Paterson's Curse, Onopordum and Nodding Thistles
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Thirteenth Australian Weeds Conference Biological control of broad-leafed pasture weeds ( Paterson’s curse, Onopordum and nodding thistles) What have we achieved and where to from here? Anthony Swirepik and Matthew Smyth CRC for Australian Weed Management and CSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia Summary Since 1996 the Australian Wool Innova- establishment and initial spread, level two provides tion (AWI) and Meat and Livestock Australia (MLA) data on plant density and attack rate, and level one have funded a national biocontrol agent redistribution provides detailed data on the impact of agents on project. Through this process, 17 insects have been seed production and seed bank dynamics (see Briese released on three weeds and six are impacting on the et al 1998). Data collected provide information that fi tness of their host. As a result, Carduus nutans has supports management decisions for the future priori- been controlled at study sites in the Southern Table- ties of the project, as well as providing feed back to lands of NSW, Onopordum spp. seed production is everyone from landholders to funding partners on the being reduced by greater than 80% at several sites and progress of the project. plant mortality of Echium plantagineum is recorded at several sites. A recent economic analysis (Nordblom Achievements to date During the life of the broad et al. 2000) has shown that redistribution needs to leaf pasture weed biological control projects, 17 spe- continue to maximise the potential of these insects cies of agent have been released against the three across the entire range of the weeds. target weeds (Briese et al 2002, Sheppard et al. 1999, Keywords Biological control, Onopordum, Carduus, Woodburn 1997, Woodburn and Cullen 1995, Wood- Echium, redistribution, monitoring, impact. burn 1993). Of these 17 species, three agents were established prior to the inception of the redistribution INTRODUCTION project and were not included in it. They are the Pater- CSIRO Entomology initiated biological control son’s curse leaf-mining moth (Dialectica scalariella) projects against the broad-leafed pasture weeds and the stem boring weevil (Phytoecia coerulescens) Echium plantagineum (Paterson’s curse), Onopordum and the nodding thistle seed weevil (Rhinocyllus illyricum / O. acanthium ( Scotch and Illyrian thistle) conicus). The leaf miner was the fi rst agent released and Carduus nutans (nodding thistle) in the late on Paterson’s curse in Australia, this agent quickly 1980s. Up until 1996/1997, Australian Wool Innova- became established across the range of its host, and tion (AWI) and Meat and Livestock Australia (MLA) was therefore not considered for redistribution. In the funded the three projects independently, with the work case of the stem borer, a post-release impact study was focusing mostly on the importation, host-specifi city carried out which indicated that it would have little testing and initial establishment of agents at a small impact of Paterson’s curse (Smyth and Sheppard 2000). number of nursery sites. From 1997/1998, the three A decision was therefore made not to redistribute it projects were placed under one funding umbrella with away from initial sites. a fourth project on the biocontrol of Cirsium thistles Releases of the nodding thistle seed weevil (R. (run by DNRE, Victoria). The project focuses on the conicus) were completed prior to the advent of the establishment, redistribution and monitoring of agents current project (Woodburn and Cullen 1995). The across temperate Australia, with the main objective seed weevil has dispersed naturally across the range being the fast tracking of the delivery of biocontrol of nodding thistle from a limited number of initial to the end user. The process involves offi cers from release sites in the three main regions of infestation, CSIRO Entomology, State departments of Agriculture, the Monaro, Central/Southern and the New England local government and Landcare, who work to engage tablelands. members of the community in the release and redistri- Table 1 lists the 12 agents that the project has bution process, with the aim of handing over the fi nal focused on since 1997/1998. Of these, ten are estab- responsibility for local redistribution to them. lished in the fi eld, while it is too early to confi rm the Monitoring of agent performance is carried out establishment of the Onopordum rosette fl y (Botano- parallel to the release process. Monitoring has been phila spinosa) and seed fl y (Urophora terebrans). The developed around a three tiered structure, where number of species established is high compared to the level three monitoring provides data on broad scale average establishment rate of 60–70% for biocontrol 373 Thirteenth Australian Weeds Conference programs globally (Syrett et al. 2000). This