Semester

Fall

Date of Graduation

2021

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Wildlife and Fisheries Resources

Committee Chair

Christopher M. Lituma

Committee Member

Christopher T. Rota

Committee Member

William K. Oldland

Committee Member

Scott H. Stoleson

Abstract

Non-native invasive insect pests can have dramatic impacts on native ecosystems, feeding on plant foliage, wood, or sap. Little is known, however, about how fruit-targeting NNIIPs may affect native ecosystems. Spotted wing Drosophila (Drosophila suzukii Matsumura, SWD) is a recently introduced invasive vinegar fly that parasitizes the fruits of many plant species in the United States. While its activity in agricultural systems is well-documented, little is known about its activity in forest ecosystems, despite growing evidence of its presence and parasitism of fruits there. Parasitism could reduce fruit attractiveness for vertebrate fruit consumers, including migratory birds. As such, this may reduce soft mast food availability for birds in early successional habitat during the post-breeding season and fall migration, interfering with energy accumulation when demands are greatest. This thesis includes 4 chapters focused on understanding factors influencing SWD in invaded forest habitat and whether SWD activity associates with avian abundances, species richness, body condition, and fruit consumption at Allegheny National Forest in northwestern Pennsylvania.

In Chapter 1, I provide context and justification for this research. I first describe how NNIIPs are known to influence forest ecosystems. I then review information on how SWD affects fruit crops in agricultural systems and provide a framework detailing how fruit parasitism by SWD may alter forest ecosystems. I lay out the research on fruit parasitism and fruit consumption by wildlife, especially fruit-consuming birds. I relate this to cascading effects on the following: 1) seed dispersal, 2) forest community structure and composition, and 3) food resources for wildlife. Finally, I highlight important research needs to uncover how SWD may affect forest ecosystems.

In Chapter 2, I investigate how SWD distribution and abundance are influenced by forest composition, with respect to dominance by black cherry (Prunus serotina), a highly parasitized host, and local fruit resources in a forested ecosystem. From July to October 2019 and 2020 I trapped SWD in 21 regenerating timber harvests and surrounding forest canopies, representing 2 different cover types, and I collected Allegheny blackberry (Rubus allegheniensis) fruit samples in those regenerating timber harvests to observe for emergence of SWD. Relative abundance of SWD in regenerating timber harvests and surrounding forest canopy correlated to host resources at the local (i.e., sampling point) level but not the adjacent cover type. Parasitism of R. allegheniensis fruits positively correlated with local R allegheniensis fruits and basal area of P. serotina in adjacent mature forest. The results of this study provide the first evidence for the importance of local resources over those in an adjacent cover type or surrounding forest for predicting SWD trap captures, and the importance of local fruit resources and host plant density in adjacent cover type for SWD fruit parasitism in invaded forest ecosystems. I suggest these relationships can help predict the timing and abundance of SWD in both natural and semi-natural systems where wild fruiting plants are abundant, providing valuable information for monitoring and management planning.

In Chapter 3, I identify factors, primarily those related to SWD abundance and fruit parasitism, influencing frugivorous and non-frugivorous bird relative abundance and species richness in regenerating timber harvests invaded by SWD during the post-breeding season and fall migration. From July to September 2019 and 2020 I sampled bird communities using mist net captures in 21 regenerating timber harvests, and I trapped SWD and sampled R. allegheniensis fruits for SWD parasitism at each mist net. One species, eastern towhee (Pipilo erythrophthalmus), correlated negatively with SWD trap captures. Two species, hooded warbler (Setophaga citrina) and ovenbird (Seiurus aurocapilla), correlated negatively and positively to parasitism of fruits, respectively. Post-breeding and migratory bird relative abundances were otherwise unrelated to SWD variables in regenerating harvests. Frugivorous birds either did not alter fruit consumption in response to SWD, or birds’ abilities to alter diet and foraging behavior masked relationships to SWD. Eastern towhee likely perceived fruits covered with flies as less desirable for consumption or may have been deterred by SWD swarms. Ovenbirds and hooded warblers altered their fruit consumption based on their responses to parasitism in modeling results. Alternatively, SWD activity may have affected arthropod communities, shifting composition and affecting some birds via trophic cascading effects. I highlight the importance of investigating arthropod community responses and the actual consumption of fruit resources in habitats invaded by SWD as critical next steps to understanding the ecological effects of SWD.

In Chapter 4, I evaluate how factors, primarily those related to SWD abundance and fruit parasitism, relate to body condition of several bird species, and probability of fruit consumption by frugivorous birds in regenerating timber harvests invaded by SWD during the post-breeding season and fall migration. From July to September 2019 and 2020 I gathered data on body condition indices—subcutaneous fat, feather molt progression, and scaled mass index (SMI)— and collected fecal samples for evidence of fruit consumption for individuals of several bird species captured using mist nets in 21 regenerating timber harvests. I also trapped SWD and sampled R. allegheniensis fruits for SWD parasitism at each mist net. Multiple condition indices for several species correlated with relative abundance of SWD and parasitism of fruits, though the directions of relationships varied and were species-specific. Probability of R. allegheniensis fruit consumption by frugivorous birds correlated positively with parasitism of fruits at both the guild and species level. Frugivorous birds were more likely to consume parasitized fruits, and one species, gray catbird, experienced changes to nutritional intake and subsequent condition as a result. Fruit parasitism and greater abundances of adult SWD may have altered arthropod communities, altering composition and changing an additional food resource for both non-frugivorous and frugivorous birds. Most species improved condition indices as the season progressed, likely due to dietary flexibility. I list several critical avenues for research to better understand the relationships observed in this study: 1) how bird condition changes in relation to foraging microhabitat selection and SWD, 2) selection or rejection of SWD-parasitized fruits by frugivores related to nutritional metrics, and 3) arthropod community responses to SWD.

Download

Share

COinS