Target pest: Cirsium arvense (Asterales: Asteraceae), Californian thistle
Agent introduced: Cassida rubiginosa (Coleoptera: Chrysomelidae), green thistle beetle, thistle tortoise beetle
Import source: Switzerland
Release details: Gourlay (2010) - in November 2007 50 were released at Waitahuna West near Lawrence, Otago, 50 at Glenomaru near Owaka, South Otago, 50 at Caberfeigh, Catlins, South Otago and 50 in Hokonui Hills near Browns, Central Southland. Landcare Research (2015b) - earliest releases Southland/Otago, but now widely released throughout NZ, including 65 beetles near Masterton (Wairarapa) 2008 (with recently 30,000 collected and redistributed from this site) and 120 beetles Manawatu-Wanganui 2008 (with recently collections from this site distributed to 16 further sites in the region). Landcare Research (2015j) - 5 releases in 2014/2015.
Establishment: Landcare Research (2015b) - early reports suggest 90% establisment at original release sites, and good establishment at later releases in Wairarapa (where there has been a huge outbreak) and Manawatu-Wanganui.
Impacts on target: Landcare Research (2013f) - small beetle population at Lincoln, Canterbury caused striking damage in spring/summer 2012/13, eating all green leaf tissue on some plants by late-December. Landcare Research (2015b) - heavy defoliation of thistles in some regions, plants demolished in Wairarapa. Landcare Research (2018j) - since release in 2007 C. rubiginosa has been starting to make good progress towards reducing C. arvense populations in many areas. A trial underway in North Canterbury since 2015 indicates that 10 or more larvae per shoot are required to significantly reduce the density and spread of Californian thistle, with shoots incurring greater feeding damage less likely to become reproductive. The trial has also suggested that rainfall is an important factor in determining the level of damage to the thistle, with water-stressed plants more susceptible to the beetle. This might explain why C. rubiginosa has not performed well to date in the south where rainfall is higher.
Impacts on non-targets: Landcare Research (2013f) - damage at Lincoln observed on scotch thistle (Cirsium vulgare), though to a much lesser degree than on Californian thistle at the same site. Paynter et al. (2015) - surveys of potential non-target hosts Carduus nutans (nodding thistle), Cirsium vulgare (Scotch thistle) and Cynara scolymus (globe artichoke) show the former two (both exotic weeds) are 'full' hosts (can support breeding populations), and minor 'spillover' feeding on the latter. Paynter et al. (2017) - minor spillover feeding on Cynara scolymus was an anticipated risk considered acceptable by regulatory authorities when approval for release was granted. Hettiarachchi et al. (2018) - adult C. rubiginosa have been observed to feed and oviposit on field populations of nodding thistle, Scotch thistle, winged thistle (Carduus tenuiflorus), marsh thistle (Cirsium palustre), and artichoke. Utilisation of these plants was predicted by pre-release choice and no-choice host testing; however, the potential impact on individual plant, or population performance, is uncertain. A potted plant trial showed C. rubiginosa had minimal impact on the performance of marsh thistle. However, under field conditions, where plants are likely to encounter additional stressors, and with the opportunity to attack smaller rosettes, the beetle may be able to impact this thistle.
General comments: 10 Nov 2006 – application by the Californian Thistle Action Group (CalTAG) to import for release a weevil, Ceratapion onopordi (Brentidae) and a beetle, Cassida rubiginosa (Chrysomelidae), for the biological control of the weed Californian thistle (Cirsium arvense). EPA Application #NOR06005, approved without controls 2 Mar 2007.
Gourlay H (2010). Green Thistle Beetle. In The Biological Control of Weeds Book (Landcare Research) http://www.landcareresearch.co.nz/research/biocons/weeds/book/documents/Green_Thistle_Beetle.pdf
Hettiarachchi D, Cripps M, Jackman S, van Koten C, Sullivan J, Rostás M. (2018). Impact of the biocontrol beetle, Cassida rubiginosa, on the secondary weed target, marsh thistle (Cirsium palustre). New Zealand Plant Protection 71: 66-71
Landcare Research (2013f). Beetles decimate Californian thistles at Lincoln. What's new in biological control of weeds? 64: 4 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-64
Landcare Research (2015b). First major green thistle outbreak. What's new in biological control of weeds? 72: 4-5 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-72
Landcare Research (2015j). Biocontrol agents released in 2014/15. Weed Biocontrol: What's New? 73: 2 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-73
Landcare Research (2018j). How effective is the green thistle beetle? Weed Biocontrol: What's New? 86, November 2018.
Paynter Q, Fowler SV, Groenteman R. (2017). Making weed biological control predictable, safer and more effective: perspectives from New Zealand. BioControl (First online: 8 Aug 2017). https://doi.org/10.1007/s10526-017-9837-5
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