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Leaf-rolling moth (Tortrix sp.)
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Leaf-rolling moth, Tortrix sp.
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The leaf-rolling moth (Tortrix sp.) is the most damaging
insect feeding on bitou bush in its home country of South
Africa. In Australia and South Africa, CSIRO Entomology and
the Keith Turnbull Research Institute have completed extensive
host specificity testing. Two strains of the leaf-rolling
moth have been collected. The other strain is specific to
the closely related boneseed (Chrysanthemoides monilifera
spp monilifera). In South Africa, the leaf-rolling moth
has not been found on any other plant species except bitou
bush and boneseed.
Background
A collaborative project between CSIRO Entomology and NSW
Agriculture (funding by Natural Heritage Trust) has commenced
to rear, release and evaluate the performance of the leaf-rolling
moth. The first release of the leaf-rolling moth on bitou
bush was near Grafton NSW in 2001. Subsequent releases have
been made along the NSW coast from Moruya in the south to
the Queensland border.
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Releasing Tortrix
on bitou bush
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To date the process has focussed on the release of egg batches
and larvae. Egg batches, which have been laid on cardboard
or leaves are released by stapling them face down onto leaves
at the site. Branches of bitou bush containing larvae are
attached with twitch wire, or simply laid across branches
at the release site. The larvae are mobile and quickly move
off the dying branches onto the new food source.
The release process has experienced poor establishment rates
at release sites, predation was identified as an important
factor in this. To quantify the effects of predation a field
experiment was carried at at Jervis Bay during autumn 2002.
Refer to the poster "Where
did all the Tortrix go" (PDF 859Kb).
The Project
The lifecycle (egg to adult) of the leaf-rolling moth takes
about 8 weeks to complete (longer in the coller winter months
and probably a bit shorter in the warmest summer months).
Eggs hatch after 8 days and the larvae move to the shoot tips
to begin feeding. The larval stage lasts about 30 days, pupa
10 days and adults 14 days. In the field in South Africa,
there are peaks in egg production during July, November and
late January.
The larvae feed on leaves, stems and surfaces of young shoots
resulting in death of shoot tips. High larvae populations
in summer, when the insect is most active, may severely defoliate,
weaken or kill plants. Revegetation strategies may need to
be implemented to stablise sites severely affected by the
leaf-rolling moth. In South Africa, the leaf-rolling moths
suffers heavy attack from predators and specialised parasites.
The quarantine process excludes the release of these natural
enemies in Australia, however native predators and parasites
may adapt and reduce its effectiveness.
Life Cycle of bitou bush
leaf-rolling moth
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Egg
Egg batches are green to yellow when first laid, then
turn orange and just before hatching the black head
capsules of the larvae are clearly visible. The batches
are flat and covered with a transparent film, which
remains after the larvae hatch. Egg batches can be found
on both the upper and lower surface of the leaf.
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Larvae
Larvae have 5 or 6 instar stages. First instars have
an orange body and dark head. As instars develop their
light brown head colour changes to orange. Their body
becomes yellow/green to olive green. Later instars develop
dark green to black bodies with stripes of small white
spots. Larvae feed inside a shelter formed by binding
leaves together with silk. The larvae can also drift
around on silk threads to move to fresh foliage. When
disturbed larvae wriggle vigorously and may drop from
the plant.
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Adult
Adults camouflage well with the damage caused to bitou
bush after larval feeding. They are most active at night,
especially the males. Adult females lay about 7 batches,
totally approximately 200 eggs per female.
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Å
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Pupa
Pupae are found in the larval shelter.
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Key People
Anthony Swirepik
CSIRO Entomology
Clunies Ross St Acton
GPO Box 1700
Canberra ACT 2601
Australia
Collaborators
Keith
Turnbull Research Institute
NSW
Agriculture
More Information
Where did all the Tortrix
go? (pdf 859Kb)
Monitoring for the
establishment of leaf rolling moth Tortrix sp. (pdf
1.08MB)
Targeting Bitou Bush (pdf
4.6MB)
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