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Biocontrol introduction

Target pest: Jacobaea vulgaris (Asterales: Asteraceae) = Senecio jacobaea, ragwort

Agent introduced: Platyptilia isodactyla (Lepidoptera: Pterophoridae), ragwort plume moth



Import source:

Europe via Australia

Import notes:

Hill (2005) - Platyptilia isodactyla will be imported into New Zealand as adults from a laboratory culture in Tasmania, Australia founded from insects collected at or near the same site as the populations used for recent host-range testing [see Hill (2005) entry in ‘Impacts on non-targets’ section below].

Gourlay (2011b) - Platyptilia isodactyla is native to Europe and was imported into New Zealand from Australia in 2005 by Landcare Research, in conjunction with the West Coast Ragwort Control Trust, because existing agents were not able to control ragwort in areas of higher rainfall. The plume moth is commonly found on marsh ragwort (Jacobaea aquatica) and therefore is well adapted to wet climates and expected to be well suited to areas like the West Coast of the South Island.



Release details:

Hayes (2007a) - released at a limited number of sites nationwide since autumn 2006.

Landcare Research (2013d) - released at 47 sites on the West Coast (where the ragwort flea beetle, Longitarsus jacobeaea, is ineffective due to high rainfall) and releases here are continuing.


Gourlay (2011b) - appears to be establishing readily.

Landcare Research (2013d) - established at around 85% of West Coast release sites.

Landcare Research (2014c) - well established.

Landcare Research (2016h) - over 70 L. jacobaeae (ragwort flea beetle) release sites nationwide revisited 20-30 years post-release and density of ragwort now compared to density at the time of release: the plume moth was present at 7 sites; on the West Coast the plume moth has self-colonised at least three of the flea beetle release sites, including the wettest site in the study (Whataroa, with a mean annual rainfall of 5,305 mm).

Gourlay (2021d) - Platyptilia isodactyla is now well established in much of New Zealand.

Impacts on target:

Gourlay (2011b) - Platyptilia isodactyla is reducing ragwort as was hoped.

Landcare Research (2013d) - some release sites have been active for seven years and are showing a significant reduction in ragwort populations, such that farmers only have to spot spray instead of boom or helicopter spraying. Good results with plume moth also reported in other parts of New Zealand.

Landcare Research (2014c) - quickly reducing ragwort noticeably at many sites.

Landcare Research (2016g) - three to five years after release ragwort populations started disappearing. Between the plume moth and the flea beetle (Longitarsus jacobeaea), which is effective in drier areas, almost throughout New Zealand ragwort has become relatively rare.

Landcare Research (2016h) - study of ragwort flea beetle release sites: data showed the plume moth may already be causing some declines in ragwort at wet sites on the West Coast, supporting other observations of the impact of this agent.

Gourlay (2021d) - there have been no studies to determine the effect of P. isodactyla on ragwort populations in New Zealand. However, a reduction in ragwort at release sites has been commonly observed within a few years of the moth’s release. The plume moth, the flea beetle Longitarsus jacobeaea [also released against ragwort] and ragwort have all become a relatively rare in much of New Zealand now due to their impact of these biocontrol agents.

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.

Paynter (2024) - factors influencing the success of weed biocontrol agents released and established in New Zealand were investigated. Each agent’s impact on the target weed in New Zealand was assessed as ‘heavy’, ‘medium’, ‘variable’, ‘slight’ or ‘none’, where a ‘heavy’, ‘medium’ or ‘variable’ impact have all been observed to reduce populations or percentage cover of their target weed in all or part of their respective target weed ranges in New Zealand. Results showed that: (i) agents that are highly damaging in their native range were almost invariably highly damaging in New Zealand; (ii) invertebrate agents with a closely related ‘native analogue’ species are susceptible to parasitism by the parasitoids that attack their native analogues and failed to have an impact on the target weed, and (iii) agent feeding guild helped predict agent impact - in particular, agents that only attack reproductive parts of the plant (e.g., seed and flower-feeders) are unlikely to reduce weed populations. Damaging impacts of P. isodactyla, a crown-boring moth, have been reported in its native range, it does have not a New Zealand native ecological analogue and its impact in New Zealand is assessed as ‘variable’.

