Masters Theses

Date of Award

12-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Jerome F. Grant

Committee Members

Charles D. Pless, Paris L. Lambdin

Abstract

The pyralid Dicymolomia julianalis (Walker) has an unusually diverse range of hosts, yet relatively little information is available on this lepidopteran. Food sources of the pyralid larva include musk thistle, Carduus thoermeri, eggs, larvae and pupae of the common bagworm, Thyridopteryx ephemeraeformis, and cat-tail, Typha spp.

A study was initiated to better understand the ecological interactions among D. julianalis and its hosts by monitoring the lifecycle of this pyralid and assessing its feeding habits. The potential of D. julianalis as a biological control agent of musk thistle and the common bagworm was also examined.

Adult D. julianalis moths were reared in the laboratory from field-collected samples of musk thistle, bagworm, and cat-tail. Life-history assessments were made based upon dissections as well as adult emergences from field-collected samples. During this two-year study, three distinct generations per year of D. julianalis were observed in eastern and middle Tennessee. The first generation, occurring from mid-March to late October, was found on cat tail. The second generation was present on dead or dying musk thistle from early June to mid-October. Second-generation individuals were also reared from cat-tail. The third and overwintering generation occurred inside bagworm egg clusters from early October to late May.

The greatest level of infestation (near 100%) of D. julianalis occurred on cat-tail seed heads. A high level of pyralid density, combined with the occurrence of D. julianalis on cat-tail for two consecutive generations, indicate that cat-tail is a preferred host for D. julianalis. During this two-year study, infestation levels, averaged across all sites, were 11.63 and 12.63% on musk thistle and bagworm, respectively.

Dicymolomia julianalis larvae were found in dead and matted musk thistle heads which rarely contained viable seeds; therefore, larvae were probably feeding on dead filaments within the seed heads. It was unclear, however, whether the pyralid larvae caused the thistle seed heads to become matted, or if ovipositing females selected damaged plants. Larvae of this species were not found on seed heads until June, however, at which time many of the plants had already reached maturity. This would indicate that the presence of the larvae did not have an adverse effect on the weed. If the larvae are present on the thistle plants too late to have any effect on the plant's reproductive ability, D. julianalis larvae are not likely to have potential in a biological control program directed against musk thistle.

Dicymolomia julianalis could have potential as a tool for biological control of bagworm. However, due to the pyralid’s relatively low level (12.8%) of infestation on bagworm, and the high number of eggs which remain in the bag after the pyralid emerges, their impact on reducing population densities of bagworm may not be meaningful. Further study is needed to better understand the ecology of this moth and its potential as a biological control agent of the common bagworm.

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