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ARS Home » Northeast Area » Newark, Delaware » Beneficial Insects Introduction Research Unit » Research » Publications at this Location » Publication #304393
Title: Long-term monitoring of the introduced emerald ash borer (Coleoptera: Buprestidae) egg parasitoid, oobius agrili (Hymenoptera: Encyridae), in Michigan, USA and evaluation of a newly developed monitoring technique

Author
item ABELL, KRISTOPHER - University Of Massachusetts
item BAUER, LEAH - Forest Service (FS)
item Duan, Jian
item VAN DRIESCHE, ROY - University Of Massachusetts

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2014
Publication Date: 8/12/2014
Citation: Abell, K.J., Bauer, L.S., Duan, J.J., Van Driesche, R. 2014. Impact of the introduced egg parasitoid Oobius agrili (Hymenoptera: Encyrtidae) on Emerald Ash Borer (Coleoptera: Buprestidae) in Michigan, USA. Biological Control. DOI: 10.1016/j.biocontrol.2014.08.002.

Interpretive Summary: Oobius agrili is a parasitic wasp that attacks eggs of the invasive emerald ash borer (EAB), and can be responsible for over half of EAB egg mortality in its native range of northeastern Asia. This parasitic wasp has been introduced as a biological control agent of this pest in Michigan and throughout the infested area of the United States. In this study, we evaluated the impact of this beneficial wasp over six years (2007-2012) in field plots in Michigan using two methods for measuring parasitism of emerald ash borer eggs: (1) timed visual searches of bark on standing ash trees and (2) bark collection and sieving. Both methods confirmed the establishment of this biological control agent and its dispersal into control plots. Data from the visual search method, suggested that parasitism in release plots remained low for the first five years post-release and rose in the sixth year. The bark sieving method suggested that rates of parasitism were much higher in release plots for the two years in which both methods were applied. These findings indicate that the impact of this beneficial wasp on EAB populations is increasing and may now become an important source of mortality for EAB populations. We recommend the bark sieving method as the more effective method to estimate parasitism rates of this beneficial wasp.

Technical Abstract: Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a serious invasive pest of ash trees (Fraxinus spp.) in North America. The egg parasitoid Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) was introduced as a biological control agent of this pest in Michigan and throughout the infested area of the United States. A critical component of any biological control program is post-release monitoring and evaluation; however, because of the small size and cryptic nature of O. agrili, evaluation of its impact is difficult. We evaluated the impact of O. agrili over six years (2007-2012) in field plots in Michigan. We compared two methods for measuring parasitism of emerald ash borer eggs: (1) timed visual searches of bark on standing ash trees and (2) bark collection and sieving. Both methods were carried out in parasitoid release and control plots, the visual method for all six years, but the bark collection method for the last two years only. Both methods confirmed the establishment of O. agrili and its dispersal into control plots. Data from the visual search method, suggested that parasitism in release plots remained low (0.7-4.2%) for the first five years post-release and rose in the sixth year to 10.6%. The bark sieving method suggested that rates of parasitism were much higher in release plots for the two years in which both methods were applied, being 21.8% in 2011 and 18.9% in 2012. These findings indicate that the population-level impact of O. agrili is increasing and may now be an important source of mortality for EAB populations. We recommend the bark sieving method as the more effective method to estimate parasitism rates of O. agrili.