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Biological Control of Bitou Bush: Just Around the Turn of the Millennium?

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Biological Control of Bitou Bush: Just Around the Turn of the Millennium? Twelfth Australian Weeds Conference BIOLOGICAL CONTROL OF BITOU BUSH: JUST AROUND THE TURN OF THE MILLENNIUM? Royce H Holtkamp1, Penelope B Edwards2 and Robin J Adair3 CRC for Weed Management Systems 1 NSW Agriculture, RMB 944, Calala Lane, Tamworth, NSW 2340 2 CSIRO Entomology, PMB 44, Winnellie, NT 0822 3 Keith Turnbull Research Institute, PO Box 48, Frankston, Vic. 3199 Abstract Bitou bush, Chrysanthemoides monilifera bitou bush to invade native vegetation was then rec- subspecies rotundata, is a native of South Africa, used ognised and its recommendation for coastal planting extensively in Australia as a sand stabilising plant and was withdrawn. However, by 1976 bitou bush was for revegetation of coastal areas mined for mineral naturalised along much of the NSW coast. Aerial sur- sands. It has now become a serious environmental veys of the NSW coastline were conducted by the NSW weed in eastern Australia, primarily of conservation National Parks and Wildlife Service in 1981 and 1982. areas, where it significantly reduces biodiversity. This These indicated that bitou bush was distributed along importance has been recently recognised with the list- approximately 60% (645 km) of the coast and was the ing of C. monilifera as a Weed of National Signifi- dominant species along 230 km. Since these surveys cance. A biological control program against C. its range has expanded and it has been predicted that monilifera was approved in 1987 and agent releases bitou bush has the potential to spread and occupy over commenced in 1989. To date, five species of insects 90% of the NSW coastline by 2010. Over approxi- have been released on bitou bush and additional spe- mately two thirds of this area it could completely domi- cies are under investigation. Of these insects, bitou nate and eventually displace most of the existing na- tip moth, Comostolopsis germana and bitou seed fly, tive vegetation. Mesoclanis polana have been the most successful. The importance of bitou bush was officially recognised Biological control is a long term program and will not in early 1999 by both the NSW National Parks and eradicate the host plant. An integrated approach ap- Wildlife Service who listed it as a key threatening proc- pears to be the best option for long-term sustainable ess under the Threatened Species Conservation Act control. The Cooperative Research Centre for Weed 1995 and by the Commonwealth of Australia who listed Management Systems is coordinating studies on inte- it as a Weed of National Significance under the Na- grated control of bitou bush which include the use of tional Weeds Strategy 1997. biological control agents together with strategic her- bicide applications, fire and revegetation techniques. Bitou bush is largely an environmental weed as it is easily controlled by stock grazing and cultivation. It is THE PROBLEM primarily restricted to non-agricultural areas such as Bitou bush, Chrysanthemoides monilifera subspecies national parks, forests, coastal dune ecosystems and rotundata (DC.) T. Norl., is a competitive environmen- other recreational land. In invaded vegetation, signifi- tal weed of South African origin. It is primarily re- cant reductions in biodiversity can occur. In the past, stricted to areas of summer rainfall (Parsons and physical and chemical control and fire have been used Cuthbertson 1992) and infests coastal areas of south- to reduce infestations and limit spread of bitou bush. ern Queensland, New South Wales (NSW) and Lord These traditional techniques are limited in their use Howe Island. There is also a localised infestation at for bitou bush control for a number of reasons. Physi- Menindee Lakes, NSW. In NSW it is common in ar- cal control techniques are extremely labour intensive eas north of Sydney and occurs south to the Victorian and can usually only target small areas. They are thus border. highly suitable for areas of high conservation signifi- cance. Herbicides have proven to be extremely effec- Bitou bush was first recorded in Australia from tive for broad scale bitou bush control (Toth et al. Stockton near Newcastle in 1908 (Weiss et al. 1998) 1996). However, there a number of situations where where it appears to have been an accidental introduc- they are not suitable, such as in the presence of rare or tion in ships ballast. From 1946 to 1968 bitou bush threatened flora. Fire is also not suitable for all areas was used as a sand stabilising plant and to revegetate because ecosystems such as coastal dunes and rainfor- coastal areas mined for mineral sands. The capacity of ests are not fire adapted. These techniques need to be 667 Twelfth Australian Weeds Conference repeated annually if they are to run down the existing a total of over 1200 km of coastline (Edwards et al. soil seed banks. Because of these limitations another 1999). Over much of this area, population levels