refl ects the Onopordum thistles Level two monitoring of the value of funding the development of effective release performance of the Onopordum seed weevil (Larinus and redistribution strategies. latus) indicates that local population densities at older Two species have failed to establish; the fi rst release sites have now reached levels that are signifi - species of seed fl y (Tephritis postica) released on cantly suppressing seed production (Figure 3) and Onopordum thistles, and a second species of fl ea that this suppression is increasing with time. If these beetle (Longitarsus aeneus) released on Paterson’s trends continue a reduction in the soil seed bank will curse. Failure of the seed fl y to establish has been at- result. Another positive indication of the performance tributed to the inability of the species to overcome the of the seed weevil is that populations are routinely effects of small initial release numbers or Allee effect being found at isolated sites tens of kilometres from (Hopper and Roush 1993) associated with releasing a the nearest release. new species. Failure of the fl ea beetle to establish has been attributed to our inability to resynchronise the species to southern hemisphere seasons. Table 1. Agents released against the three broad- A GLIMPSE OF SOME MONITORING DATA leafed pasture weeds in Australia. Nodding thistle The release and redistribution phase of the nodding thistle project has come to a conclusion Weed Agent Species No. of releases during the past three years. However, the monitoring of the performance of the agents and their host plant has Onopordum Larinus latus 227 continued. Figure 1 illustrates that the mean Carduus Lixus cardui 549 seed bank at Yaouk and Kybeyan have declined from Eublemma amoena** 40 a high of 9500 seeds m-2 in 1989 to 397 seeds m-2 in Trichosirocalus briesii*3 2001 (P<0.0001), a density that is comparable with Botanophila spinosa*2 European seed banks (Sheppard et al. 1988). Figure 1 Urophora terebrans*1 also shows how plant densities varied over 1989–1995 C. nutans Urophora solstitialis 101 compared to the last four years 1998–2001; these dif- Trichosirocalus horridus 102 ferences are signifi cant (P<0.001). Figure 2 further E. plantagineum Mogulones larvatus** 1124 supports the hypothesis that seed banks are being Mogulones geographicus*95 depleted at monitoring sites. Longitarsus echii* 103 Plant densities have signifi cantly declined since Meligethes planiusculus*53 1998 (P<0.05), while T. horridus attack by June has *Agents requiring further regional and local redistribution steadily increased to 60% of plants. At this attack rate, effort after April 2002. for the similar crown weevil for Paterson’s curse, plant ** Agents requiring only further local redistribution effort mortally has reached 100% (Sheppard et al. 1999). after April 2002. 200 10000 180 9000 Plant density 160 8000 Seed Bank 140 7000 -2 -2 120 6000 100 5000 80 4000 Seeds m 60 3000 Plant density m 40 2000 20 1000 0 0 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 Year Figure 1. The Carduus soil seed bank and plant density at Yaouk and Kybeyan 1988–2000. 374 Thirteenth Australian Weeds Conference Paterson’s curse Figure 4 shows the mean plant that attack rate in high rainfall regions will increase densities and crown weevil (Mogulones larvatus) at- with time, to the point where impact is detectable by tack rates (AR) from 30 level two sites sampled across the monitoring protocol. In contrast, the attack rate Australia from 1997–2001. Highest AR (% of attacked of M. larvatus in late break Mediterranean regions plants) has been included to illustrate the full range of (particularly WA) has remained below 10%. The late results being achieved at level 2 sites. The overall trend break to the season (May–June) in these regions and is that crown weevil attack rates across Australia are the ability of the weevil to only aestivate successfully on the increase, although there are still a number of until April explains the difference in weevil attack sites where little or no attack is being detected by the rates. In contrast the fl ea beetle, Longitarsus echii has monitoring protocol. The weevils have established at established at 84% of sites so far and is well suited to these sites with low attack rates and it is anticipated the climate in WA (Smyth and Sheppard 2002). DISCUSSION Plants m-2 % attacked Where to from here? There will be a need for ongo- 80 100 ing redistribution effort of agents for both Onopordum 80 (four agents, see Table 1) and Paterson’s curse (four -2 60 60 agents, see Table 1) so that the maximum benefi t of 40 the full biocontrol suite may be realised across the 40 Plants m distribution of the target weeds. 20 20 % rosettes attacked 0 0 How do we know when we’ve made enough releases? 1998 1999 2000 2001 The Onopordum stem-boring weevil (Lixus cardui) Year is one of two agents for which the regional and local Figure 2.