Date of Graduation
Davis College of Agriculture, Natural Resources and Design
In a globalized world, wood products are constantly being shipped from one location to another, along with tiny hitchhikers in the form of insects and microorganisms. Euwallacea validus is a fungus-farming ambrosia beetle native to East Asia that likely made its way to the United States in wood packaging materials in the latter half of the twentieth century. E. validus cultivates two fungal symbionts in the U.S., an unnamed Fusarium sp. (AF-4) and Raffaelea subfusca. Fusarium symbionts of Euwallacea ambrosia beetles as well as Raffaelea symbionts of closely related ambrosia beetles have incited widespread disease on more than one-hundred hosts worldwide. To resolve host range of Fusarium and Raffaelea symbionts from E. validus, inoculation studies, which mimicked natural infestation by creating numerous beetle-size holes along single stems, were conducted on twelve tree species native to the eastern United States known to be natural hosts for this beetle species. Four months post-inoculation, trees were destructively sampled to examine and measure symptoms associated with inoculation. Results of this study showed significant differences in canker incidence and mean streaking associated with inoculation sites, although neither Fusarium sp. AF-4 nor Raffealea symbionts caused significant disease on any host tested and do not appear to pose serious risks to the known hosts within the invaded range of this beetle. Nonetheless several other Euwallacea-Fusarium consortia have been introduced into the U.S. recently which do pose serious risks to avocado production and forest health. PCR multiplexes were recently developed to discriminate closely related AFC symbionts present in the U.S. to monitor their spread and have opened the door for widespread molecular surveillance. This includes testing whether fusaria differ between the native / invaded ranges of these beetles and if symbiont swapping is occurring between beetles whose ranges currently overlap in the U.S. Results of this study confirmed fidelity between certain Euwallacea sp. and their fungal partners such as E. validus and its symbiont, Fusarium sp. AF-4 in both South Korea and the U.S. with no evidence of additional AFC members despite uncovering other FSSC members within mycangial communities. No other Euwallacea spp. examined exhibited obvious fidelity between native and invaded ranges. Surprisingly, a number of known AFC lineages already existing in the U.S. were uncovered from the mycangia of other Euwallacea spp. within the geographic origin of beetles in East Asia. In addition to AFC members, other FSSC isolates were associated with galleries of all five Euwallacea spp. studied, indicating frequent interactions between symbiotic and asymbiotic FSSC members. These results uncovered widespread fungal infidelity among closely related Euwallacea beetles. Such novel beetle-fungus combinations could incite disease across a number of orchard, landscape, and forest trees.
Berger, Matthew C., "Interactions between Euwallacea Ambrosia Beetles, Their Fungal Symbionts and the Native Trees They Attack in the Eastern United States" (2017). Graduate Theses, Dissertations, and Problem Reports. 5186.