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English broom suppression with the broom twig-mining moth | LC0149 |
Keith Turnbull Research Institute, Frankston
December, 1998 |  |
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Common name
Broom twig-mining moth
Scientific name
Leucoptera spartifoliella (Hübner)
Family Lyonetiidae
Background
English (or Scotch) broom, Cytisus scoparius, is a Regionally Controlled weed in the Wimmera, Corangamite, Port Phillip East, Goulburn, North East, West Gippsland and East Gippsland Catchment and Land Protection Regions in Victoria. It is a threat to environmental, forestry and grazing lands in higher rainfall areas of south eastern Australia. A program is under way to introduce a number of natural enemies of English broom from Europe. Extensive testing of the broom twig-mining moth has demonstrated that it only feeds on English broom and does not attack native plants or plants of economic importance. The twig-mining moth was first released in Victoria in 1993.
Description
Adults - 2 to 4 mm long, silvery-white, with a small, dark brown and silver patch and fringing on the end of each forewing.
Eggs - white, oval-shaped, 0.5 mm long, laid singly in the furrows of young, green stems.
Larvae - six instars; mature larvae are about 3 mm long, olive-green with a dark stripe visible along the upper and lower body surface.
Pupae - enclosed within white, silky, spindle-shaped cocoons 6 mm long. Cocoons are found singly or in clusters depending on the density of the moth population, usually on the underside of green or dead twigs, and rarely in leaf litter.
Life cycle
The twig-miner has one generation per year. Adults usually emerge in early to mid December and live for 3 to 4 weeks. Time of emergence can vary with climatic conditions. Adults may be present until early autumn.
Figure 1. Adult twig-mining moth.
Figure 2. Pupal cocoons of twig-mining moth.
Egg laying occurs over the summer period. Each female may lay 70 to 120 eggs. A tiny, flat larva perforates the underside of the egg 15 to 18 days after oviposition. The larva eats into the outer covering of the stem, and proceeds to tunnel through the soft tissue beneath the bark. The larva progresses slowly, feeding on the green tissue and gradually enlarging its gallery, which fills with faecal material. The bark above the tunnel darkens to form raised purplish tracks on the stem surface, referred to as mines. The surface of the mine has a fine membranous appearance, as opposed to the rough scarring which may result from the feeding damage of other insects.
Figure 3. Twig of English broom with egg and mine of the twig-mining moth larva indicated by arrows.
Larval feeding and development continues throughout summer and autumn, slowing to a halt during the cooler winter months. Feeding resumes in spring. During the whole period of development a larva may tunnel 30 to 50 cm on an ascending or descending course, occasionally crossing over a stem rib and often switching furrows after passing through a node. In mid to late spring mature larvae exit the mines. They may spin their cocoons at the point of exit or wander about the plant dropping fine threads of silk before finding a suitable pupation site. The pupal stage lasts about one month, longer in cooler weather.
The cocoon is the most easily detected stage of the twig-miner, so the best time to determine if the insect is present is in late spring.
Impact
High numbers of L. spartifoliella result in the production of considerable areas of dead wood caused by larval mining. This impact may accelerate senescence of older bushes and reduce the amount of green tissue available for photosynthesis, stunting growth in younger plants.
No predators of the twig-mining moth are presently known in Australia or New Zealand. The insect can therefore exert greater pressure on broom than in its native Europe, where it is heavily parasitised. L. spartifoliella is common and widespread in New Zealand where it is having a significant detrimental impact on broom infestations. Impact in Australia has not yet been assessed.
Releases
Releases have been made in Victoria, NSW and Tasmania with establishment confirmed at several sites. Numerous releases have been made in Victoria, mainly in the Alpine National Park. Releases are made from the end of October to the beginning of November. Cocoons are harvested on twig cuttings from established sites and placed amongst broom stands at selected biocontrol sites.
Sites appropriate for biological control have a dense population of broom with actively growing bushes. The infestation size should be at least one hectare and there should be adjoining infestations to facilitate dispersal of the moth. The site should be excluded from other weed control measures.
Integrated control
The twig-mining moth alone will not control English broom. A suite of other insect biological control agents is expected to complement the damage caused by the moth and impose additional pressures on broom infestations.
There are two additional agents approved for biological control of English broom in Australia. Nymphs of the psyllid or plant louse, Arytainilla spartiophila, suck sap, stunting the growth of young shoots. It was first released in Australia in 1994 and has been released in New South Wales and Tasmania. The broom bruchid or seed-feeding beetle, Bruchidius villosus, has larvae which mine into developing seeds, reducing seed production. It was first released in Victoria in autumn 1998. Two other insects are being investigated as potential biological control agents. The seed-feeding weevil, Exapion fuscirostre, is expected to complement the activities of the bruchid, while the mite, Aceria genistae, forms galls on broom stems.
Biological control cannot eradicate a weed, it can only reduce the spread and density of infestations. In some cases control is achieved to the level where the weed is no longer of concern and no other control is necessary. More commonly, other methods are still required to achieve the desired level of control, however these need not be used so frequently or intensively. Biological control should not be considered the complete answer to an English broom problem, but can be used in conjunction with other control measures in an integrated weed management program.
Further Information
For further information on the management of English broom please contact your local NRE area staff or:
Keith Turnbull Research Institute,
PO Box 48, Frankston, Victoria, 3199.
Tel (03) 9785 0111
Fax (03) 9785 2007
Acknowledgments
Prepared by Nicole Freeman and Ian Faithfull (KTRI) and Peter Hodge (NSW Agriculture), January 1997. Revised by Ian Faithfull, November 1998.
Biological control of broom using the twig-mining moth is funded by NRE’s Catchment Management and Sustainable Agriculture and Parks, Flora and Fauna Divisions, the Australian Alps Liaison Committee and Parks Victoria. The biological control of broom program is supported by the Cooperative Research Centre for Weed Management Systems.
This note replaces note number BC0015
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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