Do mites phoretic on elm bark beetles contribute to the transmission of Dutch elm disease? (original) (raw)

Abstract

Dutch elm disease (DED) is a destructive vascular wilt disease of elm (Ulmus) trees caused by the introduced Ascomycete fungus Ophiostoma novo-ulmi. In Europe, this DED pathogen is transmitted by elm bark beetles in the genus Scolytus. These insects carry phoretic mites to new, suitable habitats. The aim of this study was to record and quantify conidia and ascospores of O. novo-ulmi on phoretic mites on the three elm bark beetle species Scolytus multistriatus, Scolytus pygmaeus, and Scolytus scolytus. Spores of O. novo-ulmi were found on four of the ten mite species phoretic on Scolytus spp. These included Elattoma fraxini, Proctolaelaps scolyti, Pseudotarsonemoides eccoptogasteri, and Tarsonemus crassus. All four species had spores attached externally to their body surfaces. However, T. crassus carried most spores within its sporothecae, two paired pocket-like structures adapted for fungal transmission. Individuals of Pr. scolyti also had O. novo-ulmi conidia and ascospores frequently in their digestive system, where they may remain viable. While E. fraxini and P. eccoptogasteri rarely had spores attached to their bodies, large portions of Pr. scolyti and T. crassus carried significant numbers of conidia and/or ascospores of O. novo-ulmi. P. scolyti and T. crassus, which likely are fungivores, may thus contribute to the transmission of O. novo-ulmi, by increasing the spore loads of individual Scolytus beetles during their maturation feeding on twigs of healthy elm trees, enhancing the chance for successful infection with the pathogen. Only S. scolytus, which is the most efficient vector of O. novo-ulmi in Europe, carried high numbers of Pr. scolyti and T. crassus, in contrast to S. multistriatus and S. pygmaeus, which are known as less efficient vectors. The high efficiency of S. scolytus in spreading Dutch elm disease may be partly due to its association with these two mites and the hyperphoretic spores of O. novo-ulmi they carry.

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Acknowledgments

We thank Clive M. Brasier, Evert E. Lindquist, Alex C. Mangini, Dale S. Starkey, Joan F. Webber, Tatiana Czeschlik, and three anonymous reviewers for comments on earlier versions of the manuscript. Alexandr A. Khaustov identified specimens of E. fraxini. Don A. Griffiths provided advice regarding the bioassays of the gut contents of Proctolaelaps scolyti. Alexander Thuroczy (Dr. Karl Draskovich'sche Forstverwaltung Güssing, Austria) helped to collect the elm stem sections in Austria and Petr Zabrabsky organized the elm material infested by S. scolytus in the Czech Republic. Heino Konrad was supported by a grant from the foundation “120 Jahre Universität für Bodenkultur”, founded by Rupert Hatschek. The experiments and data collected here comply with the laws of Austria and Czech Republic.

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  1. Heino Konrad
    Present address: Unit of Gene Conservation and Nurseries, Department of Genetics, Federal Research and Training Centre for Forests, Natural Hazards and Landscape (BFW), Hauptstraße 7, 1140, Vienna, Austria

Authors and Affiliations

  1. Southern Research Station, USDA Forest Service, 2500 Shreveport Highway, Pineville, LA, 71360, USA
    John C. Moser & Stacy R. Blomquist
  2. Institute of Forest Entomology, Forest Pathology, and Forest Protection (IFFF), Department of Forest and Soil Sciences, University of Natural Resources and Applied Life Sciences, Vienna (BOKU), Hasenauerstraße 38, 1190, Vienna, Austria
    Heino Konrad & Thomas Kirisits

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  1. John C. Moser
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  2. Heino Konrad
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  3. Stacy R. Blomquist
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  4. Thomas Kirisits
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Correspondence toJohn C. Moser.

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Moser, J.C., Konrad, H., Blomquist, S.R. et al. Do mites phoretic on elm bark beetles contribute to the transmission of Dutch elm disease?.Naturwissenschaften 97, 219–227 (2010). https://doi.org/10.1007/s00114-009-0630-x

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