Masters Theses

Date of Award

8-2007

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Paris L. Lambdin

Committee Members

Jerome Grant, Nathan Sanders, James Rhea, Nicole Labbé

Abstract

Hemlock woolly adelgid, Adelges tsugae Annand, is an exotic insect species dramatically reducing populations of eastern hemlock, Tsuga canadensis (L.) Carrieré, throughout the eastern United States. Systemic imidacloprid and horticultural oil are the two primary chemicals used to control infestations of the hemlock woolly adelgid. However, the effect of application timing (fall versus spring) and method on the translocation of imidacloprid throughout the canopy in addition to the quantity of imidacloprid translocated is unknown. Also, the potential effect of both imidacloprid and horticultural oil on non-target canopy insects is unknown. A study was initiated to determine the effect of application timing (fall versus spring) for three imidacloprid application methods (soil drench, soil injection, and tree injection) on the translocation of imidacloprid and concentration levels accumulated in eastern hemlock sap and twig and needle samples, assess the effect of these treatments and horticultural oil on the overall species richness and abundance, guild species richness and abundance, and specific species of non-target phytophagous and transient canopy insects.

Eastern hemlocks (n = 30) were selected at Indian Boundary in Cherokee National Forest located in southeast Tennessee on 5 November 2005. This test was arranged in a split plot 2 x 5 factorial complete randomized block design with three replications. Three blocks were established. Each block contained ten trees, arranged in five tree pairs, with one tree in the pair treated in the fall (29-30 November 2005) and the other during the spring (16 April 2006). Five treatments were made; horticultural oil, imidacloprid soil drench, imidacloprid soil injection, imidacloprid tree injection, and the control (no treatment). Enzyme-linked immunosorbant assays were used to determine imidacloprid concentration in sap and combined twig and needle concentrations collected from hemlock branches at three strata (bottom, middle, and top) of the hemlock canopy collected every three months post-treatment. To determine effect on phytophagous and transient canopy insects, monthly sampling consisting of malaise traps, beat-sheets, direct observation/trunk vacuuming/handpicking, and branch pruning was conducted from 16 March 2006 - 18 April 2007.

Concentration levels progressively decline from the bottom strata to the top strata of the canopy. This trend was consistent in all chemically treated trees. Tree injections provided the lowest concentration and the most non-uniform distribution of imidacloprid throughout the canopy. Soil drench consistently provided the highest insecticide concentration within the tree across all strata.

Species richness and abundance were significantly effected by one or more application methods when compared to the control trees; however, the timing of the applications (fall versus spring) had no significant effect on the insect species. The detritivore and phytophaga guilds were effected by one or more chemical applications. Species richness was significantly lower across all guilds and differed significantly from those species on the control trees. Some 35 insect species were found to be directly effected by these chemical treatments. Of the 35 species, 27 feed directly on eastern hemlock, and as such, ingest the chemical. Eight of the species were psocopterans that feed on decaying organic material (detritivore). The soil drench had the greatest effect on species richness and abundance and guild richness and abundance among non-target phytophagous and transient canopy insects, followed by soil injection, while horticultural oil and tree injections had minimal effect. This data provides more flexibility in the timing and method of application used to have a minimal effect on non-target phytophagous and transient canopy insects.

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