Effect of microhabitats and seasonal conditions on the supercooling points of Tetrastichus planipennisi in Vermont

Authors: NI, GEORGE - University Of Vermont; GOTELLI, NICHOLAS - University Of Vermont; Duan, Jian

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2026
Publication Date: 2/2/2026
Citation: Ni, G., Gotelli, N., Duan, J.J. 2026. Effect of microhabitats and seasonal conditions on the supercooling points of Tetrastichus planipennisi in Vermont. Biological Control. https://doi.org/10.1007/s10526-026-10382-0.
DOI: https://doi.org/10.1007/s10526-026-10382-0

Interpretive Summary: The parasitic wasp (Tetrastichus planipennisi) is an important natural enemy introduced to the United States for biological control of the invasive emerald ash borer (EAB). Since it was introduced to the United States in 2007 from Asia, this parasitoid wasp has been released in 32 States for EAB biocontrol. In the present study, we determined how local environment and seasonality affect the cold tolerance of this introduced natural enemy for overwintering survival. Our findings indicate that the cold tolerance of this natural enemy is affected by the insect’s exposure to the minimum and/or maximum ambient temperatures of the local environment as well as seasonality. Thus, local environmental conditions and seasonality can have significant impacts on the overwintering survival of this biocontrol agent in more Northerly regions.

Technical Abstract: Biological control programs often need to take into consideration a wide array of biotic and abiotic factors that affect the success and establishment of their biocontrol agents. As biocontrol agents are often deployed in regions with novel environmental climates, their supercooling points (SCP), which indicates the lowest temperature at which their bodily fluids can remain liquid prior to freezing, plays a vital role in determining their overwintering survival and eclosion to adult stage. Tetrastichus planipennisi, a larval endoparasitoid of the emerald ash borer (Agrilus planipennisi), was introduced in 2007 from China to the United States for biocontrol of the invasive emerald ash borer (Agrilus planipennis Fairmaire) and has since been released as a biocontrol agent in over 32 U.S. states accross a large latitudinal gradient. Previous studies have demonstrated that the successful establishment of T. planipennisi is affected by extremely low temperature weather during winter seasons. In this study, we conducted a field-based experiment during the winter of 2020-2021 across three plots in Jericho Research Forest in Vermont, US, to determine if we could observe SCP change over time of first instar larvae of T. planipennisi. We housed T. planipennisi larvae in jars and used artificial shelters to manipulate the temperature profiles experienced by T. planipennisi over the winter season. We found that across the study period, control groups had SCP values 0.41 degrees Celsius lower than treatment groups, with the largest difference in February where mean SCP of control groups were 5.1 degrees Celsius lower than sheltered groups. SCP had a significant positive linear correlation with mean minimum temperatures for the unsheltered control group (P= 0.028, slope = 1.29 ± 0.54, intercept = -20.37 ± 2.39 SE). Our findings provide strong evidence that changes in the minimum temperatures experienced by T. planipennisi can result in adjusted SCPs and increased vulnerability to polar vortexes and extreme temperature shifts. This study demonstrates the need to consider local environment and microhabitat conditions when investigating biocontrol release sites against the EAB in North America as they can have significant impacts on the overwintering survival of the biocontrol agents in more Northerly regions.