The fungi and bacteria associated with three tree-killing beetles: from new species to complex communities.

Abstract

Fungi and bacteria can play critical roles in the life cycles of bark and woodboring beetles, influencing tree colonization and, in some cases, negatively impacting tree health. This dissertation investigates the microbial communities of two bark beetles and one woodboring beetle. The eastern larch beetle (Dendroctonus simplex) is a native bark beetle to North America that has undergone an unprecedented outbreak over the past two decades, impacting trees on over 90% of the tamarack (Larix laricina) forests within Minnesota. Prior to this work, its gallery-associated fungal communities were poorly characterized. This study demonstrated that Grosmannia americana is highly associated with the eastern larch beetle galleries in Minnesota. Additionally, four new species of Ophiostomatales are described and a new classification for one of the eastern larch beetle associates is proposed. The red turpentine beetle (Dendroctonus valens) is also a native bark beetle to North America and acts mostly as a secondary pest of pines throughout the continent, rarely killing healthy trees. A community-level analysis of the fungal and bacterial communities associated with the red turpentine beetle adults and their galleries found that red pine (Pinus resinosa) and white pine (P. strobus) host different microbial communities. Additionally, a rich diversity of Ophiostomatales were isolated from red turpentine beetle environments in the Great Lakes region, where Leptographium terebrantis was the most isolated species. Finally, the emerald ash borer (Agrilus planipennis), an invasive woodboring beetle in North America, has caused extensive damage to ash (Fraxinus spp.) over the past two decades, threatening an entire genus of trees. This dissertation studies how the fungal and bacterial communities in ash trees change during an emerald ash borer infestation. As the emerald ash borer attack progressed, fungal species richness declined. Additionally, most of the microbial species found in the emerald ash borer galleries were not detected in the phloem of trees without the emerald ash borer, however, the abundances of the latent microorganisms were higher in the galleries than the non-latent microorganisms. Overall, the findings in this dissertation contribute to the understanding of the fungi and bacteria associated with tree-killing beetles both on a microbial community-level and individual fungal species-level.