Date of Graduation

2016

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Horticulture

Committee Chair

Matthew T Kasson

Committee Co-Chair

William L MacDonald

Committee Member

Daniel G Panaccione

Committee Member

Yong-Lak Park

Abstract

Hemlock woolly adelgid (HWA) is an exotic insect pest of eastern hemlock. The entomopathogen Lecanicillium muscarium, including the commercially available strain MycotalRTM, is a potential candidate for fungal biocontrol. There are many factors to consider when using a fungal biocontrol such as ecology and genetic variation of candidate strains and interactions with other fungi and life stages of the target insect pest. Efforts of this study focused on: 1) sampling for reservoirs for L. muscarium and other Lecanicillium spp., 2) elucidating interactions between Lecanicillium and other fungi present in hemlock tissues and 3) characterizing genetic diversity of Lecanicillium and subsequent entomopathogenicity against HWA. Six Lecanicillium isolates were recovered out of 2,954 total fungal colonies isolated across all substrates, resulting in <1% incidence. Sampling of Mycotal RTM-treated hemlock stands failed to recover any Lecanicillium isolates, which suggests that Lecanicillium does not persist in these environments. To help explain low incidence of Lecanicillium recovery, common fungal community members recovered from these same hemlock tissues were co-plated with Lecanicillium to evaluate inhibitory effects. These frequently recovered fungi included Colletotrichum, Epicoccum, Pestalotiopsis, Rhizosphaera and an undescribed Leotiomycete. The Leotiomycete was shown to have inhibitory effects on several species of Lecanicillium. Since the Leotiomycete fungus is present 17% of the time on average, this could be a significant factor influencing the persistence of Lecanicillium in the environment. To further understand relationships among Lecanicillium, multi-gene phylogenetic analyses were conducted. Six separate phylogenetic analyses, with data partitioned by individual genes produced some complementary results and supported the monophyly of Lecanicillium sensu strictu and close relationships among L. muscarium and L. longisporum as well as uncovered novel linages of Lecanicillium. The phylogenetic trees informed selection of a diverse set of isolates used in entomopathogenicity testing. All isolates used were found to be pathogenic against HWA but virulence among fungal species and isolates varied. Mycotal RTM utilizes a virulent strain for an inundative augmentative approach to bolster naturally low population of Lecanicillium present in hemlock stands. However, its low infection rate on egg masses (33%) could indicate that other Lecanicillium isolates used in this study, especially North American strains, might be a better candidate for widespread application against HWA in the eastern United States.

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