Native Insects as a Framework for Understanding Potential Impacts of Exotic Species
Creators: name: Garms, Brian
Publisher: name: The Australian National University
Year: 2014
Subjects: biological control
Enemy Release Hypothesis
Agonoscelis rutila
Marrubium vulgare
Nyctemera amica
Senecio madagascariensis
Scirtothrips aurantii

description: The problem of managing exotic species in new habitats is large and complex. Many different working theories have been developed to attempt to understand and predict impacts of exotic species in new environments, either as unintentional introductions or as intentional introductions such as biological control agents. Invariably such theories have had mixed support and there is no single theoretical framework for accurate predictions of the impact (either positive or negative) of exotic species. Nevertheless, development of theory is an active area of research as predictions of future impacts of exotic species are critical for directing resources to best maintain ecosystems of value to humans. This thesis looks to develop new experimental approaches for understanding and predicting potential exotic species impacts. Native species are demonstrated to be an effective tool for experimentally determining both what type of exotic species impacts are possible and the minimum biological parameters an exotic must have to generate these impacts. Three systems are investigated to demonstrate the application of this approach in multiple systems. In Chapter 2 Scirtothrips aurantii is investigated as an invasive species and potential future pest in Australia. This recent invader has not attacked many potential host plants in Australia despite doing so in its native range. The results of this chapter show that the biology of this insect and its host selection behaviour suggest it could become a pest in the future. However the results also highlight the limitations of a study focussing on the invasive species alone, and how such findings need to be placed into a local context, in this case with native Australian Scirtothrips species. In Chapters 3 and 4 the impact of the native magpie moth (Nyctemera amica) on invasive fireweed (Senecio madagascariensis) is studied. In Chapter 3 the biology and host selection behaviour of the moth show that fireweed is a suitable host, but moth host preferences vary based on their local population and may point to changing utilization of fireweed over time. In Chapter 4 herbivory by magpie moth larvae is shown to reduce the fitness of fireweed in the lab and the field. These findings are counter to the predictions of the Enemy Release Hypothesis (ERH) and the implications for selection of biological control agents of fireweed are discussed. In Chapters 5, 6 and 7 the biology of the horehound bug (Agonoscelis rutila) and its impacts on horehound (Marrubium vulgare) are investigated. In Chapter 5 horehound bug adults and juveniles are shown to feed on seeds. In Chapter 6 the potential of the horehound bug to pollinate horehound is investigated. The insect does not provide any pollination services; its effect on horehound seed set is strictly negative. However, significant variation in between-plant pollination rates is documented. Finally, in Chapter 7 the survival of horehound nymphs and their reduction of horehound seed survival in the field are studied, and the implications for ERH and biological control are discussed.