Factors affecting the yellow pan captures of the larval parasitoids for biocontrol of emerald ash borer: implications for monitoring parasitoid establishment and seasonal abundance

Authors: PETRICE, TOBY - Us Forest Service (FS); POLAND, THERESE - Us Forest Service (FS); BAUER, LEAH - Us Forest Service (FS); STRAZANAC, JOHN - Us Forest Service (FS); Schmude, Jonathan; Duan, Jian; RAVLIN, WILLIAM - Michigan State University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2023
Publication Date: 5/25/2023
Citation: Petrice, T.R., Poland, T.M., Bauer, L.S., Strazanac, J.S., Schmude, J.M., Duan, J.J., Ravlin, W.F. 2023. Factors affecting the yellow pan captures of the larval parasitoids for biocontrol of emerald ash borer: implications for monitoring parasitoid establishment and seasonal abundance. Biological Control. https://doi.org/10.1016/j.biocontrol.2023.105272.
DOI: https://doi.org/10.1016/j.biocontrol.2023.105272

Interpretive Summary: The emerald ash borer (EAB), accidentally introduced to the U.S. from Asia in the 1990s, is a serious invasive forest pest killing millions of North American ash trees. Four natural enemies (parasitoids) from Asia were introduced to North America for EAB biocontrol between 2007 and 2015. We evaluated yellow pan traps as a monitoring tool in capturing the EAB parasitoids in Michigan, where two introduced wasps (Tetrastichus planipennisi and Spathius galinae) have established populations. Yellow pan traps captured both EAB parasitoids throughout the growing season, although capture numbers and rates were low. Tree size and parasitized EAB larval densities were related to parasitoid adult captures. These findings will help to improve yellow pan trap efficacy in monitoring the establishment and abundance of EAB larval parasitoids.

Technical Abstract: Yellow pan traps are frequently used to monitor establishment of hymenopteran parasitoids introduced for biological control of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). To evaluate and improve their efficacy as a monitoring tool, we conducted field studies during 2016-2019 in southern Michigan where the introduced hymenopteran larval parasitoids, Tetrastichus planipennisi Yang (Eulophidae) and Spathius galinae (Braconidae) Belokobylskij & Strazanac were established. Our objectives were to describe parasitoid seasonal abundance, identify host tree variables that might influence parasitoid capture numbers (i.e., number of adults captured) and capture rates (i.e., number of positive traps), and compare parasitoid trap captures to parasitized EAB larval densities. Yellow pan trap capture numbers and rates of both species were low for most study sites and years. Captures of both species occurred throughout the growing season and neither showed a consistent trend in seasonal abundance. EAB infested trees that had suppressed or intermediate crown classes had higher T. planipennisi capture numbers and rates than dominant or co-dominant crown classes. During some years, T. planipennisi capture rates increased with decreasing tree diameters and T. planipennisi capture numbers increased with increasing numbers of epicormics sprouts on host trees. Spathius galinae captures had no significant relationship with host tree variables, but low overall capture numbers may have prevented detection of any relationships. Tetrastichus planipennisi adult capture numbers were significantly correlated with the previous year’s densities of T. planipennisi parasitized larvae dissected from trees. Spathius galinae capture numbers were not correlated with parasitized EAB larval densities. We discuss the relevance of our findings to the improvement of yellow pan trap efficacy for monitoring the establishment and seasonal abundance of introduced EAB larval parasitoids.