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Cascading Ecological Impacts of Emerald Ash Borer: Tritrophic Interactions Between Prickly Ash, Giant Swallowtail Butterfly Larvae, and Larval Predators

Rice, Kevin Barry
http://rave.ohiolink.edu/etdc/view?acc_num=osu1366373364

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Entomology.
The introduction of emerald ash borer, Agrilus planipennis (EAB), into forests of Midwestern US and Southeastern Ontario forests has resulted in the death of millions of ash trees, Fraxinus spp. Large-scale canopy gaps created by ash mortality increases light reaching understory plants. The native understory shrub prickly ash, Zanthoxylum americanum, contains furanocoumarins, highly biocidal secondary metabolites, that deter most insect herbivores. Furanocoumarins are photoactivated, becoming more toxic when exposed to UV light (Berenbaum 1978). Furthermore, furanocoumarin biosynthesis is energy intensive, and their concentration increases when photosynthesis is enhanced by increased light availability. Theory predicts that female plants invest more resources in defense, while males allocate more towards growth. Therefore, male and female prickly ash growing in canopy gaps may differ in their furanocoumarin concentrations, growth rates, and reproductive effort. Giant swallowtail butterfly larvae, Papilio cresphontes, are specialist herbivores on prickly ash capable of detoxifying furanocoumarins. Energetic costs of furanocoumarin detoxification can slow larval development, and thus increase exposure to natural enemies. In a series of field and lab experiments, we examined the effects of EAB-induced canopy gaps on resource allocation of male and female prickly ash, and growth and survival of giant swallowtail larvae. Prickly ash growing in canopy gaps had lower specific leaf area (SLA) compared to shaded plants. Male plants grew more in sun compared to males in shade. However, females located in sun grew less than females in shade. Females produced more flowers than males, and canopy gaps increased total flower and fruit production. Therefore, male plants invested proportionally more resources towards growth, whereas females invested more in reproduction. Canopy gaps significantly affected physical defenses of prickly ash. Thorn length, thorn area, and width of thorns increased in gaps, and females produced higher thorns than males, but these patterns varied by year. We quantified furanocoumarins, total phenolics, and nitrogen concentration in sun and shaded foliage of male and female prickly ash using high performance liquid chromatography. Foliar total furanocoumarin concentrations were higher in sun plants than shade. Leaf nitrogen concentration was greater in male plants. In addition, we examined the effects of prickly ash foliage collected from understory and canopy gaps on the development of P. cresphontes larvae. Larvae that consumed foliage from plants growing in sun had lower relative growth rates compared to larvae feeding on foliage from shaded plants. Our results suggest P. cresphontes larval development is negatively affected by widespread canopy gap formation. There was no difference in survival of larvae placed on plants growing in sun or shade, with mortality over 48 hours close to 70% in both habitats. We predict, however, that giant swallowtail larval survival will be lower in EAB infested forests because gaps increase the toxicity of prickly ash resulting in decreased growth rates that will increase exposure time of larvae to natural enemies. This study represents an example of one of many indirect ecological impacts of the emerald ash borer induced ash mortality likely to cascade through invaded forests.
Daniel Herms, PhD (Advisor)
153 p.
Entomology
Emerald ash borer; EAB; indirect effects; plant defense theory

Recommended Citations

Citations

  • Rice, K. B. (2013). Cascading Ecological Impacts of Emerald Ash Borer: Tritrophic Interactions Between Prickly Ash, Giant Swallowtail Butterfly Larvae, and Larval Predators [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366373364

    APA Style (7th edition)

  • Rice, Kevin. Cascading Ecological Impacts of Emerald Ash Borer: Tritrophic Interactions Between Prickly Ash, Giant Swallowtail Butterfly Larvae, and Larval Predators. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1366373364.

    MLA Style (8th edition)

  • Rice, Kevin. "Cascading Ecological Impacts of Emerald Ash Borer: Tritrophic Interactions Between Prickly Ash, Giant Swallowtail Butterfly Larvae, and Larval Predators." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366373364

    Chicago Manual of Style (17th edition)

osu1366373364
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This open access ETD is published by The Ohio State University and OhioLINK.