Masters Theses

Date of Award

12-2006

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Paris Lambdin

Committee Members

Jerome Grant, Kevin Moulton, Rusty Rhea

Abstract

A project was initiated in September 2004 to determine the indigenous predators of Fiorinia externa Ferris, the elongate hemlock scale (EHS), on eastern hemlock and their impact on the pest populations. Branch samples were taken monthly from four sites (two forest and two urban) in eastern Tennessee and western North Carolina to assess predator damage from October 2004 to April 2006. Predators of this exotic pest were collected from beat sheet samples from September 2004 to May 2006. Laboratory tests were conducted from field-collected predators to assess food consumption, feeding behavior, and intraguild competition among predators of EHS. From field samples, the average predator damage was 8.28% (range 4.72 to 9.84%) for the four sites, and predator damage was found throughout the year. Six predaceous species (Chilocorus stigma, Harmonia axyridis, Rhyzobius lophanthae, Scymnillus horni, Scymnus loweii, and Conwentzia pineticola) were documented to feed on EHS. There were 346 total adult predators, one pupa, and 157 larvae collected from September 2004 through May 2006. Rhyzobius lophanthae was the only predator collected throughout the year. The highest numbers of specimens collected were from the urban sites. Chilocorus stigma, R. lophanthae, and S. horni had the highest EHS consumption rates. From the functional tests, S. horni, R. lophanthae, and C. stigma exhibited different searching patterns for recognizing EHS as prey. Chilocorus stigma had the shortest prey recognition times, while R. lophanthae had the longest prey recognition times. Scymnus loweii did not feed during the functional tests. When four of the predators were tested in different combinations, all four exhibited aggressive tendencies, and this territorial behavior could cause feeding disruption. Rhyzobius lophanthae and S. horni consumed fewer Adelges tsugae females or immatures compared to EHS and were more prey specific. In fecundity tests, R. lophanthae most commonly laid eggs singly on a branch, needles, side of Petri dish, or filter paper than in clusters. It also laid eggs near or under EHS exuviae. Based on consumption and seasonal abundance, R. lophanthae, C. stigma, and S. horni should be further evaluated for use as biological control agents to complement the parasitoid, Encarsia citrina. (348 words)

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