Niche partitioning and coexistence of parasitoids of the same feeding guild introduced for biological control of an invasive forest pest

Authors: Duan, Jian; VAN DRIESCHE, ROGY - University Of Massachusetts, Amherst; Schmude, Jonathan; QUINN, NICOLE - University Of Massachusetts, Amherst; PETRICE, TOBY - Us Forest Service (FS); RUTLEDGE, CLAIRE - Connecticut Agricultural Experiment Station; POLAND, THERESE - Us Forest Service (FS); BAUER, LEAH - Us Forest Service (FS); ELKINTON, JOE - University Of Massachusetts, Amherst

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2021
Publication Date: 6/27/2021
Citation: Duan, J.J., Van Driesche, R., Schmude, J.M., Quinn, N.F., Petrice, T., Rutledge, C., Poland, T., Bauer, L.S., Elkinton, J. 2021. Niche partitioning and coexistence of parasitoids of the same feeding guild introduced for biological control of an invasive forest pest. Biological Control. 160. https://doi.org/10.1016/j.biocontrol.2021.104698.
DOI: https://doi.org/10.1016/j.biocontrol.2021.104698

Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest that has killed tens of millions of ash trees in the United States and Canada. Two parasitic wasps (Tetrastichus planipennisi and Spathius galinae) attacking EAB larvae have been introduced from Northeast Asia to the U.S. for biocontrol of the pest between 2007 and 2015. We evaluated their status following field releases in midwestern and northeastern hardwood forests and found that the two biocontrol agents have successfully established coexisting populations at all of the release sites in both regions. The parasitoid populations show large differences in presence, abundance, and EAB attack rates in ash trees of different size classes, with S. galinae more frequent in larger diameter and pole size trees and T. planipennisi dominating in saplings. This shows that the two introduced biocontrol agents complement one another in protecting ash trees of different size classes against EAB in North America.

Technical Abstract: 1. When multiple species of host-specific natural enemies from the same feeding guild are introduced either sequentially or simultaneously to an area against a target pest, strong interspecific competition is likely and may compromise biocontrol unless the agents can effectively partition available resources. 2. Here, we evaluate if two parasitoids (Spathius galinae and Tetrastichus planipennisi), introduced for biocontrol of the invasive emerald ash borer (EAB), Agrilus planipennis, in the United States have established niche-partitioning, co-existing populations following their sequential or simultaneous field releases to 12 hard-wood forests located in midwest and northeast regions. 3. Results show that the two recently introduced EAB larval parasitoids, S. galinae and T. planipennisi, have established niche-partitioning, co-existing populations in all release areas. The two parasitoid populations in these forests also show strong differentiation in presence, abundance, and/or host attack rates in ash trees of different size classes, with S. galinae parasitism being more frequent in larger diameter and pole size trees and T. planipennisi dominating in saplings. 4. Although host larval abundance decreases significantly with the height of a sampled tree or sapling because of the reduction in the tree phloem volume, the abundance of the parasitoid broods is not affected by the tree height, but strongly driven by the EAB larval abundance in the sampled section of their preferred tree-size classes. 5. These findings suggest that these two introduced specialist parasitoids, S. galinae and T. planipennisi, complement one another in protecting trees of different size classes against EAB, and thus both are needed in successful biocontrol of EAB in North America.