Target pest: Hypericum perforatum (Malpighiales: Hypericaceae), St John's wort
Agent introduced: Zeuxidiplosis giardi (Diptera: Cecidomyiidae), St John's wort gall midge
Hancox et al. (1986), Cameron et al. (1989) - released in northern and central South Island, as far south as Wanaka (Otago).
Hancox et al. (1986) - has established well and reaches high densities in the stony riverbeds of the northern South Island. It is also present, although only in low numbers, to an altitude of 830 m in North West Nelson where there is considerable winter snowfall.
Landcare Research (2014c) - established in northern South Island.
Impacts on target:
Hancox et al. (1986) - it has been observed that where pockets of maximum galling occur there is no flowering and that seedlings are killed by midge activity. Recently, however, Dimeromicrus sp. [Cameron et al. (1989) reports this as Torymoides sp.], a hymenopteran parasitoid, has been recorded from Z. giardi in the Nelson area. It is not known whether mortality from this parasitoid is significant.
Cameron et al. (1989) - impacts unknown, may stunt plants.
Landcare Research (2014c) - often causes severe stunting.
Paynter et al. (2018) - Z. giardi is localised and ineffective. Heavily parasitised (41% parasitism) to an extent that is likely to significantly influence its efficacy.
Impacts on non-targets:
Paynter et al. (2004) - lab testing predicted severe non-target damage, and potentially underestimated non-target impacts in that Hypericum gramineum and the natives H. perforatum and H. japonicum weren't tested. Surveys on H. gramineum and H. japonicum are on-going and it is too early to assess non-target impacts, but to-date no non-target feeding has been observed.
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Hancox NG, Syrett P, Scott RR (1986). Biological control of St Johnâ€™s wort (Hypericum perforatum) in New Zealand: a review. Plant Protection Quarterly 1(4): 152-155 https://caws.org.nz/PPQ12/PPQ%2001-4%20pp152-155%20Hancox.pdf
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, Fowler SV, Groenteman R. (2018). Making weed biological control predictable, safer and more effective: perspectives from New Zealand. BioControl 63: 427â€“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
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