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English broom suppression with the broom seed-feeding beetle | LC0164 |
Keith Turnbull Research Institute, Frankston
June, 1999 |  |
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Common and scientific names
Broom seed-feeding beetle, broom bruchid
Bruchidius villosus (Fabricius)
Family Bruchidae, seed beetles
Background
In Victoria 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. It is a threat to environmental, forestry and grazing lands in these Regions and other areas of south eastern Australia with moderate to high rainfall.
A program is under way to introduce a number of natural enemies of English broom from Europe. Extensive testing of the third of these agents, the broom seed-feeding beetle, has demonstrated that it only feeds on English broom and does not attack native plants. The seed-feeding beetle was first released in Australia in New South Wales in 1995.
Description
Adults – 2 to 4 mm long, black with longitudinal line patterning on wing covers, club-shaped antennae (Figure 1).
Figure 1. Adult broom seed-feeding beetle.
Eggs - 0.3 mm long, oval, very pale green, purplish when hatched (Figure 2).
Figure 2. Eggs (arrowed) on a broom pod.
Larvae - very small and hidden from view within developing broom pods.
Pupae - very small and hidden from view within broom seeds.
Impact
Female beetles lay eggs on the outside of broom pods and emerging larvae burrow through the pod to feed in the developing seeds, destroying them in the process. High numbers of bruchids reduce seed production, reducing the density of broom infestations and the rate of spread of the weed.
Life cycle
Adult broom seed-feeding beetles feed amongst the flowers of English broom (Figure 3). Pollen is required in order to attain sexual maturity. Eggs are laid singly or in horizontal rows of up to six eggs on the outside of developing broom pods. The eggs change from very pale green to a purplish colour when larvae have hatched. A very fine bluish line may be observed on the outside of the pod as the larva makes its way to a developing seed.
Larvae feed on the seed contents. They pupate within the outer skin of the seed. When the pod opens and the seeds are expelled, the bruchid is also expelled. Pupae overwinter within the shed seed. Adults emerge from the seed amongst leaf litter and make their way to the broom flowers to feed on pollen.
Figure 3. Adult broom seed-feeding beetle eating broom pollen.
Releases
Releases of the broom bruchid have been made in New South Wales and the Australian Capital Territory with establishment looking promising at all release sites. It was first released in Victoria in autumn 1998. Releases are made from the end of October to late November with adults that have recently emerged from hibernation, or in early autumn.
Appropriate sites have a dense population of English broom with actively growing bushes. Infestations should contain mature seed-producing plants, at least five years old. The infestation should be at least one hectare in size with adjoining infestations to facilitate dispersal of the beetle. The site should be excluded from other weed control measures to encourage establishment.
Integrated control
The seed-feeding beetle alone will not control English broom. A suite of other biological control agents is expected to complement the damage caused by the bruchid and impose additional pressures on broom infestations. There are two additional agents approved for biological control of English broom in Australia. The broom twig-mining moth, Leucoptera spartifoliella, was first released in 1990. Larvae of this moth mine in broom stems causing dieback and reduced growth. Nymphs of the psyllid or plant louse, Arytainilla spartiophila, suck sap, stunting the growth of young shoots. Releases of the broom psyllid commenced in 1995 in New South Wales and Tasmania. It is yet to be released in Victoria.
Two further agents are currently under investigation, the seed-feeding weevil, Exapion fuscirostre, and an eriophyid gall mite, Aceria genistae. Host specificity testing of these potential agents is still underway and they have not yet been approved for Australian release.
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 land management agency area staff or:
Keith Turnbull Research Institute,
PO Box 48, Frankston, Victoria, 3199.
Tel (03) 9785 0111
Fax (03) 9785 2007
Acknowledgements
Prepared by Nicole Freeman, Ian Faithfull and Raelene Kwong.
Biological control of broom in Victoria 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 BC0031
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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