The role of emerging hosts in the North American emerald ash borer invasion: Implications for natural enemy-free space
The invasive emerald ash borer (EAB) has been inflicting catastrophic damage on North American ash resources for over two decades. In its native range, EAB is a secondary pest of Manchurian ash (Fraxinus mandshurica), attacking and killing stressed trees. In North America, EAB’s host range has expanded to include healthy trees of every Fraxinus species encountered, most recently Oregon ash (F. latifolia). Successful EAB development has also been reported on two non-ash hosts: white fringetree (Chionanthus virginicus) and European olive (Olea europaea). However, little is known about how EAB interacts with these novel hosts for development or how natural enemies respond to EAB developing on these novel host plant species. The objectives of this study were threefold: (a) to determine the ability of Oregon ash, white fringetree, and European olive to support complete EAB larval development, (b) to assess the responses of larval parasitoids to EAB developing in these hosts, and (c) to observe how these factors interact to determine EAB net population growth rates on novel hosts. We conducted laboratory and field infestations of Oregon ash, white fringetree, and European olive bolts and trees, comparing EAB larval size and survival on each species over time. We also assessed the responses of larval parasitoids to EAB developing on novel hosts in laboratory exposures and field infestations. We found that Oregon ash is a suitable host for EAB, with no difference in larval size, development, or net population growth rate when compared with EAB developing on green ash. We also found that larval parasitoids Spathius agrili, Spathius galinae, and Tetrastichus planipennisi can find and attack EAB developing in Oregon ash. In contrast, larvae developing on white fringetree and olive died earlier and were smaller than larvae developing on ash. Though there was no evidence of larval parasitism in these non-ash hosts, net population growth rates were close to 0 on both, indicating that EAB populations on these species are unlikely to be self-sustaining.
Biocontrol, Ecological fitting, Emerald ash borer, Invasive species, European olive, White fringetree
Networked Digital Library of Theses and Dissertations