March 2002, Volume 23 No. 1
In this section we welcome all your experiences in working directly with the end-users of arthropod and microbial biocontrol agents or in educational activities on natural enemies aimed at students, farmers, extension staff or policymakers.
The South African plant bridal creeper, Asparagus asparagoides, has made an impact in Australia and is listed as one of the twenty Weeds of National Significance. It was deliberately introduced in the mid 1800s owing to its popularity in bridal bouquets, and with the help of birds eating its berries and spreading its seeds, it is now slowly smothering its way across southern Australia. In severe infestations the foliage smothers all vegetation to a height of 2-3m. However, above-ground parts form only a fraction of the plant: the vast majority is hidden underground in the form of tubers. Its marked impact is being felt severely throughout numerous national parks and in some cases it is threatening the existence of Australian native species.
Bridal creeper is now a target of two biological control agents that have been introduced, by the Cooperative Research Centre (CRC) for Australian Weed Management and CSIRO Entomology, in an attempt to bring it under control. The first, a leafhopper, Zygina sp, was released in July 1999. [See also BNI 20(4) 108N-109N (December 1999) `Green giant'.] Its most dramatic impact has been seen in Western Australia (WA) where large areas of bridal creeper have turned white through the insect's sucking activity. Similar results are also being found in South Australia (SA) and New South Wales (NSW).
WA is also the site where thousands of schoolchildren have embraced this biological process, rearing and distributing as many insects as possible under the guidance of Technical Officer Ms Kathryn Batchelor and project leader Mr Tim Woodburn. The results have been overwhelming. By the end of 2000 over 40 schools and community groups had become involved in the campaign in WA and by the end of 2001 the numbers had climbed to more than one hundred.
The attack from the leafhoppers prevents the plant from photosynthesizing and causes it to gradually use its stored energy from the tubers, making them shrink. The continued shrinking of the tubers will give native plant seeds a greater opportunity for germination and establishment than is currently the case.
There are numerous generations of the leafhopper every year and this gives the insect the ability to build up numbers rapidly. However, more than one biological control agent is required and in July 2000 the rust fungus, Puccinia myrsiphylli, was released. The rust completes its life cycle on bridal creeper, infecting the leaves and stems. It obtains nutrients and water from the plant thus limiting resources available for the production of stems, fruit and tubers.
The fungus also destroys leaf tissue by reducing the photosynthetic surface of the plant, causing severely diseased plants to shed infected leaves prematurely. In the winter rainfall regions of South Africa, the rust is usually observed within 12 weeks of appearance of new shoots in autumn. From then on, the incidence of the rust steadily increases during winter to reach its peak in spring when the plants are flowering and fruiting.
Weed CRC/CSIRO pathologist Dr Louise Morin is in charge of the pathology work and has praised the efforts of community groups so far, all of which have had a big role to play with the distribution of both the leafhopper and the fungus. The importance of this role is only going to increase in the future.
CSIRO has recently received funding from the Natural Heritage Trust which will allow more community groups to get on board the redistribution process and help release and spread these agents across bridal creeper infested sites in a much more rapid and coordinated manner. The funding will allow these groups to be trained by CSIRO staff to develop the basic skills and understanding they will require. It will also allow for the development of release information kits outlining the processes, maintenance of a national database on release sites and further enhancement of the bridal creeper website (see below).
As well as the work being undertaken by Kathryn Batchelor, the Weed CRC's Mr Anthony Swirepik has been the National Redistribution Coordinator for biological control agents for the last 6 years and has a major role to play in this project. Swirepik's job will involve making further contact with appropriate groups, organizing biological agents for them to release, liaising with them to ensure all is going well, and determining the level of monitoring that is required. The monitoring will allow researchers to determine how quickly the agents are spreading and what other areas need to have releases made to ensure rapid coverage of bridal creeper infestations.
Control of massive environmental weeds such as bridal creeper can only be achieved with community support. Since the late 1980s CSIRO has been developing close relationships with groups that have an active interest in biological control. From humble beginnings, national programmes have now been developed and the future of some target weeds is looking bleak. This is a situation that could not have been achieved without the efforts of the community and the state departments that have been involved.
There remains one more agent to be released against bridal creeper, the leaf-beetle Crioceris sp., and an application for its release is now being assessed by regulatory authorities. Both adults and larvae of this beetle feed on the young shoots and leaves of bridal creeper. It has one generation a year and is active during the autumn and early winter months when bridal creeper is commencing its rapid growth stage. All three biocontrol agents co-exist on the plant in its native South Africa, hence researchers anticipate that the action of these three agents will combine to bring around the future demise of bridal creeper.
Groups interested in the bridal
creeper research programme are encouraged to check out the web site at:
Contact: Kate Smith, CSIRO
Entomology, GPO Box 1700, Canberra, ACT 2601, Australia