Masters Theses

Date of Award

5-2015

Degree Type

Thesis

Degree Name

Master of Science

Major

Forestry

Major Professor

Adam Taylor

Committee Members

Albert Mayfield III, Scott Myers, William Klingeman III

Abstract

Nonnative, invasive forest insect pests are a significant threat to the health of global forest resources. Thousand cankers disease, a recently described disease threatening walnuts, is the result of an invasive insect-pathogen complex in which the walnut twig beetle (Pityophthorus juglandis Blackman) is a vector to the associated fungal pathogen, Geosmithia morbida. Both are native to the southwestern U.S. into northern Mexico, however, have been found well beyond their historic range, and now threaten black walnut (Juglans nigra) in the eastern U.S. Beetles have likely been spread via the transport of infested walnut logs.

The goal of this project was to identify potential pathways by assessing P. juglandis colonization of J. nigra logs and seedlings, and to identify treatments to prevent colonization in logs. Beetle colonization of logs and lumber treated by phytosanitation measures was tested. When exposed to high colonization pressures and baited with a pheromone lure, beetles attacked steam heated, methyl bromide fumigated, and kiln-dried samples. Colonization in a reduced pressure exposure scenario was inconclusive.

Azadirachtin, borate, and permethrin were tested as a means of preventing P. juglandis colonization of black walnut logs. Beetle survival rates over a 120 hour exposure period, and colonization activity was compared. Permethrin was the only insecticide to kill all beetles and to prevent any attacks. A 30% concentration of borate showed some control, reducing survival rate compared to control levels, however, beetles successfully attacked the material, and its use as a control method is questionable. Azadirachtin was not effective in the doses tested.

Finally, P. juglandis colonization of J. nigra nursery stock seedlings was tested. Seedlings were exposed to beetles in no-choice and choice assays. For no-choice assays, beetles were caged directly onto the stems. In choice assays, seedlings were placed near infested logs, presenting the seedlings to beetles emerging from the infested material. Beetles attacked stems in all diameter size classes tested (0.5 – 2.0 cm), however, showed a preference for larger diameter trees. No attacks were observed in the choice assays and may have been confounded by the method used to introduce beetles to seedlings.

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