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Biocontrol introduction

Target pest: Hypericum perforatum (Malpighiales: Hypericaceae), St John's wort

Agent introduced: Chrysolina hyperici (Coleoptera: Chrysomelidae), lesser St John's wort beetle



Import source:

England via Australia

Import notes:

Hancox et al. (1986) - in December 1943, 30,000 adults of C. hyperici were imported from Australia for control of St John's wort. This insect was chosen for an entirely pragmatic reason: it was the only species to have reached a sufficiently large population for collection and redistribution.

Cameron et al. (1989) - the Australian C. hyperici population, from which the New Zealand population was derived, originated in England.

Groenteman (2014) - Chrysolina hyperici is native to Europe and western Asia and was imported into New Zealand from Australia in 1943.



Release details:

Hancox et al. (1986), Cameron et al. (1989) - the 30,000 adults imported from Australia in 1943 were all released in the Awatere Valley, Marlborough, after one day in quarantine. By December 1946 the Awatere Valley population was sufficiently large for collection and redistribution to Cromwell and Arrowtown in Otago. From 1947 to 1950, C. hyperici was distributed lo a large number of locations throughout New Zealand, although it should be noted that most of the North Island releases were intended for control of a related weed, tutsan (Hypericum androsaemum).


Hancox et al. (1986) - Chrysolina hyperici readily established from the initial release at Awatere Valley.

Cameron et al. (1989) - Chrysolina hyperici is now established on H. perforatum throughout New Zealand.

Syrett (1997) - most common and widespread of the three agents released against H. perforatum, found throughout distribution of the weed.

Groenteman (2014), Landcare Research (2014c) - Chrysolina hyperici rapidly became widely established and can be found on St John's wort throughout the country. Appears to be more common than the Greater St John's wort beetle [C. quadrigemina, also released as a biocontrol for H. perforatum - see the C. quadrigemina introduction entry].

Impacts on target:

Hancox et al. (1986) - by December 1947, four years after the release of C. hyperici over 180 ha of densely infested country in the Awatere Valley had been cleared of St John's wort, and the weed population level here has remained at a low level ever since. However, it should be noted that pasture improvement and rabbit control programmes may have also played a part in reducing St John's wort infestations over this period. From anecdotal reports from other regions it seems that the level of control achieved by C. hyperici has varied considerably both spatially and temporally. In an insecticide exclusion trial near Lake Tekapo, Canterbury, 1983-85, C. hyperici significantly reduced the amount of St John’s wort.

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.

Cameron et al. (1993) - Chrysolina hyperici is categorised as exerting “partial” control (defined as “additional control remains commonly necessary but…pest outbreaks occur less frequently”) over Hypericum perforatum.

Harman et al. (1996) - has had a significant impact on St John's wort.

Syrett (1997) - Chrysolina hyperici occurs in mixed populations with C. quadrigemina where the latter occurs and occasionally outbreaks of these chrysomelids completely defoliate plants. Chrysolina hyperici seems to be the dominant species in New Zealand - studies indicate its reproductive diapause strategy is more 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 greater St John's wort beetle (C. quadrigemina) extremely effective at controlling St John's wort. Believed to be more significant than C. quadrigemina, C. hyperici nearly always provides excellent control.

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, Barringer et al. (2023), Landcare Research (2023i) - investment in H. perforatum biocontrol totalled NZ$0.28 million (2022 rates) associated with the 1943-1992 releases of the chrysomelid beetles, Chrysolina hyperici and C. quadrigemina, 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. [NB: the success of the biocontrol programme is attributed to C. hyperici and C. quadrigemina; Z. giardi is considered localised and ineffective - see the Z. giardi introduction record.] 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.

Fowler, Groenteman & Paynter (2023), Landcare Research (2023h) - a cost-benefit analysis of all weed biocontrol programmes in New Zealand showed that in 2022 investment in weed biocontrol in the productive sector (targeting agricultural as opposed to environment weeds) was NZ$0.69 million, with the three most economically successful weed biocontrol programmes in New Zealand - against ragwort (Jacobaea vulgaris), St John’s wort (Hypericum perforatum) and nodding thistle (Carduus nutans) - yielding a combined annual benefit of NZ$84.7 million.

Paynter (2024) - factors influencing the success of weed biocontrol agents released and established in New Zealand were investigated. Each agent’s impact on the target weed in New Zealand was assessed as ‘heavy’, ‘medium’, ‘variable’, ‘slight’ or ‘none’, where a ‘heavy’, ‘medium’ or ‘variable’ impact have all been observed to reduce populations or percentage cover of their target weed in all or part of their respective target weed ranges in New Zealand. Results showed that: (i) agents that are highly damaging in their native range were almost invariably highly damaging in New Zealand; (ii) invertebrate agents with a closely related ‘native analogue’ species are susceptible to parasitism by the parasitoids that attack their native analogues and failed to have an impact on the target weed, and (iii) agent feeding guild helped predict agent impact - in particular, agents that only attack reproductive parts of the plant (e.g., seed and flower-feeders) are unlikely to reduce weed populations. The impacts of C. hyperici, a defoliating beetle, in its native range are unknown (no reports could be found), it does not have a New Zealand native ecological analogue and its impact in New Zealand is assessed as ‘heavy’.

Impacts on non-targets:

Hancox et al. (1986) - extensive starvation tests using C. hyperici had been conducted in Britain and Australia prior to release in Australia and 13 years of Australian experience had confirmed its host specificity.

Fowler et al. (2000) - causes (as anticipated pre-release) minor damage to Hypericum androsaemum (tutsan) [a significant weed in New Zealand].

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 by C. hyperici has been observed.

Groenteman (2014) - under artificial conditions in the laboratory 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 the former is a 'full' host (can support breeding populations), and minor 'spill-over' feeding on the latter.

Groenteman (2021) - Chrysolina hyperici will only attack St John’s wort (Hypericum perforatum) and possibly some other Hypericum species. Under artificial conditions in the laboratory, the beetles will accept other Hypericum species as hosts, and this can translate to transient spill-over attack in field situations where these species grow near St John’s wort.

Landcare Research (2023c) - in 2008 of a small population of St John’s wort beetles (C. hyperici and Chrysolina quadrigemina) 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.


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Landcare Research (2023i). The economic benefits of two beetles. Weed Biocontrol: What's New? 106, November 2023. https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/the-economic-benefits-of-two-beetles/

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