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Arne Witt collecting leafhoppers at Breton Lake, South
Africa
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Background
In the early 1990s, surveys to identify potential biological
control agents for bridal creeper were undertaken in South
Africa, the native range of this plant. These surveys were
conducted to gather information on the distribution and phenology
of the potential biological control agents and in order to
assess their likelihood of establishing in Australia where
their host has naturalised and become a weed. The host-specificity
of selected candidate agents was demonstrated in subsequent
tests conducted in containment facilities in Australia. Three
biological control agents of bridal creeper have now been
released in Australia: the leafhopper
Zygina sp. in 1999, the rust
fungus Puccinia myrsiphylli in 2000 and the leafbeetle
Crioceris sp. in 2002.
Since the first agent was released, a concerted effort by
the CSIRO and CRC for Australian Weed Management, in collaboration
with community groups, schools and landholders, has led to
one of the most successful biological control programs in
Australia.
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Kathryn Batchelor and a school pupil who has been involved
in the rearing and release of the bridal creeper leafhopper
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A national redistribution program established in 2002, with
the financial assistance from the Natural Heritage Trust,
has fast tracked the release and spread of the leafhopper
and rust fungus across the entire range of bridal creeper
infestations. Over the years, CSIRO staff have been teaching
on-ground groups and landholders the basic skills to identify,
release and monitor the impact of the agents. Detailed information
about the agents and various protocols for release and redistribution
are accessible in the section 'The
Biocontrol Project'. A national database of release sites
which is linked to a web-based interactive map is used to
keep track of the releases made. Based on database entries
as of April 2005, the leafhopper and rust fungus have now
been released at a total of 856 and 1670, respectively, across
southern Australia (including releases made by DPI Victoria).
These however, underestimate numbers because not all collaborators
have provided details about the releases that they have made.
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Anthony Swirepik conducting a field day/workshop in
2002 training landholders on the release and monitoring
of bridal creeper biocontrol agents
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Both leafhoppers and rust fungus damage bridal creeper by
attacking the cladodes (leaves). The leafhoppers feed on mesophyll
cells and their damage is seen as white variegations on the
leaf surface. The rust fungus infects stems and cladodes and
is easily recognisable as yellow circular areas on the upper
side of cladodes and by corresponding orange sporulating pustules
on the under side. Severe infestations of both agents result
in reduced photosynthesis, premature defoliation and reduced
tuber production.
It is still early days for the Crioceris sp. leaf
beetle, the third agents released against bridal creeper.
Establishment has only been confirmed at a few sites in Western
Australia in 2004, but more work is required to determine
the best time and number of insects to release. The leaf beetle
has one to two generations/year, consumes young, expanding
cladodes and shoots and only lay eggs on shooting tips. Both
adults and larvae are particularly difficult to handle and
consequently this agent will be unsuitable for mass-rearing
by community groups and schools.
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