Date of Award

12-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Entomology

Advisor

Culin, Joseph D

Committee Member

Jeffers , Steven N

Committee Member

Bellinger , Robert G

Committee Member

Shelburne , Victor B

Committee Member

Hedden , Roy L

Abstract

The purpose of this study was to examine the development rates of hemlock woolly adelgid (HWA) infestations on sites containing primarily eastern hemlock, sites that contained predominantly Carolina hemlock, and sites where the two species occurred together, and to quantify the relationship between HWA density and canopy thinning in hemlocks. The study was conducted at 11 sites in DuPont State Forest near Brevard, NC, one site in nearby Caesar's Head State Park, Cleveland, SC, and one site near Whiteside Mountain, near Highlands, NC. In the second year of the study, one of the three Carolina hemlock sites was treated with insecticidal soap by DuPont State Forest employees and another Carolina hemlock site had all site flagging removed by unknown persons, leaving only one site for analyses. At all sites consisting mainly of either eastern or Carolina hemlock, five trees were monitored, while in all mixed species sites five trees of each species were monitored. HWA density was recorded on two 2 cm segments chosen at random on each of four branches per tree, with one branch selected from each cardinal direction. These data were used to calculate mean HWA densities per tree and per site. Density measurements were recorded monthly from March through June 2007 and 2008. Canopy density was measured by recording the amount of light reaching the forest floor beneath each tree in the study as umol m­² s­¹. One average light penetration reading was recorded annually for each tree in the study in 2006, 2007, and 2008. There were no significant differences in the average number of HWA found on either eastern hemlock or Carolina hemlock at any site in either 2007 or 2008. The four site groupings used for analysis were eastern hemlocks in eastern hemlock sites, Carolina hemlocks in Carolina hemlock sites, and both species at mixed hemlock sites. Three out of four site groupings had significantly lower HWA densities in 2008 compared to 2007. Except for the predominantly eastern hemlock site in 2008, there were no significant differences in light penetration data for Carolina hemlock or eastern hemlock at any site from 2006 through 2008. HWA infestations were significantly lower in 2008 than 2007 in three out of four site groupings. From 2006 to 2008, light transmission was only significantly different on the sites consisting of eastern hemlock, with significantly higher light readings in 2008 than either 2006 or 2007. Based on the lack of significant differences in HWA density on eastern hemlock and Carolina hemlock and in the amount of light transmitted through the canopy, this study suggests that eastern hemlock and Carolina hemlock are equally vulnerable to HWA infestation.
Soil drench applications of imidacloprid and dinotefuran were compared to bark spray applications of imidacloprid and dinotefuran in a tank mix with the bark penetrating surfactant PENTRA-BARK® for control of HWA. Each treatment was applied to five trees on October 12, 2007. Branch samples were taken in October (before treatment), November 2007 (26 days post treatment), December 2007 (51 days post treatment), and May 2008 (176 days post treatment) to determine both HWA mortality and insecticide concentration within each tree. In November, there were no significant differences in mean HWA morality among treatments. However, in December and May both dinotefuran treatments had significantly higher HWA mortality than the control. There was no significant difference in HWA mortality between the soil drench and bark spray applications for either insecticide. Results of insecticide concentration analyses were inconsistent, possibly due to matrix effects, the binding of the active ingredient to other analytes in the sample, making recoveries difficult, or the sensitivity of the analytical method used. Imidacloprid concentrations in both application methods varied widely among post treatment dates, while dinotefuran was often undetected. The difficulties in recovering both compounds from hemlock foliage did not allow for a conclusive determination as to whether either insecticide was directly related to HWA mortality.

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Entomology Commons

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