|Bauer, Leah - Us Forest Service (FS)|
|Hansen, Jason - Michigan State University|
|Abell, Kristopher - University Of Massachusetts|
|Van Driesche, Roy - University Of Massachusetts|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2011
Publication Date: 3/1/2012
Citation: Duan, J.J., Bauer, L.S., Hansen, J.A., Abell, K.J., Van Driesche, R. 2012. An improved method for monitoring parasitism and establishment of Oobius agrili (Hymenoptera: Encyrtidae) an egg parasitoid introduced for biological control of the emerald ash borer (Coleoptera: Buprestidae) in North America. Biological Control. 60(3):255-261. DOI: 10.1016/j.biocontrol.2011.11.007.
Interpretive Summary: The parasitic wasp, Oobius agrili, is one of three natural enemies from Asia currently being released in the United States to control the emerald ash borer (EAB), an invasive insect that has destroyed millions of ash trees in the U.S. This wasp attacks eggs of EAB, which are laid in bark crevices or under loose bark flakes of ash limbs or trunks. In this study, we describe a monitoring method developed using ash logs with freshly laid EAB eggs, which are hung on the trunks of ash trees to determine the effectiveness of this beneficial wasp following field release. Findings from our study showed that our method successfully detected parasitism by this beneficial wasp immediately following field release, as well as the year following field release. The method will be useful to determine the establishment, dispersal and population impact of this parasitic wasp on the targeted EAB.
Technical Abstract: Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) is a solitary egg parasitoid that is being released in the United States for biological control of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Field and laboratory trials with “sentinel ash logs” infested with EAB eggs were conducted in Michigan between 2009 and 2010 to monitor the parasitism and establishment of O. agrili. In addition, naturally occurring EAB eggs were collected in both parasitoid-release and control plots to compare with the EAB egg-sentinel log technique. While no EAB eggs were attacked by O. agrili on the sentinel logs deployed in the non-parasitoid release control plots, >50% sentinel logs deployed in the parasitoid-release plots had one or more O. agrili- parasitized eggs (3.9 – 48.2% egg parasitism) after field exposure. In the laboratory, 100% of EAB egg-sentinel logs exposed to O. agrili inside rearing jars for one week had one or more parasitized eggs (68.5% egg parasitism). There were no consistent relationships between the percent parasitism by O. agrili and host egg density on the sentinel logs, either in laboratory or field trials; however, there was a significantly positive linear relationship between the number of EAB eggs parasitized by O. agrili and the egg density of the logs in both laboratory and field tests. Deployment of EAB egg-sentinel logs detected low levels of parasitism by O. agrili in all three ash stands where O. agrili was released in previous years. In contrast, collection of naturally occurring EAB eggs detected the parasitism in only one of these three parasitoid-release ash stands. No parasitism was detected in control ash stands with either method. These findings indicate that populations of O. agrili released in 2009 or earlier (2007 or 2008) had successfully overwintered and established in the released ash stands by 2010, but had not yet dispersed to the control stands.