Forecasting overwintering mortality of Spathius galinae in North America

Jacob T. Wittman, Brian H. Aukema, Jian J. Duan, Robert C. Venette

Research output: Contribution to journalArticlepeer-review

Abstract

Evaluating the cold tolerance of biological control agents is often necessary to optimize their release and performance. We used field and laboratory assays to determine the cold hardiness of the parasitoid Spathius galinae Belokobylskij & Strazanac, an approved classical biological control agent of emerald ash borer (Agrilus planipennis Fairmaire) in North America. Supercooling points and lower lethal temperature of mature (cocooned) S. galinae larvae were measured in controlled cooling assays in the laboratory. Most S. galinae larvae died after reaching their supercooling point, which occurred at −25.0 °C on average. Several larvae, however, initiated freezing but later eclosed, suggesting S. galinae may be partially freeze tolerant. Supercooling points were not affected by chilling rate. In the winter of 2019 – 2020, we monitored development of mature S. galinae larvae in ash segments above and beneath the snow in three locations in Minnesota, USA. Nearly 100% of S. galinae larvae died after air temperatures reached −29 °C in Minnesota. Using models developed from our data, we forecast eclosion rates of S. galinae based on minimum winter temperatures across the range of ash (Fraxinus spp.) in North America. Our results indicate that S. galinae populations may suffer high overwintering mortality in areas where winter temperatures regularly decrease below −28 °C, but a small portion of the population may be able to survive lower temperatures.

Original languageEnglish (US)
Article number104694
JournalBiological Control
Volume160
DOIs
StatePublished - Sep 2021

Bibliographical note

Funding Information:
The findings and conclusions in this publication are those of the authors and should not be construed to represent any official USDA or U.S. Government determination of policy. Funding was provided by an appropriation from the Environmental and Natural Resources Trust Fund overseen by the Legislative Citizen’s Commission on Minnesota Resources Project M.L. 2017 Chpt. 96 Subd. 06-066. We thank Aubree Kees, Becca Robertson, Pheylan Anderson, Alexa Koch, and Patrick Perish for help rearing parasitoids, carrying out laboratory assays, and peeling ash sticks. Marie Hallinen provided comments on previous drafts of this manuscript. Three anonymous reviewers provided valuable feedback that improved an earlier version of this work.

Funding Information:
The findings and conclusions in this publication are those of the authors and should not be construed to represent any official USDA or U.S. Government determination of policy. Funding was provided by an appropriation from the Environmental and Natural Resources Trust Fund overseen by the Legislative Citizen's Commission on Minnesota Resources Project M.L. 2017 Chpt. 96 Subd. 06-066. We thank Aubree Kees, Becca Robertson, Pheylan Anderson, Alexa Koch, and Patrick Perish for help rearing parasitoids, carrying out laboratory assays, and peeling ash sticks. Marie Hallinen provided comments on previous drafts of this manuscript. Three anonymous reviewers provided valuable feedback that improved an earlier version of this work. The data and code used to produce these results are available on DRUM (Data Repository for the University of Minnesota) (Wittman et al. 2021).

Publisher Copyright:
© 2021 Elsevier Inc.

Keywords

  • Agrilus planipennis
  • Cold tolerance
  • Eclosion
  • Emerald ash borer
  • Parasitoid
  • Supercooling

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