Host range expansion may provide enemy free space for the highly invasive emerald ash borer

Abstract

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an aggressive invader from Asia that has killed millions of trees in North America, causing substantial ecosystem effects and economic losses. All North American ash, Fraxinus spp., are thought to be susceptible, but recently emerald ash borer has been documented developing in a novel host, white fringetree, Chionanthus virginicus. We evaluated larval performance in two common ash species and white fringetree by infesting bolts with emerald ash borer eggs. In addition we evaluated cambial nitrogen, carbon, carbon:nitrogen, stem density, and response to artificial wounding, to determine which host plant characteristics most influence larval development. We also conducted choice and no choice assays using the classical biological control agent, Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), to assess its ability to locate larval emerald ash borer in the different host plants. We found significantly lower survival rates of emerald ash borer larvae in white fringetree compared to white ash, F. americana. Larval phloem consumption and larval growth were lower in fringetree than in either white or blue ash, F. quadrangulata. Carbon content and density were greater in fringetree than in either ash species. Response to wounding, measured by callus tissue formation, was greatest in white ash. In choice assays, T. planipennisi only parasitized emerald ash borer larvae in ash bolts, and in no-choice tests failed to parasitize larvae in fringetree. Our findings corroborate studies showing that fringetree is a suitable host for emerald ash borer larvae. Failure of T. planipennisi to parasitize larvae within fringetree has implications for the efficacy of this classical biological control agent in regulating emerald ash borer populations. Coupled with the use of white fringetree as a reservoir host, the enemy free space provided to emerald ash borer through use of this alternate host may have significant repercussions for emerald ash borer invasion dynamics.

Considerations regarding species distribution models for forest insects

“…What if the insect is a specialist? For instance, the emerald ash borer (Agrilus planipennis Fairmaire) is essentially limited to hosts in the ash (Fraxinus) genus (but see Cipollini & Peterson, 2018;Olson & Rieske, 2019). A less specialized insect is the Asian longhorned beetle (Anaplophora glabripennis (Motschulsky)), for which the preferred hosts include maples (Acer), willows (Salix), and elms (Ulmus), while birch (Betula) and sycamore (Platanus) species are also common hosts (Haack et al, 2010).…”

Confocal microscopy provides visual evidence and confirms the feasibility of dsRNA delivery to emerald ash borer through plant tissues

“…Ingestion of dsRNA-treated ash tissue by developing neonate larvae (Table 1c) was evaluated using the same greenhouse-grown tropical ash described above. Branches were artificially infested with laboratory-reared EAB eggs (Olson and Rieske 2019) prior to branch excision. Briefly, pieces of coffee filter (Kroger, Cincinnati OH) with laboratoryreared EAB eggs laid on them were attached to branches and secured using 1.5-cm-wide strips of parafilm (Bernis NA, Neenah, WI).…”

“…There were five branches per treatment (labeled dsGFP and water), each one artificially infested with six EAB eggs. After 8 days the treated branches were carefully debarked using a sharp knife, and EAB egg hatch, larval development, and phloem consumption were evaluated (Olson and Rieske 2019); confocal microscopy was used to evaluate labeled dsRNA uptake.…”

Lessons from the Frontline: Exploring How Stakeholders May Respond to Emerald Ash Borer Management in Europe

“…The widescale loss of ash trees in the USA through EAB has created significant social and economic impacts with residents in urban and peri-urban neighborhoods having been particularly affected by EAB-induced ash mortality and the treatment or removal and replacement of large ash trees [6][7][8][9]. EAB has also been documented to have expanded its host range to species such as white fringe tree (Chionanthus virginicus) suggesting that it does not depend totally on ash to survive and could pose a serious risk to other important Oleaceae species in Europe [10,11]. As of January 2019, EAB had spread to 35 states in the USA and five provinces in Canada and killed or infested millions of ash trees [12].…”