Biocontrol introduction
Target pest: Carduus nutans (Asterales: Asteraceae), nodding thistle
Agent introduced: Urophora solstitialis (Diptera: Tephritidae), nodding thistle gall fly
Imported:
1989, 1992
Import source:
1989 Austria, 1982 France via Australia
Import notes:
Groenteman (2011a) - because of difficulties rephasing the Austrian gall flies to Southern Hemisphere conditions, Landcare Research imported an additional French strain in 1992 from Australia.
Released:
Early-1990s
Release details:
Groenteman (2011a) - mass reared and released widely during the early-1990s.
Establishment:
Harman et al. (1996) - it is known to have established in Canterbury and Marlborough.
Groenteman (2011a) - established and becoming widespread in both the North and South Islands.
Landcare Research (2014c) - becoming common.
Impacts on target:
Groenteman (2007) - it has been estimated to destroy up to 27% seed produced but its impact may be lessened by Rhinocyllus conicus, which appears to out-compete it for oviposition sites, and by Trichosirocallus horridus, possibly as a result of reduced resource quality. However although its impact is lessened by T. horridus the two together have a greater impact that either individually.
Groenteman (2011a) - the impact of the gall fly has only been measured in Canterbury where it was only able to destroy about 8% of total seed production. The gall flies were being adversely affected by nodding thistle receptacle weevils early in the season, which was limiting their effectiveness later in the season. The impact of the gall fly in other parts of New Zealand is unknown but it is likely to vary from place to place and from year to year.
Landcare Research (2014c) - can help to provide control in conjunction with other thistle agents.
Paynter et al. (2018) - modelling indicates that U. solstitialis, along with the introduced biocontrol agent Trichosirocalus horridus, is responsible for partial control of nodding thistle, although predation of U. solstitialis larvae by larvae of the introduced biocontrol agent Rhinocyllus conicus reduces the efficacy of U. solstitialis.
Landcare Research (2022j) - biocontrol agents were introduced against C. nutans in 1972 (Rhinocyllus conicus), 1984 (Trichosirocalus horridus) and 1990 (Urophora solstitialis). Although there were widespread reports of declines in abundance of C. nutans several years after establishment of T. horridus in particular, the thistle seemed to remain a serious pasture weed in some parts of New Zealand, and quantitative, nationwide data have been absent. To provide such data, revisits between 2013 between 2021 were made to 118 release sites across New Zealand where there are good records of nodding thistle density within four years of the release of either T. horridus or U. solstitialis. Results show the average C. nutans density at sites within 3 years of releases (1988-98) was 3.1 plants per square metre, and that this had dropped to 0.65 plants per square metre (a 78.9% reduction) at the 2013-21 revisits. There are still some heavily infested nodding thistle sites, even after biocontrol; there was no apparent geographical variation in this pattern, and no obvious factors to explain it. While the 79.8% reduction in C. nutans density cannot definitively be linked to biocontrol, there has been no change to Californian thistle (Cirsium arvense) densities at these sites, suggesting nodding thistle density has reduced due to biocontrol rather than land management changes. Approximately half the land managers at the revisit sites now spray less (or not at all) for nodding thistle; if these control costs are being achieved on just 10% of New Zealand sheep and beef farms, then the current, ongoing national cost saving is $26 million per year, a huge benefit:cost ratio for the complete nodding thistle biocontrol programme of 580:1.
Fowler et al. (2023), Landcare Research (2023h) - a cost-benefit analysis of all weed biocontrol programmes in New Zealand showed that in 2022 investment in weed biocontrol in the productive sector (targeting agricultural as opposed to environment weeds) was NZ$0.69 million, with the three most economically successful weed biocontrol programmes in New Zealand - against ragwort (Jacobaea vulgaris), St John’s wort (Hypericum perforatum) and nodding thistle (Carduus nutans) - yielding a combined annual benefit of NZ$84.7 million.
Impacts on non-targets:
Paynter et al. (2004) - surveys of globe artichoke (Cynara scolymus), the only valued thistle in New Zealand, record no U. solstitialis feeding, as predicted by lab tests.
Groenteman (2011a) - the gall flies may attack other Carduus thistles [also weeds in New Zealand], but strongly prefer nodding (Carduus nutans) and plumeless thistle (C. acanthoides). Other plants are not thought to be at risk.
Cripps et al. (2020) - in Feb/Mar 2018, a survey of thistle seedhead-feeding biocontrol agents was undertaken in 18 pastures under sheep and/or beef production across the North and South Islands. Urophora solstitialis was not recorded on any thistle other than C. nutans. In Dec 2019 an opportunistic collection of thistle seedheads from three locations in the Gisborne region did not detect U. solstitialis on any thistles present (Cirsium arvense, Carduus tenuiflorus, Silybum marianum). Urophora solstitialis has not been recorded on any host plants other than Carduus nutans in New Zealand, although closely related Carduus species are within its host range.
References
Cripps M, Navukula J, Kaltenbach B, van Koten C, Casonato S, Gourlay H. (2020). Spill-over attack by the gall fly, Urophora stylata, on congeners of its target weed, Cirsium vulgare. New Zealand Plant Protection 73: 24–32 https://doi.org/10.30843/nzpp.2020.73.11718
Fowler SV, Groenteman R, Paynter Q (2023). The highs and the lows: a cost benefit analysis of classical weed biocontrol in New Zealand. BioControl (2023) https://doi.org/10.1007/s10526-023-10225-2
Groenteman R (2007). Multi-Species Interactions in Weed Biocontrol: Carduus nutans as a case study. PhD Thesis. Unversity of Canterbury, New Zealand
Groenteman R (2011a). Nodding Thistle Gall Fly. The Biological Control of Weeds Book (Landcare Research) https://www.landcareresearch.co.nz/__data/assets/pdf_file/0015/20508/nodding_thistle_gall_fly.pdf
Harman HM, Syrett P, Hill RL, Jessep CT. (1996). Arthropod introductions for biological control of weeds in New Zealand, 1929 - 1995. New Zealand Entomologist, 19(1): 71-80
Landcare Research (2007a). New Zealand Arthropod Collection (NZAC) Biological Control Voucher Collection. Landcare Research website [Updated 2020] https://www.landcareresearch.co.nz/tools-and-resources/collections/new-zealand-arthropod-collection-nzac/databases-and-holdings/new-t2-landing-page/
Landcare Research (2014c). Who's who in biocontrol of weeds? What's new in biological control of weeds? 69: 10-11 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/WhatsNew69.pdf
Landcare Research (2022j). Comparing nodding thistle then and now. Weed Biocontrol: What's New? 102, November 2022 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/comparing-nodding-thistle-then-and-now/
Landcare Research (2023h). The highs and lows of cost-benefit analyses. Weed Biocontrol: What's New? 106, August 2023 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/the-highs-and-lows-of-costbenefit-analyses/
Paynter Q, Fowler SV, Groenteman R. (2018). Making weed biological control predictable, safer and more effective: perspectives from New Zealand. BioControl 63: 427–436 (first published online 8 Aug 2017) https://doi.org/10.1007/s10526-017-9837-5 https://link.springer.com/article/10.1007/s10526-017-9837-5
Paynter QE, Fowler AH, Gourlay AH, Haines ML, Harman HM, Hona SR, Peterson PG, Smith LA, Wilson-Davey JRA, Winks CJ, Withers TM (2004). Safety in New Zealand weed biocontrol: A nationwide survey for impacts on non-target plants. New Zealand Plant Protection 57: 102-107 https://journal.nzpps.org/index.php/nzpp/issue/view/vol57
