Assessment of Alternative Candidate Subcortical Insect Vectors From
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Environmental Entomology, 48(4), 2019, 882–893 doi: 10.1093/ee/nvz064 Advance Access Publication Date: 30 May 2019 Pest Management Research Assessment of Alternative Candidate Subcortical Insect Vectors From Walnut Crowns in Habitats Quarantined for Thousand Cankers Disease Downloaded from https://academic.oup.com/ee/article-abstract/48/4/882/5506619 by Purdue University Libraries ADMN user on 19 May 2020 Karandeep Chahal,1,2 Romina Gazis,3 William Klingeman,4,5 Denita Hadziabdic,1 Paris Lambdin,1 Jerome Grant,1 and Mark Windham1 1Department of Entomology and Plant Pathology, University of Tennessee, 370 Plant Biotechnology Building, Knoxville, TN 37996, 2Current address: Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI 48824, 3Department of Plant Pathology, Tropical Research & Education Center, University of Florida, Homestead, FL 33031, 4Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Dr., 252 Ellington Plant Sciences Building, Knoxville, TN 37996, and 5Corresponding author, e-mail: [email protected] Subject Editor: David Onstad Received 7 February 2019; Editorial decision 2 May 2019 Abstract Thousand cankers disease (TCD) results from the combined activity of the fungal pathogen, Geosmithia morbida Kolařík, Freeland, Utley, and Tisserat and its principle vector, Pityophthorus juglandis (Blackman) (Coleoptera: Curculionidae: Scolytinae) in Juglans L. spp. and Pterocarya Kunth spp. host plants. TCD has been reported from the eastern and western United States. To evaluate potential for other beetle species to vector the fungus in east Tennessee, specimens were collected using ethanol-baited traps that were suspended beneath crowns of TCD-symptomatic trees. Associations of G. morbida with insect species collected in traps were assessed in an unsuccessful, preliminary culture-based fungal assay, and then with a molecular-based detection method. For culture-based assays, rinsate from washed, individual insects was plated on nutrient media and growing colonies were subcultured to obtain axenic G. morbida cultures for identification. For the molecular-based method,G. morbida presence was detected by amplifying the previously developed, species-specific microsatellite locus GS004. Capillary electrophoresis was used to detect the amplified amplicons and representative reactions were validated using Sanger sequencing. Eleven beetle species were found to carry G. morbida, including Cnestus mutilatus (Blandford), Dryoxylon onoharaensum (Murayama), Hylocurus rudis (LeConte), Monarthrum fasciatum (Say), Monarthrum mali (Fitch), Xyleborinus saxesenii (Ratzeburg), Xylosandrus crassiusculus (Motschulsky), Xylosandrus germanus (Blandford) (all Coleoptera: Curculionidae: Scolytinae), Stenomimus pallidus (Boheman) (Coleoptera: Curculionidae: Cossoninae), Oxoplatypus quadridentatus (Olivier) (Coleoptera: Curculionidae: Platypodinae), and Xylops basilaris (Say) (Coleoptera: Bostrichidae). These findings raise concerns that alternative subcortical insect species that already occur within quarantined habitats can sustain incidence of introduced G. morbida and contribute to spread within the native range of black walnut, Juglans nigra L., in the eastern United States. Key words: subcortical insect, novel fungus-beetle association, Geosmithia morbida, pathogen vector, Pityophthorus juglandis Thousand cankers disease (TCD) has been considered as an emerg- of epicormic shoots (Tisserat et al. 2009). Internal symptoms include ing threat to health of walnut (Juglans L.) and wingnut (Pterocarya numerous small cankers, and vertical and horizontal galleries pro- Kunth) tree species (Utley et al. 2009, Hishinuma et al. 2016). TCD duced by walnut twig beetle in the inner bark/phloem (Kolařík et al. is a complex that involves a fungal pathogen, Geosmithia morbida 2011, Tisserat et al. 2011). The many cankers can coalesce, creating Kolařík, Freeland, Utley, and Tisserat (Ascomycota: Hypocreales: large necrotic areas that girdle the tree (Tisserat et al. 2009). All Bionectriaceae), an insect vector, walnut twig beetle, Pityophthorus examined Juglans spp. have demonstrated susceptibility to TCD; juglandis (Blackman) (Coleoptera: Curculionidae: Scolytinae), and however, black walnut (Juglans nigra L.) is the most susceptible host Juglans spp. and Pterocarya spp. host plants. External symptoms to the pathogen (Utley et al. 2013). of TCD include wilting, foliage chlorosis of the upper crown (flag- In the last two decades, TCD has resulted in severe mortality and ging), crown thinning, and branch dieback followed by emergence crown dieback of Juglans spp. in the western United States (Seybold © The Author(s) 2019. