Biocontrol introduction
Target pest: Hieracium spp. (Asterales: Asteraceae), hawkweed
Agent introduced: Aulacidea subterminalis (Hymenoptera: Cynipidae), hieracium gall wasp
Imported:
1997, 1998, 1999
Import source:
Germany, 1997 1998; Switzerland, 1999
Released:
1999
Release details:
Smith (2007) - lmported in 1997, widespread releases began in 1999.
Establishment:
Smith (2007) - established but not widespread at sites in the North and South Islands. Landcare Research (2014c) - established but not yet common in the South Island and has not established yet in the North Island. Paynter et al. (2018) - abundant at some release sites.
Landcare Research (2020e) - surveys in 2020 at release sites - Canterbury and Otago in the South Island (Marlborough release sites were not visited) and on the Central Plateau of the North Island - showed A. subterminalis has established in both the North and the South Islands, although establishment rate and efficacy differ between the two. In the South Island, gall wasps were recovered from 92% of the release sites and had dispersed widely (away from the original release sites), while in the North Island, they were only recovered from 15% of sites and evidence of their dispersal was limited.
Impacts on target:
Landcare Research (2014c) - impact unknown but reduces stolon length in lab trials.
Landcare Research (2020e) - 2020 surveys showed that despite the widespread distribution of A. subterminalis, only 4.5% of hieracium plants at South Island sites where the wasp was present were galled by the wasp. In a 2006 study less than 1% had been galled by the wasp. Although site comparisons over time show that hieracium densities have been reduced by 10% in the South Island, this is predominantly attributed to changes in land management practices, such as irrigation, cultivation and reduced grazing pressure, rather than biocontrol.
Landcare Research (2020g) - appears to be having minimal impact.
Landcare Research (2021d) - the lack of impact by the gall wasp in the South Island appears to be due to a lack of stolons at the drier, more exposed hieracium sites. Although an average of 67% of stolons are galled by the wasp, only 7% of hieracium plants growing in these environments have stolons, which would severely limit establishment and population growth of the wasp.
References
Landcare Research (2007a). New Zealand Arthropod Collection (NZAC) Biological Control Voucher Collection. http://www.landcareresearch.co.nz/resources/collections/nzac/holdings/biological-control-voucher-collection
Landcare Research (2020e). Hieracium biocontrol – 20 years on. Weed Biocontrol: What's New? 93, Aug 2020 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/hieracium-biocontrol-20-years-on/
Landcare Research (2020g). Who's who in biological control of weeds? Weed Biocontrol: What's New? 93, Aug 2020. https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/status-of-agents/
Landcare Research (2021d). Hieracium biocontrol: where to from here? Weed Biocontrol: What's New? 96, May 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/hieracium-biocontrol-where-to-from-here/
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
Smith L (2007). Hieracium Gall Wasp. In The Biological Control of Weeds Book (Landcare Research) http://www.landcareresearch.co.nz/research/biocons/weeds/book/documents/Hieracium_Gall_wasp.pdf
