Term of Award

Spring 1998

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Committee Chair

Daniel V. Hagan

Committee Member 1

Jonathan Copeland

Committee Member 2

Frank E. French

Abstract

The infestation levels of Nantucket pine tip moths (NPTM), Rhyacionia frustrana (Lepidoptera: Tortricidae), a common pine tree pest in the Coastal Plain of Georgia, were compared in plots of various ages which were intensively cultured (with periodic application of herbicides and pesticides) to those which were normal cultured (in which no treatment was given). Infestation levels were not significantly different in four of the five pairs of plots in a 17 month study from October 1996 to February 1998. In the pair in which significant differences were found, a chemical bum occurred in the intensively managed plot which destroyed much of the new growth on the pine trees and made them unsuitable for pine tip moth infestation.

Plots intensively managed were found to have fewer species of pine tip moth parasitoids than normal culture plots. This result, along with the similarity of pine tip moth infestation levels between normal and intensive treatments, indicated that intensive management in the study area may not be effectively reducing NPTM damage.

The guild of parasitoids of R. frustrana included eight hymenopteran and one dipteran species. Hyssopus rhyacioniae (Hymenoptera: Eulophidae) was the most abundant parasitoid comprising 54.5% of the collection. Other parasitoids collected included Lixophaga mediocris 17.3 %, Eurytoma pini 1.1%, Eupelmus cyaniceps 7.2%, and Bracon variablis 5.5%; other parasitoids were less than 5% of the total collection.

Synthetic pheromone lures were used to trap male NPTM. No overt relationship was observed between pine tip moth infestation levels and the number of male pine tip moths collected in the pheromone traps. A negative correlation was found between mean weekly relative humidity and pine tip moth adult emergence. Five generations of pine tip moths were observed during the 14 month (February 1997 to March 1998) study, four in 1997 and one in 1998.

Hyssopus rhyacioniae was attracted to various pine odors in a Y-tube airflow olfactometer. Hyssopus rhyacioniae did not show a preference for any particular pine species or turpentine odor in a choice assay. Nantucket pine tip moth larva, frass, and pheromones were not attractive to H. rhyacioniae in the olfactometer, but NPTM larva and frass stimulated an increase in the frequency of several behaviors by H. rhyacioniae in the arena after contact. These results suggest that H. rhyacioniae uses a combination of short and long range host location cues: the pine serves as the long range cue to draw H. rhyacioniae to a particular habitat, and then NPTM larva and frass serve as short range cues which stimulate an intensive search of a small area until the NPTM larval host is encountered.

When adult NPTM collected from both loblolly and Virginia pines were presented with a choice between these pines and other common pine species, adult NPTM preferred the species of pine that they normally infested (loblolly and Virginia) over slash and longleaf pines. The species of pine tree on which the NPTM was collected did not affect its choice in the olfactometer, suggesting that olfaction may play a role in the selection of trees to infest by NPTM.

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