broom twig- mining moth

Weed Biological Control Pamphlet No. 9
April 2008
BIOLOGICAL CONTROL OF ENGLISH BROOM:
MINING MOTH
BROOM TWIG-
Background
English broom, Cystisus scoparius (also known as
broom and Scotch broom) is a leguminous shrub that
is native to central and western Europe and has now
spread to many temperate areas of the world.
English broom has now become naturalised over
large areas of south-eastern Australia.
In Tasmania, it occurs throughout areas of human
settlement but is particularly common in higher
rainfall areas. Plants are locally abundant on
roadsides, waste areas, poor quality pastures and in
disturbed bushland. In pastures, English broom
causes production losses by forming thickets that
prevent grazing.
Mature bushes are relatively
unpalatable to sheep and cattle and contain alkaloids
that are potentially toxic to stock. Dense thickets
also provide cover for pest animals such as rabbits
and inhibit access to bushland and recreational areas.
English broom can be controlled to varying extents
by herbicides, burning, mechanical clearing and
grazing using sheep and goats. Grazing with sheep
and goats is effective in pasture situations. However,
the limited success, expense and difficulty in
controlling English broom in many areas has resulted
in biological control being investigated.
Many insect species have been recorded on
English broom in its native range and several of
these have been under investigation to determine
whether they have a sufficiently narrow host range to
enable them to be released safely in Australia as
biological control agents.
These investigations
resulted in the broom twig-mining moth, Leucoptera
spartifoliella, which occurs in northern and central
Europe, being released in New South Wales in 1993.
It has since been released in Victoria and is now
established on English broom in both states.
The moth was released in Tasmania in 1995 and
again in 1998, but there is no evidence that the moth
established from these releases. However, field
collected stock was again imported from southern
NSW in November 2004. Some of this consignment
was released directly into the field at a site near
Oatlands in December 2004. The remaining stock
was used to commence glasshouse rearing at New
Town Laboratories. Moths produced from this
culture are being used for field releases to get the
broom twig-mining moth widely established in
Tasmania.
If this program is successful, the
established sites will be used to collect and
redistribute the moth to sites around the state in order
to accelerate its dispersal.
Description, life cycle and biology
The moths (adult stage) (Fig. 1) are small, 3-4mm
Figure 1. Broom twig-mining moth (Photo: W.
Chatterton, TIAR).
long and mostly white, with dark markings near the
tips of the forewings. There is one generation each
year. The moths start to emerge from pupae in early
summer (December), with numbers reaching a peak
around mid-summer (January).
Eggs are white and oval shaped about 0.5 mm long
and laid singly in the furrows of young stems. They
hatch over a period of 2-3 weeks. The tiny, flat,
legless larvae perforate the underside of the egg,
bore into the stem and then tunnel through the tissue
beneath the bark. Mature larvae are about 3 mm
long, olive green with a dark stripe visible along the
upper and lower body surface.
Larval feeding continues throughout the remaining
summer and autumn but slows and may cease during
the cooler winter months. Feeding resumes in spring
with fully developed mines often reaching 30-50 cm
in length. The larvae pass through six stages
(instars) during their development. First and second
instar larvae are very small. Mines created by these
young larvae are no more than 10 mm long and only
about 0.5 mm wide. They are therefore difficult to
see with the naked eye. Once the mines reach 30
mm in length, the mine is 0.5-1mm wide and more
readily visible. Most damage to the plant is caused
by the fifth and sixth instar larvae in spring, at which
stage the mines become raised and up to 2 mm wide
(Fig. 2).
During spring, from about October, the fully
developed larvae leave their tunnels and spin a white
cocoon (Fig. 3) from which the moths emerge.
When broom plants are heavily infested, the stems
become covered with white cocoons. In general, the
pupal period lasts about one month, but may be
longer depending on weather conditions.
Figure 2. Stem mines caused by larvae of the broom
twig-mining moth (Photo: W. Chatterton, TIAR).
Although larval feeding activity will not by itself
be capable of controlling English broom, it has the
potential of causing considerable damage to the
plant, weakening it and making a useful contribution
to its control. Introductions of more biological
control agents are planned and these will place
additional stress on plants, reduce their vigour and
ultimately decrease the density of infestations.
Biological control should be considered as a longterm program that is best used on large, chronic
infestations with a low priority for control by other
methods.
Acknowledgments
CSIRO and NSW Agriculture conducted the host
specificity testing and importation for the broom
twig-mining moth that enabled its initial release in
Australia. CSIRO and DPI, Frankston, Victoria
provided information on the biology of the moth.
Figure 3. Pupa of broom twig-mining moth (Photo:
W. Chatterton, TIAR).
Damage
Branches that become heavily infested with
tunnelling larvae can die. With continued heavy
attack, plants become less vigorous and display a
large amount of dead wood. Plant growth and seed
production can be significantly reduced.
For further information on this project contact:
John Ireson
Tasmanian Institute of Agricultural Research,
13 St. John’s Avenue, New Town, 7008.
Phone: (03) 6233 6821; Fax: (03) 62782716
Email: John.Ireson@dpiw.tas.gov.au