Date of Award

5-2007

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Stephen A. Woods

Second Committee Member

Frank Drummond

Third Committee Member

Frederick A. Servello

Abstract

Parasitic wasps (parasitoids) play an important role as natural enemies of insects and contribute substantially to world biodiversity (May, 1988), yet they have received relatively little attention outside of agricultural settings. Clearcut harvesting and herbicide (glyphosate) application are frequent and widespread disturbances in Maine forests that drastically alter the local environment. Parasitoids are particularly susceptible to disturbance for several reasons: 1) they are vulnerable to small changes in environmental conditions, 2) they occupy a high trophic level, and 3) many are host specific. However, there may be potential benefits of disturbance such as increased food resources (floral nectaries) and increased abundance and diversity of hosts. This thesis discusses a study of several wasp taxonomic families within managed forest in western Maine. To investigate the effects of clearcut timber harvesting and glyphosate application on parasitoids this study compared five forest treatment types to mature forest in western Maine (Somerset county). The forest types consisted of young (35 years since harvest) glyphosate treated clearcuts, young untreated clearcuts, old (1421 years since harvest) glyphosate treated clearcuts, old untreated clearcuts, plantations (1417 years since harvest, glyphosate treated, and planted with black spruce seedlings), and mature forest (more than 50 years old). Wasp communities were sampled using two malaise traps in each replicated forest treatment type throughout the summers of 2000 and 2001. To investigate the relationship between floral resources and parasitoid abundance in forest ecosystems, floral communities were sampled in each site along four 40m linear transects. Although not always significant, parasitoid abundance at the family level tended to be greater in plantations and lower in young clearcuts compared to mature forest. Braconidae abundance tended to be greater in old clearcuts compared to mature forest, but equivalent for other families. At the family level, parasitoid abundance was not affected by glyphosate. The effect of forest type on parasitoid morphospecies was inconsistent in 2000 and 2001. The effect of floral communities on wasp family abundance was inconsistent between years, but overall appeared to have no effect. However, the abundance of the native perennial plant, bunchberry (Cornus canadensis), was correlated with the abundance of Ichneumonidae, Braconidae, and Pompilidae, as well as several morphospecies. Chalcidoidea abundance was correlated with the abundance of wild strawberry (Fragaria spp.). Taken together, the results of this study suggest that clearcutting has an overall negative shortterm effect on parasitoid abundance, but a positive (particularly when replanted with spruce) or neutral longterm effect. These effects appear to be unrelated to floral community, but specific floral species may provide direct benefit or be indicators. Host availability, microclimate and habitat complexity are likely to be important factors to consider for future studies of this nature.

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