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Biocontrol introduction

Target pest: Cytisus scoparius (Fabales: Fabaceae), Scotch broom, broom

Agent introduced: Aceria genistae (Acarina: Eriophyidae), broom gall mite

Imported: Self introduced and 2006

Import source: 2006 France

Released: 2006

Release details: Strains attacking Cytisus scoparius from France and UK were released in Canterbury in November 2007. Landcare Research (2014c) - 100 releases 2013/2014. Landcare Research (2015j) - 81 releases 2014/2015. Landcare Research (2016a) - 1,382 infested broom stems dropped by helicopter onto broom over a 30km stretch of the Clarence River bed (Canterbury) in 2015. Strategic releases have been made in North Canterbury and Kaikoura since 2012. Landcare Research (2018h) - 20 releases made in the year Sep 2017 - Aug 2018.

Establishment: Recovered at one site in Canterbury by November 2008. Landcare Research (2014c) - establishing well. Landcare Research (2016a) - while proving slow to establish in some regions the mite is booming in others, such as Canterbury. It is being more readily dispersed by wind than anticipated. Landcare Research (2017g) - establishing well and becoming widespread in some regions.

Impacts on target: Landcare Research (2014c) - severely damaging plants at some sites. Landcare Research (2015f) - very heavy galling observed at some sites e.g. Hanmer Springs. Landcare Research (2016a) - at Leslie Hills (North Canterbury) half of 144 marked broom plants killed by mite after 3 years, with the surviving plants galled. At Lincoln, Canterbury, 70 of 72 trial plants dead, most likely due to gall mite attack. At Waiau River (North Canterbury) significant damage, with large areas of broom killed, 3km downstream from 2009 release. Landcare Research (2017g) - showing considerable promise by beginning to cause extensive damage to broom at many sites. Paynter et al. (2017) - A. genistae an incipient success. Despite being preyed on by native and introduced predatory mites (mainly Typhlodromus caudiglan and Zetzellia maori), extremely damaging outbreaks have endured in New Zealand, perhaps because A. genistae mites are smaller than their phytoseiid predators so that there is a refuge from predation within the highly convoluted gall-like leaf curls. Landcare Research (2018c) - observations, and reports of, heavily galled Scotch broom plants dying.

Impacts on non-targets: Landcare Research (2018c) - host range testing undertaken before A. genistae was introduced into New Zealand in 2006 showed convincingly that it does not attack native broom and is unable to complete its life cycle without access to Scotch broom. Spill-over damage can sometimes occur on the close relative, tree lucerne (Cytisus proliferus), if broom gall mites are present in big numbers nearby, though they are not able to persist solely on this host.

General comments: Application to introduce this species to New Zealand was made under EPA application code NOR05003. As this nominal species was already present on Ulex europaeus, EPA determined that this was not an organism new to New Zealand.

References

Gourlay H (2010). Broom Gall Mite. In The Biological Control of Weeds Book (Landcare Research) http://www.landcareresearch.co.nz/research/biocons/weeds/book/documents/Broom_Gall_Mite.pdf

Gourlay, H (2009). The biological control of broom (Cytisus scoparius) IUFRO International Forest Biosecurity Conference, 16-20 March 2009, Rotorua, New Zealand. Popular Summaries. Compiled by Richardson M, Hodgson C and Forbes A. New Zealand Forest Research Institute Limited. 230-232

Landcare Research (2014c). Who's who in biocontrol of weeds? What's new in biological control of weeds? 69: 10-11 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-69

Landcare Research (2015f). Autumn activities. What's new in biological control of weeds? 71: 8 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-71

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 (2016a). Broom gall mite a decade on. Weed Biocontrol: What's New? 75: 3 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-75

Landcare Research (2017g). Who's who in biological control of weeds? Weed Biocontrol: What's New? 81: 10-11

Landcare Research (2018c). Galls on native broom no cause for concern. Weed Biocontrol: What's New? 84, May 2018

Landcare Research (2018h). Biocontrol agents released in 2017/18. Weed Biocontrol: What's New? 85, August 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