|CHANDLER, JENNIFER - University Of Massachusetts, Amherst|
|ELKINTON, JOSEPH - University Of Massachusetts, Amherst|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2020
Publication Date: 6/11/2020
Citation: Chandler, J., Elkinton, J.S., Duan, J.J. 2020. Induction of cold hardiness in Spathius galinae (Hymenoptera: Braconidae), a larval parasitoid introduced for biocontrol of emerald ash borer in North America. Biological Control. https://doi.org/10.1016/j.biocontrol.2020.104343.
Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest that has currently spread to 35 U.S. states. A biocontrol agent (Spathius galinae, a parasitic wasp) collected from the pest's native home (Russian Far East) has been approved for releases against EAB in the U.S. and Canada since 2015. We evaluated the ability of this introduced biocontrol agent to survive below-freezing temperatures at different field locations representing a gradient of wintering temperatures (or hardness zones) from December to March in Northeastern U.S. Our data provide strong evidence that this EAB biocontrol agent can increase its cold hardness in response to below-freezing temperatures. This ability will allow us to determine the optimal geographic range for field releases against EAB in North America.
Technical Abstract: The ability of a biocontrol agent to acclimate to and survive the climate of intended introduction locations is a critical attribute for successful biological control of invasive exotic species. We tested induction of cold tolerance of Spathius galinae Belokobylskij & Strazanac, a braconid parasitoid native to the Russian Far East, introduced to the United States for biocontrol of the ash (Fraxinus spp.) pest, emerald ash borer (EAB), Agrilus planipennis Fairmaire, by measuring the supercooling point (SCP) of mature S. galinae larvae exposed to winter temperatures at four different field locations that span a gradient of plant hardiness zones. We observed a significant effect of overwinter location on SCPs of S. galinae larvae collected from field populations with lower SCPs observed at locations with lower minimum ambient temperatures. We also tested SCP of three stages (early instar, late instar, and mature cocooned larvae) of lab-reared parasitoids and found that SCP did not significantly differ between stages of lab-reared S. galinae. Our findings provide strong evidence that S. galinae can reduce SCP in response to below-freezing temperatures. The increase in cold hardiness of S. galinae in response to below-freezing temperatures should be considered in delineation of the optimal geographic range for biocontrol releases against EAB in North America.