). Biological Control. 165:1-7. https://doi.org/10.1016/j.biocontrol.2021.104794.
DOI: https://doi.org/10.1016/j.biocontrol.2021.104794

Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest that has killed millions of ash trees in the U.S. Two parasitic wasps attacking EAB larvae in Asia were introduced to the U.S. for biocontrol of the pest between 2007 and 2015. We determined their seasonal occurrence and spread in New York and Connecticut. Our findings indicate that the biological control program has produced an abundant natural enemy population that has been spreading widely and attacking EAB throughout the growing season. Future release efforts may allow for wider seasonal timing and spacing of release sites across geographic regions.

Technical Abstract: Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive wood-boring pest of ash trees (Fraxinus spp.) in the US. It is responsible for catastrophic decline of ash in urban and forested ecosystems, resulting in millions of dollars in economic losses. Biological control is one of the most promising management options available to reduce A. planipennis spread and impact. From 2015 to 2017, two larval parasitoids of A. planipennis from its native range, Spathius galinae Belokobylskij & Strazenac (Hymenoptera: Braconidae) and Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), were released in forested areas in New York and Connecticut. The purpose of this study was to measure the spread and phenology of these introduced parasitoids. From May to September 2020, sentinel ash logs containing EAB larvae were deployed in naturally occurring A. planipennis infested trees at each release site and in 2 km intervals up to 14 km away from the release site. Logs were replaced every two weeks and the parasitization rate was recorded. Each month, three trees from each release area were also cut and debarked to record A. planipennis infestation levels, natural parasitization rates, and A. planipennis and parasitoid phenology. We observed that both S. galinae and T. planipennisi emerged from the logs first deployed from the end of May to early June. Parasitization peaked in late July and mid-August, with sentinel logs deployed at each distance producing both species throughout the summer until mid-September. Both S. galinae and T. planipennisi were detected 14 km away from the release sites, the greatest distance away from the release sites sampled. Debarked trees produced similar seasonal patterns of parasitism. Our results indicate that the classical biological control program initiated several years ago has successfully produced a self-sustaining population of both S. galinae and T. planipennisi, which has been spreading widely and attacking the borer throughout the growing season. These findings strongly suggest that future release efforts may allow for wider temporal release windows and larger strategic spacing of release points across geographic regions.