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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Environmental Conservation

Year Degree Awarded

2017

Month Degree Awarded

May

First Advisor

Joseph Elkinton

Subject Categories

Entomology | Forest Management | Other Ecology and Evolutionary Biology | Population Biology

Abstract

Gall wasps are phytophagous insects that often go unnoticed, however, when they are released from their natural enemies, they have the capacity to outbreak and cause extensive foliar damage. One such outbreaking pest, Zapatella davisae, causes significant damage and mortality to black oak, Quercus velutina. In recent years, black oak decline has been documented in Long Island, New York and coastal New England. Little is known about the lifecycle, distribution or population dynamics of Zapatella davisae and the taxonomy of the species is still unclear.

My first study described the biology and distribution of Z. davisae. Zapatella davisae completed one life cycle per year, and emerged in early May. The same proportion of trees were infested in Cape Cod and Long Island, however, the severity of the infestation was significantly greater in Cape Cod, an indication that something may be regulating populations in Long Island.

I evaluated where Z. davisae fits within the Cynipidae phylogeny, quantified genetic diversity across geographically isolated populations and identified which loci gave the most taxonomic clarity. Three genes determined that Z. davisae is completely invariant across all geographically isolated populations, likely indicative of a founder effect. Zapatella davisae may be native, as it was a species-level match to a gall wasp species from the southeastern, US. LWRh and COI gave the most taxonomic clarity, as they had genera that fell out into distinct clades, whereas 28S increased the incidence of polyphyletic and paraphyletic clades.

After I determined Long Island and Cape Cod populations were both Z. davisae, I compared the population dynamics in each location. On Long Island, multiple gall wasp populations exhibited almost 100% parasitism in 2015, which was followed by a near total collapse of the population in 2016. On Cape Cod, parasitism rates were lower and consistent overtime, which may explain greater canopy damage in that region. On Long Island, species-group Sycophila species 3 caused the highest level of parasitism, but parasitism from this species was lower on Cape Cod. My results indicate that Z. davisae populations are controlled by top-down pressures on Long Island.

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