Impacts on non-targets:

Hill (2005) - studies on the potential host range of P. isodactyla include field surveys and laboratory trials in Europe and Australia and host-range tests with New Zealand native plants in containment in New Zealand. In total, 63 plant taxa were tested, including 34 species in the tribe Senecionaeae, of which 12 were New Zealand natives. In New Zealand trials, larvae failed to complete development on any non-host plants except the European species Jacobaea maritima [syn Senecio cineraria - dusty miller], a garden species that is naturalised and spreading in New Zealand. In Australian laboratory trials, occasional larvae completed development on J. maritima and a European weed species as well as two native Australian species, although development success never exceeded 7% of larvae. However, P. isodactyla was not found in field surveys in Australia that sampled native plants closely related to J. vulgaris (although this agent was only released in Australia 5-6 years prior to the surveys, so it may be too soon to be certain it will not colonise Australian natives, some of which are also native to New Zealand). These trials and surveys support the view that P. isodactyla will not be able to colonise non-target plants in New Zealand, although occasional eggs may be laid on a limited number of non-target species, on which larvae may feed briefly, and occasional adults may emerge from Jacobaea maritima. [NB: the host-range testing described here did not test Jacobaea aquaticus, a known host and minor weed in New Zealand - see Gourlay (2011b) entries in this section and ‘Import notes’ section above.]

Gourlay (2011b) - extremely unlikely P. isodactyla will damage plants other than ragwort and marsh ragwort, Jacobaea aquaticus (syn Senecio aquaticus), which is also a minor weed in New Zealand, and hybrids of the two species.

Paynter et al. (2015) - surveys of potential non-target host the exotic ornamental Jacobaea maritima (syn Senecio cineraria) (dusty miller) report no feeding.

General comments:

Taxonomic note (29 June 2024) - at the time that P. isodactyla was introduced into New Zealand, ragwort, the target weed, was classified as Senecio jacobaea. However, molecular studies of the tribe Senecioneae by Pelser et al. (2006) showed that species of Senecio sect. Jacobaea (Mill.) Dumort. formed a well-supported clade that is only distantly related to other species usually attributed to Senecio, and proposed transferring the 27 species of sect. Jacobaea they analysed to the genus Jacobaea Mill. This included Senecio jacobaea, reclassified as Jacobaea vulgaris.

EPA Applications:

EPA (2005b) - 1 Jul 2005: application by West Coast Ragwort Control Trust to import for release two new moths, Cochylis atricapitana (Tortricidae) and Platyptilia isodactyla (Pterophoridae), for the biological control of the pasture weed ragwort. EPA Application # NOR05002, approved without controls 15 Dec 2005.


EPA (2005b). EPA application NOR05002 to import for release two new moths, Cochylis atricapitana (Tortricidae) and Platyptilia isodactyla (Pterophoridae), for the biological control of the pasture weed ragwort. Environmental Protection Authority website https://www.epa.govt.nz/database-search/hsno-application-register/view/NOR05002

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

Gourlay H (2011b). Ragwort plume moth: Platyptilia isodactyla. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Updated 2021 - see Gourlay (2021d)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/ragwort-plume-moth/

Gourlay H (2021d). Ragwort plume moth: Platyptilia isodactyla. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Update of Gourlay (2011b)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/ragwort-plume-moth/

Hayes L (2007a). Status of weed biocontrol agents in Southland. A report prepared for Environment Southland Sept 2007. Landcare Research Contract Report: LC0708/022

Hill RL (2005). Application to EPA (NOR05002) to import for release, or release from containment, new organisms, Cochylis atricapitana and Platyptilia isodactyla. Environmental Protection Authority website https://www.epa.govt.nz/assets/FileAPI/hsno-ar/NOR05002/1097089c99/NOR05002.pdf

Landcare Research (2013d). West Coast ragwort control - a successful community project. What's new in biological control of weeds? 66: 2-3 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-66

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 (2016g). Farmer grateful for tiny beetle. Weed Biocontrol: What's New? 76: 8 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-76

Landcare Research (2023h). The highs and lows of cost-benefit analyses. Weed Biocontrol: What's New? 106, November 2023 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/the-highs-and-lows-of-costbenefit-analyses/

Paynter Q (2024). Prioritizing candidate agents for the biological control of weeds. Biological Control, Volume 188, January 2024, Article Number 105396 https://doi.org/10.1016/j.biocontrol.2023.105396

Paynter QE, Fowler SV, Gourlay AH, Peterson PG, Smith LA and Winks CJ (2015). Relative performance on test and target plants in laboratory tests predicts the risk of non-target attack in the field for arthropod weed biocontrol agents. Biological Control 80: 133-142 https://doi.org/10.1016/j.biocontrol.2014.10.007

Pelser PB, Veldkamp J-F, Van der Meijden R (2006). New combinations in Jacobaea Mill. (Asteraceae – Senecioneae). Compositae Newsletter 44: 1-11 https://www.researchgate.net/publication/247158930_New_combinations_in_Jacobaea_Mill_Asteraceae-Senecioneae