Comparative responses of two congeneric larval parasitoids of emerald ash borer to ambient temperatures: implications for biocontrol introduction

Authors: DANG, YINGQIAO - Chinese Academy Of Forestry; GREEN, MITCHELL - University Of Massachusetts, Amherst; WANG, XIAO-YI - Chinese Academy Of Forestry; Duan, Jian

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2025
Publication Date: 1/30/2025
Citation: Dang, Y., Green, M.A., Wang, X., Duan, J.J. 2025. Comparative responses of two congeneric larval parasitoids of emerald ash borer to ambient temperatures: implications for biocontrol introduction. Biological Control. 202. Article 105718. https://doi.org/10.1016/j.biocontrol.2025.105718.
DOI: https://doi.org/10.1016/j.biocontrol.2025.105718

Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest in the United States and Canada. Two closely related parasitic wasps (Spathius agrili and Spathius galinae) were introduced to the United States of America to help control EAB between 2007 and 2015. To develop effective release strategies of these wasps across different regions of the United States, we compared their developmental responses to a range of constant temperatures from 17.2 to 32.8 ', which represent typical temperature during the spring, summer and fall in many EAB-invaded regions in the United States. Our findings suggest that S. agrili do better to control EAB in warmer climates than S. galinae, and could be effective as a biocontrol agent in the southern U.S., whereas S. galinae is better suited to be released in the northern U.S.

Technical Abstract: Understanding how climate influences the establishment of introduced species is critical to classical biological control programs against forest pests. Even closely related species with similar life histories may establish and perform differently in new environments due to inheritably different responses to ambient temperature. Here we compared the host attack rate and immature development of two congeneric larval parasitoids of emerald ash borer (EAB) Agrilus planipennis Fairmaire, Spathius agrili Yang and S. galinae Belokobylskij and Strazenac, under a range of temperatures from 17.2 to 32.8 '. We found significant differences between the two parasitoids in host attack rates and progeny development. Spathius agrili could parasitize EAB larvae across the temperature range of 17.2 ' to 32.8 ' and caused the highest parasitism rate (~90.0%) at 28.9 '. In contrast, S. galinae did not attack any host larvae at 32.8 ' and caused the highest parasitism rate (~92%) at 25 '. From 21.1 ' to 28.9 ', S. agrili emerged on average nine days earlier that S. galinae and had a higher low-temperature threshold for development, requiring fewer degree days for complete development to adults. Both species arrested their development as mature (5th) instars inside their cocoons at 17.2 ', suggesting facultative diapause that may be induced by exposure to cool temperatures. These findings suggest that S. agrili may perform better in warmer climates than S. galinae and could be an effective biocontrol agent in the southern U.S., whereas S. galinae is better suited to be released in the northern U.S.