|Driesche, Roy van|
Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/10/2010
Publication Date: 2/1/2011
Citation: Duan, J.J., Leah, B., Ulyshen, M., Gould, J., Driesche, R. 2011. Development of methods for the field evaluation of Oobius agrili (Hymenoptera: Encyrtidae) in North America, a newly introduced egg parasitoid of the emerald ash borer (Coleoptera: Buprestidae). Biological Control. 56:170-174. 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 develop a method whereby laboratory-reared “sentinel eggs” are placed under bark flaps to measure the impact of the natural enemy on survivorship of EAB eggs. In addition, we also collected naturally occurring EAB eggs in both the natural enemy release and control plots to measure parasitism. While no parasitism was detected with either sentinel or naturally occurring EAB eggs in control plots in either 2008 or 2009, a low level of parasitism by the natural enemy was detected in the natural enemy release plots in both artificially deployed sentinel eggs and field-collected, naturally occurring eggs. The findings are of value for developing methods for detecting and measuring the impacts of the parasitic wasp.
Technical Abstract: A field study was conducted in forested plots near Lansing, Michigan in 2008 and 2009 to evaluate the newly introduced egg parasitoid, Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae), for control of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). To measure parasitism by O. agrili, laboratory-reared “sentinel EAB eggs” were deployed under bark flaps on trunks of selected ash trees in both parasitoid-release and non-release control plots. In addition, naturally occurring EAB eggs were collected in both parasitoid-release and control plots to measure parasitism. While no parasitism was detected with either sentinel or naturally occurring EAB eggs in control plots in either 2008 or 2009, a low level of parasitism by O. agrili was detected in the parasitoid-release plots in both artificially deployed sentinel eggs (= 0.3%) and field-collected, naturally occurring eggs (0.7 – 4.2%). In addition to losses due to parasitism by O. agrili, a large proportion (35 – 49%) of the field-deployed sentinel eggs disappeared, possibly due to predators such as ants, in both parasitoid-release and control plots. While no statistical differences between parasitoid release and control plots were detected in parasitism and other sources of egg mortality (failure to hatch, and/or disappearance), losses due to parasitism, failure to hatch and/or disappearance varied significantly across study locations in both 2008 and 2009, suggesting that site-to-site variation needs to be considered in future parasitoid evaluation studies. The relevance of these findings to development of methods for detecting and measuring the impacts of egg parasitoids of wood-boring beetles is discussed.