Determining optimal parasitoid release timing for the biological control of emerald ash borer (Coleoptera: Buprestidae)

Authors: ABELL, KRISTOPHER - University Of Maryland; Duan, Jian; SHREWSBURY, PAULA - University Of Maryland

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2019
Publication Date: 12/1/2019
Citation: Abell, K.J., Duan, J.J., Shrewsbury, P.M. 2019. Determining optimal parasitoid release timing for the biological control of emerald ash borer (Coleoptera: Buprestidae). Florida Entomologist. 102(4):691-694. https://doi.org/10.1653/024.102.0403.
DOI: https://doi.org/10.1653/024.102.0403

Interpretive Summary: Emerald ash borer (EAB) is one of the most destructive invasive forest pests in North America, where it is responsible for the death of hundreds of millions of ash trees. A classical biological control program was initiated against this invasive beetle in the US in 2007. This involves the introduction and establishment of several natural enemies from the pest's native range in China. Timing the release of the introduced natural enemies to coincide with the presence of susceptible stages of the pest is critical for the success and cost-effectiveness of the biological control program. With University of Maryland cooperators, we conducted periodic field surveys of EAB phenology in central Maryland by using green funnel traps to sample adults and debarking of infested ash trees to sample larval stages. Our results suggest that EAB egg parasitoid releases should occur from mid May to late June and larval parasitoid releases should occur between mid July and mid-August.

Technical Abstract: The emerald ash borer (EAB), Agrilus planipennis Fairmaire, quickly established itself as an invasive species in North America since it was first detected near Detroit, Michigan in 2002. Just one year later, EAB was accidentally introduced to Maryland on imported ash nursery stock. After quarantine and eradication efforts failed, a classical biological control program was initiated in Maryland in 2009 with the release of two larval parasitoids Tetrastichus planipennisi Yang and Spathius agrili Yang, and one egg parasitoid, Oobius agrili Zhang and Huang. Critical to the success, efficiency, and cost-effectiveness of classical biological control programs is timing the release of parasitoids to coincide with the time that susceptible stages of the host are present. In 2017, periodic field surveys at two sites in central Maryland were conducted to assess EAB phenology using green funnel traps to sample adults and debarking infested ash trees to sample larval stages. Adult EAB first appeared in traps on May 18 (862 Growing Degree Day at base 10oC (GDD10)), peaked on June 15 (1481 GDD10) and were absent from July 13 (2342 GDD10) through October 12 (4669 GDD10) when surveys were terminated. Larval sampling in early August (3056 GDD10) found all larval instars present, the most common being 2nd instar (46%), followed by 3rd instar (28%), 4th instar (20%), 1st instar (5%), and J-larva (0.5%). Larval sampling in late October (4878 GDD10) found J-larvae to be the dominant stage present (92.2%), followed by 4th instar (4.8%), 3rd instar (2.4%), and 2nd instar (0.6%). We found that EAB was univoltine, and that nearly 50% of EAB larvae had developed to stages susceptible to parasitism (3rd and 4th instar) by early August (3056 GDD10). By late October (4878 GDD10) 92% had developed beyond parasitoid susceptible stages (J-larvae). These findings suggest that egg parasitoid releases are best targeted from early May to late June at an approximate GDD10 range of 600 and 2200, and larval parasitoid releases are best targeted approximately between 2500 and 4500 GDD10.