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Biocontrol introduction

Target pest: Hawkweeds (Pilosella, Hieracium spp.) (Asterales: Asteraceae)

Agent introduced: Cheilosia psilophthalma (Diptera: Syrphidae), hieracium root hover fly


Late 1990s, early-to-mid-2000s

Import source:


Import notes:

Landcare Research (2006d) - further shipments of both Cheilosia urbana and C. psilophthalma have been received this year by Landcare Research from Commonwealth Agricultural Bureaux International (CABI), Switzerland, but very few adults emerged. Neither CABI nor Landcare Research have been able to establish a breeding population and CABI is only able to send larvae from mated females collected in the field.

Smith (2007a) - several shipments were imported into New Zealand from Switzerland by Landcare Research, in conjunction with the Hieracium Control Trust, in the late 1990s for host range testing. Following permission in 2001 to release the hover flies a further shipment was imported to begin a rearing colony.

Landcare Research (2007a) - specimens of C. psilophthalma from Switzerland, dated 1998, are present in the Biological Control Voucher Collection of the New Zealand Arthropod Collection [indicating an importation from that source in that year].

Released: 2006

Release details:

Landcare Research (2006d) - the first, albeit rather small, release of C. psilophthalma in New Zealand has been made, of adults emerging from a shipment of larvae from Switzerland.

Landcare Research (2008) - only one release of C. psilophthalma has been made so far; rearing difficulties need to be overcome to allow widespread releases to begin.


Landcare Research (2008) - establishment success, from the single release made so far, is unknown.

Landcare Research (2014c) - establishment success unknown.

Landcare Research (2020e) - surveys in 2020 at release sites of hawkweed biocontrol agents - Canterbury and Otago in the South Island (Marlborough release sites were not visited) and on the Central Plateau of the North Island [NB: C. psilophthalma was not necessarily released at all these sites] - did not recover any C. psilophthalma and it is presumed to have failed to establish, which is not surprising given the small numbers released.

Impacts on non-targets:

Hieracium Control Trust (2000) - host range tests were completed on 66 test plant species comprising 9 species from the genus Hieracium, 29 species in the family Asteraceae, including the closest relatives to Hieracium among native New Zealand plants, and 28 species from an additional 25 families of plants. Oviposition and larval development tests were carried out in Switzerland, or under insect containment conditions in New Zealand for those plants that could not be grown in Switzerland. No eggs were laid on plants other than Hieracium species, and no larvae survived on any plants other than Hieracium species. There are no native plants in the genus Hieracium; the genus is represented in New Zealand by weedy species introduced from Europe. The host range tests indicate the likelihood that any non-target species will be negatively affected is very low. [Note that subsequent to this publication, the genus Hieracium has been split into Hieracium and Pilosella - see Taxonomic note (17 February 2024) in 'General comments' section' - and species in both genera may be hosts for C. psilophthalma - seeTarget species note (17 February 2024) in 'General comments' section.]

Smith (2007a) - it is extremely unlikely that C. psilophthalma will attack plants other than mouse-ear hawkweed (Pilosella officinarum), king devil hawkweed (P. praealta), field hawkeed (P. caespitosa), tussock hawkweed (Hieracium lepidulum), and orange hawkweed (P. aurantiaca) [i.e. the four main target weeds - see Target species note (17 February 2024) entry in 'General comments' section - plus P. aurantiaca, another introduced weed].

General comments:

Target species note (17 February 2024) - in the 1990s and 2000s, six biocontrol agents were introduced to New Zealand to control hawkweeds, specifically four weedy species that at the time were considered to be in the genus Hieracium (with three of those in the subgenus Pilosella). Subsequently, Pilosella has been recognised as a distinct genus [see Taxonomic note (17 February 2024) entry below]; the four weed species are now classified as Pilosella officinarum (syn Hieracium pilosella) (mouse-ear hawkweed), P. caespitosa (syn H. caespitosum) (field hawkweed), P. praealta (syn H. praealtum) (king devil hawkweed) and H. lepidulum (tussock hawkweed). Of the biocontrol agents, the rust Puccinia hieracia var. piloselloidarum and the gall wasp Aulacidea subterminalis attack only P. officinarum, the plume moth Oxyptilus pilosellae attacks both P. officinarum and P. caespitosa, the gall fly Macrolabis pilosellae attacks all three Pilosella species, and the hover flies Cheilosia urbana and C. psilophthalma attack all four hawkweed species. (Information from Hieracium Control Trust (2000).)

Taxonomic note (17 February 2024) - at the time that C. psilophthalma was introduced to New Zealand, the target weeds (hawkweeds) were all considered to be in the genus Hieracium. Bräutigam & Greuter (2007) note that Pilosella was considered by many authors to be a subgenus of Hieracium but that in recent decades generic recognition of Pilosella had gained increased support. Bräutigam & Greuter (2007) recognise Pilosella as a distinct genus from Hieracium and reclassify the Euro-Mediterranean flora accordingly. Under this classification there are introduced hawkweeds present in New Zealand in both genera (Hieracium and Pilosella) [see Target species note (17 February 2024) entry above].

EPA Applications:

EPA (2001) - 17 Nov 2000: application by the Hieracium Control Trust to import for release the insects Macrolabis pilosellae (Binnie 1878), Cheilosia urbana (Meigen 1822) and Cheilosia psilophthalma (Becker 1894) for the purpose of biological control of hawkweeds, Hieracium spp. EPA Application #NOR00001, approved without controls 27 Jun 2001.


Auckland Regional Council (). The Land 99 http://greensite.arc.govt.nz/library/:70039-2.pdf

Bräutigam S, Greuter W (2007). A new treatment of Pilosella for the Euro-Mediterranean flora. Willdenowia 37: 123-137 https://doi.org/10.3372/wi.37.37106

EPA (2001). EPA application NOR00001: to import for release the insects Macrolabis pilosellae (Binnie 1878), Cheilosia urbana Meigen and Cheilosia psilophthalma (Becker 1894) for the purpose of biological control of hawkweeds, Hieracium spp. Environmental Protection Authority website https://www.epa.govt.nz/database-search/hsno-application-register/view/NOR00001

Hieracium Control Trust (2000). Application to EPA (NOR00001) to import for release the insects Macrolabis pilosellae (Binnie 1878), Cheilosia urbana Meigen and Cheilosia psilophthalma (Becker 1894) for the purpose of biological control of hawkweeds, Hieracium spp. Environmental Protection Authority website https://www.epa.govt.nz/assets/FileAPI/hsno-ar/NOR00001/6b046d0b38/Application-NOR00001.pdf

Landcare Research (2006d). Hieracium heroes and heartbreakers. What’s New In Biological Control of Weeds? August 2006, 38: 8 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/wtsnew38.pdf

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 (2008). Who’s who in biological control of weeds. What’s New In Biological Control of Weeds? August 2008, 45: 14-15 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/wtsnew45.pdf

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 (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/

Smith L (2007a). Hieracium hover flies: Cheilosia urbana and ,i>Cheilosia psilophthalma. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Updated 2021] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/hieracium-hover/