Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Richard A. Goyer

Abstract

Ecological relationships between the fruittree leafroller (FTLR), (Archips argyrospila (Walker)) and a new host, baldcypress (Taxodium distichum (L.)), were investigated in southern Louisiana where persistent annual defoliation over increasingly larger areas has occurred since 1983. Defoliation was observed to correspond with common types of baldcypress foliage morphology; designated as open and appressed. Pondcypress, Shumard oak and citrus foliage also were examined. The objectives were to: (1) determine the relative suitability/susceptibility of foliage types, and (2) quantify parameters of foliage quality possibly influencing FTLR performance. Levels of defoliation, egg mass counts, and laboratory bioassays of: initial survival, host preference, growth, feeding, and development, were used as measures of FTLR performance. Parameters of foliage quality included physical attributes, protein precipitating capacity, and concentrations of: nutrients, total nonstructural carbohydrates, and acid detergent fiber. Defoliation was linked conclusively to baldcypress foliage morphology. Open morphology trees consistently received higher levels of defoliation ($>$75%) compared to appressed types ($<$50%). No statistical differences were detected between the number of egg masses on these types, suggesting foliage quality influenced FTLR success. Results of laboratory bioassays indicated that open morphology baldcypress was clearly the most suitable/susceptible host. Shumard oak and sweet citrus were unacceptable hosts. Open morphology foliage was distinctly selected over appressed foliage and yielded the highest initial FTLR survival. In addition, female larvae consumed more foliage and yielded heavier pupae when reared on the open foliage. Host associated differences in pupal weights were attributed to observed differences in consumption and developmental periods because utilization of consumed foliage was not different among hosts. Host quality findings suggested that appressed foliage was a poorer host because of defensive characteristics deterring consumption. Pondcypress was of similarly lower suitability/susceptibility due to asynchronus phenological development and undetermined mechanism(s) causing early pupation of larvae. Favorable plant constituents for insects generally declined and negative constituents increased between early and late instar stages, indicating a decline in cypress foliage quality over time. Open morphology foliage was characteristic of smaller trees and persuant to this, young trees appear to be most likely to receive high levels of FTLR defoliation.

Pages

172

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