Date of Award

2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Natural Resources

First Advisor

Wallin, Kimberly

Abstract

Eastern and Carolina hemlock in the eastern United States are experiencing high mortality due to the invasive non-native hemlock woolly adelgid (HWA). The most promising means of control of HWA is the importation of natural enemies from the native range of HWA for classical biological control. Prior to release, natural enemies must be tested for suitability as a control agent, including the ability to locate the target prey. Coleopteran predators, including Scymnus coniferarum and Laricobius osakensis are under consideration as a means of biological control of HWA. Laricobius nigrinus was released in hemlock forests in 2003. It was recently discovered to hybridize with the native Laricobius rubidus. Behavioral responses of these predators to HWA and host tree foliage were observed using a 4-chambered olfactometer, and genetic analysis was used to differentiate responses of L. nigrinus, L. rubidus, and hybrids. In the olfactometer, insects are allowed to amble about the arena and respond to volatile cues from each treatment. Host foliage with and without HWA was tested, as were various comparisons of eastern versus western foliage, host versus non-host foliage, and foliage containing HWA and a congeneric feeding beetle. Olfactometer bioassays demonstrated that foliage from hosts where prey is commonly found is preferable to foliage where prey is seldom found, and that the presence of HWA-induced volatile cues is the strongest driver of behavior, and trumps the presence of a competitor. There is evidence in the study that supports the reliability-detectability phenomenon common in parasitoid biological control agents. Hybrid individuals were found to behave similarly to released L. nigrinus, although in some cases intermediate behavioral traits were evident, with respect to the parental species. This study and others support the continued need for strict testing of potential biological control agents prior to release, as well as a strong impetus for the inclusion and implementation of genetic analysis as a standard component of agent evaluation.

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