Abstract
Emerald ash borer (EAB),
Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a serious invasive pest of ash trees (
Fraxinus spp.) in North America from China. The egg parasitoid
Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) was introduced from China as a biological control agent for 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 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, sifting, and sorting. Both methods were carried out in paired parasitoid-release and control plots, the visual search method over a six-year period (2008-2013) and the more recently developed bark-collection and sifting method for 2 years (2012-2013). The visual search method found parasitism in release plots remained low (0.7-4.2%) in samples taken from 2008 to 2012 and reached 10.6% in 2013. In comparison, the bark-sifting method found that rates of egg parasitism were considerably higher in release plots, 21.8% and 18.9% for samples taken in 2012 and 2013, respectively. These findings indicate that the population-level impact of
O. agrili is increasing and may be an important source of mortality for EAB populations. We recommend the bark-collection and sifting method as the more effective method to recover parasitoids and estimate parasitism rates of
O. agrili.
Keywords
Invasive species,
Parasitoid release and recovery,
Natural enemy introduction,
Parasitoid recovery methods
Citation
Abell, Kristopher J.; Bauer, Leah S.; Duan, Jian J.; Van Driesche, Roy. 2014. Long-term monitoring of the introduced emerald ash borer (Coleoptera: Buprestidae) egg parasitoid, Oobius agrili (Hymenoptera: Encyrtidae), in Michigan, USA and evaluation of a newly developed monitoring technique. Biological Control. 79: 36-42.