are solution is required. extremely high and reductions in seed production of 50% are common. Further experiments on this species BIOLOGICAL CONTROL: THE ANSWER? are continuing. A biological control program against C. monilifera Research on establishing or introducing additional bio- (which includes bitou bush and boneseed, a closely logical control agents is continuing. Another species related subspecies) was approved by Standing Com- of seed feeding fly, M. magnipalpis has been released mittee On Agriculture in 1987. Surveys in South Af- onto boneseed in Victoria and South Australia. This rica have indicated that there are more than 100 spe- insect is also suitable for release onto bitou bush, es- cies of phytophagous insects associated with the pecially on the NSW South Coast and future plans in- Chrysanthemoides species complex (Scott and Adair clude its continuing redistribution. 1990). Eighteen of these species were identified as having potential for the biological control of C. Agents currently undergoing quarantine evaluation are monilifera and five species have so far been released a leaf feeding moth, ‘Tortrix’ sp., an eriophyiid mite, on bitou bush: bitou tip moth, Comostolopsis germana Aceria neseri and a rust fungus, Endophyllum Prout; black boneseed beetle, Chrysolina sp. 1; painted osteospermi (Doidge). Host specificity testing of boneseed beetle, Chrysolina sp. 2; bitou tortoise bee- ‘Tortrix’ sp. is now complete and an application for its tle, Cassida sp. and bitou seed fly, Mesoclanis polana release will shortly be submitted. By the end of this Munro. year we should know if ‘Tortrix’ sp. has been approved for release. The other two agents are a little further Of the above five insects there have been some suc- down the track but will hopefully be available for re- cesses and some failures. Chrysolina sp. 1 and lease early in the new millennium. Chrysolina sp. 2 have each been released at several sites along the NSW coast. Neither species has estab- DISCUSSION lished at any of these sites. Releases of Cassida sp. are Biological control will not eradicate bitou bush. At best continuing on the NSW North Coast and populations biological control will reduce this weed to a minor are persisting at some of these sites. The Australian component of invaded vegetation. The answer for long ant fauna is particularly large and diverse (Shattuck term control of bitou bush would appear to be an inte- 1999) and the larvae of these leaf-feeding beetles ap- grated weed management (IWM) approach using strat- pear to be particularly prone to predation by ants and egies such as biological control, physical removal, spiders (R.H. Holtkamp and R.J. Adair pers. obs.). This herbicides and fire. Studies on IWM are currently be- factor may have been important in limiting their po- ing coordinated by the Cooperative Research Centre tential as biological control agents. for Weed Management Systems. Any integrated pro- The other two species have been significantly more gram which incorporates biological control will have successful. C. germana has been released at over 70 to ensure that sufficient agents remain following other sites in NSW. It is now established along most of the forms of treatment for re-establishment of biological NSW coast and it is believed that this insect has spread control agent populations. throughout all bitou bush infestations although its num- It is also essential that revegetation of disturbed habi- bers are still increasing in some areas. In many areas, tat using native and preferably endemic species occurs it is having a significant impact on flowering and seed quickly to prevent the niche previously occupied by production of bitou bush. Experiments are currently bitou bush being colonised by bitou bush seedlings or under way to quantify the impact of C. germana. Pre- by another weed species. Because of the importance liminary results indicate populations in excess of 400 of revegetation there will always be a place for hand larvae/m2 can occur. High population levels have re- removal and rehabilitation work carried out by volun- duced seed production by over 50% at some sites. teer groups in areas of high conservation significance M. polana was first released in very low numbers in where other control techniques may not be suitable. August 1996 at Iluka Bluff and Dunbogan. Since then, Assuming approval is granted for the release of the nine releases have been made on the NSW North Coast. remaining biological control agents under investiga- By August 1998, M. polana had been found from near tion and that they subsequently establish, we believe Fraser Island in Queensland to Tathra in southern NSW, 668 Twelfth Australian Weeds Conference that by early in the new millennium we will have in Parsons, W.T. and Cuthbertson, E.G. (1992). ‘Noxious place an effective, complementary suite of insects, Weeds of Australia’. (Inkata Press, Melbourne). mites and pathogens for land managers to utilise as Scott, J.K. and Adair, R.J. (1990). The commencement part of an IWM program for bitou bush.
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