Target pest: Hypericum perforatum (Malpighiales: Hypericaceae), St John's wort
Agent introduced: Chrysolina quadrigemina (Coleoptera: Chrysomelidae), greater St John's wort beetle
Europe via Australia (1963), Europe via Canada (1990)
Hancox et al. (1986), Fraser & Emberson (1987), Cameron et al. (1989) - a second European species of Chrysolina, C. quadrigemina, was introduced from Australia into New Zealand as a biocontrol agent for H. perforatum [following the introduction of C. hyperici - see the Chrysolina hyperici introduction record] in 1963.
Harman et al. (1996) - a new population of C. quadrigemina thought to be better adapted climatically for New Zealand was introduced from Canada in 1990.
1963 (from Australia); 1990 (from Canada)
Fraser & Emberson (1987) - in 1963 an unrecorded number of beetles were released at two sites in Marlborough. Between 1965 and 1968, 152,000 were released at 10 sites in Canterbury and Otago.
Harman et al. (1996) - beetles from Canada, thought to be better adapted climatically for New Zealand, were released in 1990.
Fraser & Emberson (1987) - four C. quadrigemina were collected at Ben Ohau (Canterbury) in 1977 but apart from this collection the species had not been recovered in New Zealand since its release and its survival was uncertain, particularly as further checks at the collection site at Ben Ohau in 1978 and 1981 failed to confirm the presence of the beetle. However, in 1984 C. quadrigemina was rediscovered at two widely separate localities: Wairau Valley, in Marlborough and Clyde and Tarras (about 50km from Clyde) in Central Otago. It seems that C. quadrigemina is probably widely distributed in the South Island, but perhaps patchily, and is only present in relatively low numbers compared to C. hyperici (lesser St John's wort beetle).
Harman et al. (1996) - recoveries of beetles from Canada released in 1990 have been made.
Groenteman (2014) - initially appeared to have disappeared, but has become common in recent times, and can be found on St John's wort infestations in most places.
Impacts on target:
Cameron et al. (1989) - of the two St John's wort beetles introduced (C. hyperici and C. quadrigemina), C.hyperici is the only one to have become successfully established and reached sufficiently high populations to have had an impact on its host plant.
Syrett (1997) - occurs in mixed populations with Chrysolina hyperici and occasionally outbreaks of these chrysomelids completely defoliate plants. Not as widespread or dominant as C. hyperici - studies indicate its reproductive diapause strategy is less successful in areas with colder winters. There are no longer reports of areas in New Zealand where St John's wort is a problem weed; it is concluded successful biocontrol is at least partially responsible.
Groenteman (2014), Landcare Research (2014c) - with the lesser St John's wort beetle (C. hyperici) extremely effective at controlling St John's wort, though not believed to be as significant as C. hyperici.
Landcare Research (2014d), Groenteman (2014) - recent insecticide exclusion trials have showed that it is St John's wort beetles (C. quadrigemina and C. hyperici) rather than other factors that have reduced the weed's abundance. A recent economic analysis has estimated that the Net Present Value of introducing the beetles is between $140 and $1,490 million over 70 years, a benefit to cost ratio of 10:1 and 100:1 respectively.
Fowler et al. (2023) - investment in H. perforatum biocontrol totalled NZ$0.28 million (2022 rates) associated with the 1943-1992 releases of the chrysomelid beetles, Chrysolina quadrigemina and C. hyperici, and the cecidomyiid gall midge, Zeuxodiplosis giardi. Modelling shows biocontrol effectiveness increased linearly from 1943 to reach 99% control nationwide by 1993 (when H. perforatum was no longer considered a significant agricultural weed). It is estimated that H. perforatum biocontrol in New Zealand provided a national benefit of NZ$15.5 million in 2022, with a historical benefit-cost ratio of 6,254:1. Uncertainties remain concerning whether biocontrol caused all reductions in H. perforatum, or whether infestations of this weed were partially replaced by other weeds. Despite such caveats, benefits of H. perforatum biocontrol to New Zealand appear huge and sustainable.
