Year of Award

2007

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Forestry

Department or School/College

College of Forestry and Conservation

Committee Co-chair

Diana Six, Carl Fiedler

Commitee Members

Barbara Bentz, Doug Emlen, John Maron, Kelsey Milner

Keywords

bark beetles, Dendroctonus ponderosae, mountain pine beetle, mutualism, ophiostomatoid fungi, symbiosis

Abstract

I investigated interactions between the mountain pine beetle (Dendroctonus ponderosae) and its two main ophiostomatoid fungal associates,Grosmannia clavigera and Ophiostoma montium, as well as interactions between the two fungi. The main research questions were: What drives bark beetle fungal interactions? What is the nature of the interaction between the two species of fungi? I tested the hypothesis that the fungi provide nutritional benefits to the bark beetles. Evidence suggests a nutritional role of fungi in the diet of bark beetles because beetles emerging from attacked trees carrying G. clavigera were larger than beetles carrying O. montium, which in turn were larger than beetles without either fungus. Larval choice feeding experiments indicate that the two fungi may actually provide complimentary benefits. To address the second question, I tested for competition between the two fungi on artificial media. Growth of each species slowed when it encountered media occupied by the other species, indicating competition; however, both species eventually invaded media occupied by the other species. Although G. clavigera colonized unoccupied media the fastest, O. montium was more effective in colonizing media occupied by G. clavigera when their relative growth rates were considered. In another study, the relative abundances of the two fungi were sampled in beetle-attacked trees in the field over the one year life cycle of the insect. I found no evidence of interference competition, but exploitation competition was prevalent after a year when the fungi co-occurred in the phloem. Finally, I examined whether the two fungi are differentially transported in the mycangia and on the exoskeleton of the beetle using scanning electron microscopy and isolating fungi from the mycangia and elytra. I found no evidence of differential transport of G. clavigera or O. montium in the mycangia and on the exoskeleton from isolation data. There was also no evidence that one fungus was more likely to be transported on the exoskeleton than the other species using electron microscopy. The fungi appear to exist in the mycangium in an altered, yeast or yeast-like state rather than as conidia.

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© Copyright 2007 Katherine Patricia Bleiker