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Forests 2018, 9(10), 659; https://doi.org/10.3390/f9100659

Comparing Methods for Monitoring Establishment of the Emerald Ash Borer (Agrilus planipennis, Coleoptera: Buprestidae) Egg Parasitoid Oobius agrili (Hymenoptera: Encyrtidae) in Maryland, USA

1
Department of Entomology, University of Maryland, 4112 Plant Sciences Building, College Park, MD 20742, USA
2
Beneficial Insects Introduction Research Unit, United States Department of Agriculture—Agricultural Research Service, 501 South Chapel Street, Newark, DE 19711, USA
Current address: Vermont Law School, 164 Chelsea Street, South Royalton, VT 05068, USA.
*
Author to whom correspondence should be addressed.
Received: 18 September 2018 / Revised: 19 October 2018 / Accepted: 19 October 2018 / Published: 22 October 2018
(This article belongs to the Special Issue Impacts, Monitoring and Management of Forest Pests and Diseases)
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Abstract

The emerald ash borer, Agrilus planipennis Fairmaire (EAB), is an invasive beetle that has caused widespread mortality of ash trees in North America. To date, four parasitoids have been introduced in North America for EAB biological control, including the egg parasitoid Oobius agrili Zhang & Huang (Hymenoptera: Encyrtidae). Monitoring EAB egg parasitism is challenging because female beetles oviposit in bark crevices and EAB eggs and O. agrili are small (<1 mm in diameter). Consequently, multiple methods have been developed to recover this parasitoid. Here we compared two methods, visual surveys and bark sifting, used to monitor establishment of O. agrili in Maryland, USA. From 2009 to 2015, a total of 56,176 O. agrili were released at 32 sites across the state. In 2016, we surveyed nine of the study sites for O. agrili establishment using both methods. We compared the amount of time spent searching for eggs separately in each method, and also analyzed the effects of years-post release, total number of parasitoids released, and median month of release, on percent parasitism of EAB eggs, and the percentage of trees per site with parasitized EAB eggs. We found that visually surveying ash trees for EAB eggs was more efficient than bark sifting; the percent parasitism observed using the two methods was similar, but visually surveying trees was more time-efficient. Both methods indicate that O. agrili can successfully establish populations in Maryland, and June may be the best month to release O. agrili in the state. Future research should investigate EAB phenology in the state to help optimize parasitoid release strategies. View Full-Text
Keywords: ash trees; biological control; Buprestidae; Encyrtidae; invasive species ash trees; biological control; Buprestidae; Encyrtidae; invasive species
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Jennings, D.E.; Duan, J.J.; Shrewsbury, P.M. Comparing Methods for Monitoring Establishment of the Emerald Ash Borer (Agrilus planipennis, Coleoptera: Buprestidae) Egg Parasitoid Oobius agrili (Hymenoptera: Encyrtidae) in Maryland, USA. Forests 2018, 9, 659.

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