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Biocontrol introduction

Target pest: Equisetum arvense (Equisetales: Equisetaceae), field horsetail

Agent introduced: Grypus equiseti (Coleoptera: Curculionidae), horsetail weevil


2013, 2017

Import source:

Landcare Research (2017a) - 2017 import from UK



Release details:

Landcare Research (2016i) - first field release planned for spring 2016.

Landcare Research (2017a) - the weevil has proved difficult to rear in containment; another importation from UK has just been received (May 2017) with the aim to build up the population so the first field release can be made in spring 2017.

Landcare Research (2018a) - in early-November 2017 the first adult horsetail weevils were released at two sites near Bulls in the Manawatu (lower North Island). Further releases were made in late-December at the first site on the edge of a wetland on a Parewanui dairy farm, and in January 2018 at the nearby second site along a fenced riparian strip. At both sites releases were made onto one of a paired set of plots, to enable the assessment of impacts as the weevils become established.

Landcare Research (2018h, 2019j) - 7 releases made in the year Sep 2017 - Aug 2018, 2 in the year Sep 2018 - Aug 2019.

Landcare Research (2020d) - as a result of rearing difficulties, only 545 weevils have been released since 2017. A new rearing system is being trailed with the hope that large releases of adult weevils can be made this coming (2020) spring.

Landcare Research (2021e) - 7 releases made in the year Sep 2020 - Aug 2021.

Landcare Research (2021g) - since approval to release the field horsetail weevil in 2017 it has been a struggle to establish field populations, probably due low numbers available for release. Following the success of a new rearing technique in 2020, 2,670 weevils have now been released; over 80% of these since rearing methods were improved. Releases have been made at six sites, all in Rangitikei District of the lower North Island. Assessment plots have been set up at five of these sites so impacts of the weevil on the target weed can be evaluated.

Landcare Research (2022h, 2023f) - six releases made in the year Sep 2021 - Aug 2022, six in the year Sep 2022 - Aug 2023.


Landcare Research (2020d) - establishment has yet to be confirmed. To date, no weevils have been recovered from the field, although the release sites have not been visited this year.

Landcare Research (2021f) - establishment is looking likely.

Landcare Research (2021g) - since the increase in number of beetles released (due to improved rearing methods in 2020) weevil damage has been recorded at three of the six release sites, strongly suggesting the weevils have established there.

Impacts on non-targets:

Landcare Research (2015k) - there are no New Zealand native genera in the same class as Equisetum; the most closely related native plants are currently believed to be the Marattioid ferns. Due to the extreme taxonomic isolation of E. arvense from native or valued exotics, a short test plant list was adequate to demonstrate environmental safety. Larval development tests confirmed that New Zealand test plant species are not hosts of G. equiseti and that it is unable to form populations on native New Zealand ferns and even minor spill-over attack is highly unlikely.

Smith (2016) - in its native range the horsetail weevil attacks a range of horsetail species and host-range testing has indicated that the other horsetail species also present in New Zealand, Equisetum hymale, is also a potential host.

EPA Applications:

EPA (2016b) - 20 Jan 2016: application by the Rangitikei Horsetail Group to introduce Grypus equiseti, a weevil for the control of field horsetail (Equisetum arvense). EPA Application # APP202712, approved without controls 19 May 2016.


EPA (2016b). EPA application APP202712: to introduce Grypus equiseti, a weevil for the control of field horsetail (Equisetum arvense). Environmental Protection Authority website https://www.epa.govt.nz/database-search/hsno-application-register/view/APP202712

Landcare Research (2015k). The host-range of Grypus equiseti (F.) (Erirhinidae), a potential control agent for field horsetail Equisetum arvense L. Landcare Research website. https://www.landcareresearch.co.nz/__data/assets/pdf_file/0017/107504/host_range_tests_Grypus_equiseti.pdf

Landcare Research (2016i). Who's who in biological control of weeds? Weed Biocontrol: What's New? 77: 10-11 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-77

Landcare Research (2017a). Three successes with Sustainable Farming Fund Weed Biocontrol: What's New? 80: 2 http://www.landcareresearch.co.nz/__data/assets/pdf_file/0013/141133/Issue-80.pdf

Landcare Research (2018a). First release of new agents. Weed Biocontrol: What's New? 83, February 2018 https://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-83/first-release-of-new-agents

Landcare Research (2018h). Biocontrol agents released in 2017/18. Weed Biocontrol: What's New? 85, August 2018 https://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-85/biocontrol-agents-released-in-201718

Landcare Research (2019j). Biocontrol agents released in 2018/19. Weed Biocontrol: What's New? 89, August 2019 https://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/weed-biocontrol-issue-89/biocontrol-agents-released-in-201819

Landcare Research (2020d). Clearing a hurdle for field horsetail weevils. Weed Biocontrol: What's New? 92, May 2020. https://www.landcareresearch.co.nz/news/clearing-a-hurdle-for-field-horsetail-weevils/

Landcare Research (2021e). Further reading and agents released. Weed Biocontrol: What's New? 97, August 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/further-reading

Landcare Research (2021f). Who's who in biological control of weeds? Weed Biocontrol: What's New? 97, August 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/whos-who-in-biological-control-of-weeds

Landcare Research (2021g). It is a numbers game for the field horsetail weevil. Weed Biocontrol: What's New? 98, November 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/it-is-a-numbers-game-for-the-field-horsetail-weevil/

Landcare Research (2022h). Further reading and agents released 2021/22. Weed Biocontrol: What's New? 101, August 2022 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/further-reading-and-agents-released-202122/

Landcare Research (2023f). Further reading and biocontrol agents released in 2022/23. Weed Biocontrol: What's New? 105, August 2023. https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/further-reading-and-agents-released

Smith L (2016). Field horsetail weevil: Grypus equiseti The biological control of weeds handbook (Landcare Research). http://www.landcareresearch.co.nz/__data/assets/pdf_file/0004/124708/Field-horsetail-weevil.pdf