Impacts on non-targets:
Paynter et al. (2004) - field surveys of two native plant species related to H. perforatum, Hypericum gramineum and H. japonicum, were undertaken. Pre-release laboratory testing predicted severe non-target damage, but potentially underestimated non-target impacts in that H. gramineum and H. japonicum weren't tested. Surveys on these species are on-going and it is too early to assess non-target impacts, but to-date no non-target feeding has been observed by C. quadrigemina, although this species, which is adapted to warmer climates, has been recorded feeding on H. gramineum in Australia.
Groenteman (2014) - under artificial conditions in the lab will accept other Hypericum species as hosts, but this has not been replicated in the field.
Paynter et al. (2015) - surveys of potential non-target hosts the natives Hypericum involutum and H. pusillum showed minor 'spillover' feeding on both.
Landcare Research (2023c) - in 2008 of a small population of St Johnâ€™s wort beetles (C. quadrigemina and Chrysolina hyperici) was discovered that appeared to be persisting on a population of native Hypericum species (a mix of mainly H. involutum with some H. rubicundulum). Best-practice host-specificity testing at the time the beetles were released was focused on crop species and neglected to test closely related native hosts. Retrospective tests in 2008-09 have shown that the native plant species are indeed within the fundamental host range of the beetles, which can complete development on H. involutum in the laboratory just as well as they do on H. perforatum. Yet populations of H. involutum in nature do not appear to be under attack, other than this one small population discovered in 2008. Research is underway to identify microbial taxa that are specific to the insect and to the host plant, comparing European and New Zealand insect and plant specimens. Intraspecific microbiome variation could drive the evolution of host range shifts and help explain why the beetles are persisting on H. involutum at the 2008-discovered site.
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.
Fowler SV, Barringer J, Groenteman R, Humphries G (2023). Biocontrol of St Johnâ€™s wort (Hypericum perforatum) provides huge ongoing benefits to New Zealand agriculture. New Zealand Journal of Agricultural Research. Published online 20 Jul 2023. https://doi.org/10.1080/00288233.2023.2232762
Fraser B, Emberson R (1987). Rediscovery of Chrysolina quadrigemina (Suffrian) (Coleoptera: Chrysomelidae) in New Zealand. New Zealand Entomologist 9(1): 57-59 https://doi.org/10.1080/00779962.1987.9722494
Groenteman R (2014). St John's wort beetles. 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/
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
Harman HM, Syrett P, Hill RL, Jessep CT. (1996). Arthropod introductions for biological control of weeds in New Zealand, 1929 - 1995. New Zealand Entomologist, 19(1): 71-80
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 (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 (2014d). Whodunnit? Solving the case of the disappearing St John's wort. What's new in biological control of weeds? 68: 7 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-68
Landcare Research (2023c). Focusing on the insect microbiome. Weed Biocontrol: What's New? 105, August 2023 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/focusing-on-the-insect-microbiome/
Paynter QE, Fowler AH, Gourlay AH, Haines ML, Harman HM, Hona SR, Peterson PG, Smith LA, Wilson-Davey JRA, Winks CJ, Withers TM (2004). Safety in New Zealand weed biocontrol: A nationwide survey for impacts on non-target plants. New Zealand Plant Protection 57: 102-107 https://journal.nzpps.org/index.php/nzpp/issue/view/vol57
Paynter QE, Fowler SV, Gourlay AH, Peterson PG, Smith LA and Winks CJ (2015). Relative performance on test and target plants in laboratory tests predicts the risk of non-target attack in the field for arthropod weed biocontrol agents. Biological Control 80: 133-142 https://doi.org/10.1016/j.biocontrol.2014.10.007
Syrett P (1997). Biological control of St. John's wort in New Zealand. Plant Protection Quarterly 12 (2): 88-90