Target pest: Cirsium vulgare (Asterales: Asteraceae), Scotch thistle
Agent introduced: Urophora stylata (Diptera: Tephritidae), Scotch thistle gall fly
1997, 1999 Australia; 1999 Oregon USA
Hayes (2007d) - released at a limited number of sites in the late 1990s.
Hayes (2007d) - established readily.
Landcare Research (2014c) - established and spreading readily.
Impacts on target:
Landcare Research (2014c) - fewer thistles observed at some sites; impact unknown.
Cripps, Navukula, Carsonato & van Koten (2020) - twenty randomly-selected pastoral locations from Northland to Southland (10 sites in the North Island, 10 in the South Island) were surveyed from 8 February to 9 March 2018 (late summer to early autumn) during the peak seed production period of C. vulgare. U. stylata was detected at 14 of the sites, and at those sites 37-100% of plants were attacked. Urophora stylata reduced the number of seeds per attacked seedhead by 47%, individual seed weight by 21%, and seed germination rate by 30%. Where U. stylata was present, estimated population seed reduction ranged from 11 to 61%. The impact of the gall fly significantly increased from southern to more northern latitudes. The seed level reduction necessary to cause C. vulgare population decline remains uncertain. Given the impact on seed production and germination rate reported here, population level impacts are probable, especially in northern New Zealand populations where intensity of attack is greatest.
Impacts on non-targets:
Paynter et al. (2004) - surveys of globe artichoke (Cynara scolymus), the only valued thistle in New Zealand, record no U. stylata feeding, as predicted by lab tests.
Hayes (2007d) - extremely unlikely to attack plants other than Scotch thistle and to a lesser extent Californian thistle (Cirsium arvense).
Cripps, Navukula J, Kaltenbach et al. (2020) - surveys in central Europe have recorded U. stylata from Cirsium and Carduus species. The original sources of U. stylata released in New Zealand were in France, Germany, and Switzerland; thus, it is likely that the fundamental host range of New Zealand U. stylata is restricted to Carduus and Cirsium species. Pre-release host specificity testing carried out CABI Switzerland using the Swiss Jura biotype of the fly (considered highly specific to C. vulgare) against 44 test plant species showed oviposition on three tribe Cardueae (thistle) species (Arctium tomentosum,Carduus acanthoides and Onopordum acanthium) other than C. vulgare, but development was completed only on C. vulgare. In additional pre-release host specificity testing carried out in New Zealand and Australia, no native species tested were attacked, and of three thistle weeds (Cirsium arvense, Carduus nutans and Silybum marianum) tested in addition to C. vulgare, attack was detected only on C. arvense (Californian thistle). Post-release assessment was undertaken in Feb/Mar 2018, with a survey of 18 pastures under sheep and/or beef production, where C. vulgare and other thistle weeds were present, across the North and South Islands. In addition to C. vulgare, the gall fly was recorded on C. arvense (six locations) and Cirsium palustre (one location). The probability of attack on C. arvense was positively correlated with attack intensity on C. vulgare, suggesting that attack on C. arvense is a â€˜spill-over effectâ€™ occurring where seedheads of C. vulgare are in limited supply. The data are too limited to determine if the attack on C. palustre is a spill-over effect. In Dec 2019 an opportunistic collection of thistle seedheads from three locations in the Gisborne region showed no U. stylata activity on thistles (C. arvense, Carduus tenuiflorus, S. marianum) other than C. vulgare.
Cripps M, Navukula J, Casonato S, van Koten K. (2020). Impact of the gall fly, Urophora stylata, on the pasture weed, Cirsium vulgare, in New Zealand. BioControl (2020). Published online 18 March 2020. https://doi.org/10.1007/s10526-020-10007-0
Cripps M, Navukula J, Kaltenbach B, van Koten C, Casonato S, Gourlay H. (2020). Spill-over attack by the gall fly, Urophora stylata, on congeners of its target weed, Cirsium vulgare. New Zealand Plant Protection 73: 24â€“32 https://doi.org/10.30843/nzpp.2020.73.11718
Hayes L (2007d). Scotch Thistle Gall Fly. In The Biological Control of Weeds Book (Landcare Research). https://www.landcareresearch.co.nz/discover-our-research/biosecurity/weed-management/using-biocontrol/the-biological-control-of-weeds-book/
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 (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
Paynter, Q.E., Fowler, A.H., Gourlay, M.L., Haines, M.L., Harman, H.M., Hona, S.R., Peterson, P.G., Smith, L.A., Wilson-Davey, J.R.A., Winks, C.J. and Withers, T.M. (2004). Safety in New Zealand weed biocontrol: A nationwide survey for impacts on non-target plants. New Zealand Plant Protection 57: 102-107
Withers TM , Hill RL, Paynter Q, Fowler SV, Gourlay AH. (2008). Post-release investigations into the field host range of the gorse pod moth Cydia succedana Denis & SchiffermÃ¼ller (Lepidoptera: Tortricidae) in New Zealand. New Zealand Entomologist 31(1): 67-76