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: [email protected]. 882 Environmental Entomology, 2019, Vol. 48, No. 4 883 et al. 2016). Juglans nigra has an estimated value for standing timber supported by population genetic studies conducted on wide-scale in the United States that exceeds $568 billion (Newton and Fowler sampling across the United States and Italian populations of walnut 2009). The tree is one of the most economically valuable North twig beetle (Hadziabdic et al. 2014, Zerillo et al. 2014, Rugman- American hardwood species and has many uses including furniture, Jones et al 2015, Montecchio et al. 2016). veneer, cabinets, interior architectural woodwork, flooring, and gun- Geosmithia morbida, and walnut twig beetle are native to stocks (Manning 1978, Grant et al. 2011). In addition to the annual Southwestern United States, where they are associated with J. major market consumption of walnut wood in the United States, in 2017, Torr.; a walnut species that has been shown to have a higher toler- United States exported walnut lumber to more than 67 countries ance to the beetle and fungal damage (Utley et al. 2013). Subsequent and walnut logs to more than 49 countries that were valued at $258 range expansion and increase in disease severity can be explained by million, and $163 million, respectively (USDA-FAS 2018). a switch of the pathogen to a naïve host and habitat (Tisserat et al. Downloaded from https://academic.oup.com/ee/article-abstract/48/4/882/5506619 by Purdue University Libraries ADMN user on 19 May 2020 In Knoxville, Tennessee in 2010, TCD was detected within the 2011). Although not yet demonstrated in TCD, successful vector native range of J. nigra (Daniels et al. 2016), and this discovery pre- switching in other important pathosystems in the United States have sents a serious threat to J. nigra within urban and forest settings demonstrated negative consequences for native forested ecosystems across the distribution of susceptible Juglans spp. (Grant et al. (Wingfield et al. 2010, Saucedo-Carabez et al. 2018). Consequently, 2011). Subsequent TCD detections in the eastern United States emergence of novel beetle associations occurring within a compro- are now reported from Indiana, Maryland, North Carolina, Ohio, mised habitat presents practical concerns about the role of other sub- Pennsylvania, and Virginia (Hansen et al. 2011, Fisher et al. 2013, cortical insect species that are associated with walnut in spreading Seybold et al. 2013, Hadziabdic et al. 2014, Daniels et al. 2016), as and sustaining TCD within the native range of J. nigra (e.g., Juzwik well as Italy (Montecchio and Faccoli 2014, Moricca et al. 2019). et al. 2015, Klingeman et al. 2017). Fungi within the genus Geosmithia Pitt comprise genetically Walnut twig beetle is considered the primary vector of G. mor- and ecologically diverse lineages with mainly asexual mode of bida in the United States, yet other scolytid beetles associated with reproduction. This genus has a global distribution, having been J. nigra trees in the western United States have been suspected as reported from North and South America, Europe, Asia, and potential alternative vectors of the fungus (Newton and Fowler Australia (Pitt 1979, Kolařík et al. 2008, Lin et al. 2016, Kolařík 2009). Using morphological and molecular methods, G. morbida et al. 2017). Geosmithia spp. occupy diverse ecological niches was recovered from the weevil Stenomimus pallidus (Boheman) with species that are thermophilic, mesophilic, or thermotolerant (Coleoptera: Curculionidae: Cossinae) collected in Brown County, (Kolařík et al. 2004). Although most Geosmithia spp. are sapro- Indiana (Juzwik et al. 2015), and P. juglandis was detected both in phytic, some species can act as weak pathogens (Schuelke et al. a trap and from logs at a sawmill in Franklin County, Indiana in 2017). Some Geosmithia spp., including G. morbida, have been 2014 (Indiana Department of Natural Resources 2015). Walnut twig characterized as having strong associations with specific phloeoph- beetle has not been recovered in Indiana since that time (Thousand agous bark beetle species, or interactions that are limited within Cankers Disease Research and Management Operational Meeting narrow taxonomic groups, that serve a critical function in vector- 2017). In Ohio, the fungus has been recovered from S. pallidus and ing these fungal species among healthy host trees (Kolařík et al. two ambrosia beetle species, Xylosandrus crassiusculus Motschulsky 2007, Huang et al. 2017). Other Geosmithia spp. show varying and Xyleborinus saxesenii Ratzeburg (Coleoptera: Curculionidae: levels of specificity to their beetle vectors and tree hosts that range Scolytinae) (Juzwik et al. 2016). Association