Date of Award

2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Plant and Soil Science

Abstract

The eastern hemlock is a late-successional conifer species that is valued for its ecological functions, recreational importance, aesthetic beauty, and economic value. The hemlock woolly adelgid (HWA, Adelges tsugae Annand, Homoptera: Adelgidae) is an invasive aphid-like insect from Asia that is causing serious damage to the eastern and Carolina hemlock. HWA was first introduced to the Eastern United States to Virginia in the 1950’s and has since moved along the east coast from Georgia to Maine. It can kill a healthy tree in three to seven years depending on many environmental factors. Native predators have not been successful in reducing damage to hemlock trees or limiting the spread of HWA. Chemical, cultural, and biological control efforts have been implemented in states with high populations of HWA. Chemical applications are costly and current formulations are difficult to apply in large stands and in forested areas. Salvage cutting is a method to control the spread of adelgid and recover some economic value of the wood. Predatory beetles native to Asia, where HWA is present but not a severe problem, have been researched, reared, and released into infested stands in the Eastern United States. Their success for management of HWA has been difficult to ascertain. The entomopathogenic fungus Lecanicillium muscarium ((Petch) Zares & Gams) is another biological control agent with potential to manage and suppress adelgid populations. L. muscarium (Mycotal™ technical powder, Koppert Biological Systems) plus the nutritive base sweet whey, may promote conidia production without contact with a host and this means of increasing conidia is called a whey-based fungal microfactory. The whey would act as a nutritive substrate for fungi sprayed into hemlock forests. Formulation droplets deposited on hemlock needles should support fungal growth and serve as tiny factories for conidia production. Microfactory production was characterized in different combinations of sweet whey (0, 5, 10, and 15%) and conidia concentration (1 x 106, 1 x 107, and 1 x 108 conidia/ml) applied to lids of Petri dishes. A dramatic 42- and 29-fold increase in conidia production occurred with the addition of 10% sweet whey to 1 x 106 and 1 x 107 conidia/ml, respectively. Increasing whey concentration increased the number of conidia that were recovered. Conidia production was also obtained on hemlock foliage, with similar trends in influence of conidia and whey concentration. The hemlock branches also contained HWA and their mortality was evaluated. Adelgid mortality was highest in formulations containing sweet whey, but whey had an independent effect on mortality. Several antimicrobials were evaluated for compatibility with L. muscarium in the microfactory formulation. Nisin did not inhibit conidia production. The addition of antimicrobials to the whey-based formulations may limit the competition between the fungus and other microbes present in the spray tank and on foliage. Whey-based fungal microfactory technology is intended to facilitate multiplication of fungi in the natural environment. Transferring a portion of fungal massproduction into the treatment environment could reduce application costs and increase the feasibility of using fungi for biological control of HWA and other pest species.

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