Native Insects as a Framework for Understanding Potential Impacts of Exotic Species
Date
2014
Authors
Garms, Brian
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Abstract
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.
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Keywords
biological control, Enemy Release Hypothesis, Agonoscelis rutila, Marrubium vulgare, Nyctemera amica, Senecio madagascariensis, Scirtothrips aurantii
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