Multipartite symbioses among fungi, mites, nematodes, and the spruce beetle, Dendroctonus rufipennis

The spruce beetle, Dendroctonus rufipennis, is an eruptive forest pest of significant economic and ecological importance. D. rufipennis has symbiotic associations with a number of microorganisms, especially the ophiostomatoid fungus Leptographium abietinum. The nature of this interaction is only partially understood. Additionally, mite and nematode associates can mediate bark beetle-fungal interactions, but this has not yet been studied for spruce beetles. In this study, we found eight mite species associated with spruce beetles: Tarsonemus ips, T. endophloeus, Histiogaster arborsignis, Dendrolaelaps quadrisetus, Proctolaelaps hytricoides, Trichouropoda alascae, T. n. sp. nr dalarenaensis, and Urobovella n. sp 767. The most prevalent species was H. arborsignis. In addition, 75% of beetles examined carried nematodes, with six species represented. These included a new species of Parasitorhabditis, Ektaphelenchus obtusus, Bursaphelenchus n. sp. 727, Aphelenchoides n. sp., Panagrolaimus sp., and Mykoletzkya ruminis. H. arborsignis showed strong feeding and oviposition preferences for L. abietinum among four fungal species tested in laboratory assays. Information on our attempts to culture the various nematode species collected from D. rufipennis is also provided. Bursaphelenchus were cultured from D. rufipennis nematangia plated on agar containing L. abietinum but not sterile agar. Thus, L. abietinum plays an important role in these gallery communities, affecting the tree-killing bark beetle, its phoretic mites, and nematodes. These data add to our understanding of bark beetle-microorganism interactions.