Biocontrol introduction
Target pest: Calluna vulgaris (Ericales: Ericaceae), heather
Agent introduced: Lochmaea suturalis (Coleoptera: Chrysomelidae), heather beetle
Imported:
1992, 1993, 1994, 2000, 2013
Import source:
England (1992, 1993, 1994, 2000), Scotland (2013)
Import notes:
Syrett et al. (2000) - a microsporidian disease that markedly reduces L. suturalis fecundity and longevity has been present in most of the shipments imported into New Zealand from the UK.
Fowler et al. (2000) - line-rearing was undertaken in quarantine, 1995-97, to eliminate a parasitic microsporidian from the heather beetle cultures.
Peterson et al. (2004) - Lochmaea suturalis was sourced from the UK, and underwent five years of host-range testing and environmental impact assessment prior to its release in New Zealand in 1996.
Landcare Research (2007a) - specimens of L. suturalis from the UK, dated 1993, 1994 and 2000, are present in the Biological Control Voucher Collection of the New Zealand Arthropod Collection [indicating importations from the UK in those years].
Fowler et al. (2008) - in 1995, beetles were collected from a range of sites in the UK to ensure a climatic match to Tongariro National Park (the target area for biocontrol of C. vulgaris in New Zealand) and line-reared in quarantine in New Zealand to eliminate a microsporidian disease commonly found in the UK beetles.
Peterson (2011) - Lochmaea suturalis is native to north-west Europe where large scale outbreaks can devastate heather. It was first imported into New Zealand from the UK in 1992 but widespread releases were delayed until 1996 due to problems with a protozoan parasite infection.
Landcare Research (2013c) - the 2013 importation was males from Scotland [see Landcare Research (2013c) entry in 'General Comments' section]. Previous importations were from several sites in England.
Released:
1996 (English beetles), 2014 (Scottish male/New Zealand female offspring)
Release details:
Peterson et al. (2004) - seventeen releases totalling 5,700 adults were made 1996-1999 in Tongariro National Park (TNP) (Central Plateau, North Island); following establishment at the Te Piripiri site [see Fowler et al. (2004) entry in ‘Establishment’ section below], beetles from this site were used to start a laboratory colony at Palmerston North and for further releases around TNP as well as three releases at Rotorua in 2001 [see Fowler et al. (2008) entry below in this section for details].
Fowler et al. (2008) - releases in Tongariro National Park (TNP) in the central North Island of adult beetles reared in quarantine from imported material [see Fowler et al. (2004) entry in ‘Import notes’ section above] were as follows: 1995-96 summer, two releases of 250 beetles each; 1997-98, 13 releases (100-800 per release); 1998-99, two releases (250 per release) - a total of 5,700 beetles released over these three summers. Each of the two 1995-96 releases was from lines reared from single geographic areas in the UK (Oakworth, England and Glencoe, Scotland), but prior to the 1997-98 releases all UK lines were mixed. Following establishment at the Te Piripiri site [see Fowler et al. (2004) entry in ‘Establishment’ section below], beetles were redistributed from this site (directly, and via a rearing colony established from this site) as follows: TNP 2000-01 to 2005-06, 49 releases (adults and/or larvae, 10-6,000 per release - total 7,500); Rotorua (about 130 km north of TNP, at an altitude of 400 m compared to 650-1,300 m for the park sites), three releases (250 per release - total 750).
Landcare Research (2014c) - new strains more suited to high altitude will be released soon [see Landcare Research (2013c) entry in 'General Comments' section].
Landcare Research (2015g) - in November 2014, 300 of the new line of beetles (from recently imported Scottish males mated to New Zealand females) [see Landcare Research (2013c) entry in 'General Comments' section] were released at a low altitude site near Turangi (central North Island) into a field cage to prevent dispersing and improve chances of establishment. More releases of this line will be made this year (2015).
Landcare Research (2021c) - fourteen experimental releases [of the originally-released strain, i.e. redistributed from areas where they had established] were made in four areas of Tongariro National Park where beetles had not yet dispersed in 2018 [see Landcare Research (2021c) entry in 'Establishment' section].
Establishment:
Landcare Research (2004a) - only three of 64 releases at Tongariro National Park seem to have established, while two of three at Rotorua have [see Fowler et al. (2008) entry below in this section].
Peterson et al. (2004) - by 2001 there was only one site, Te Piripiri, where L. suturalis had been established for more than one year. At this site the main heather patch (300 square metres) was impressively damaged, with some heather mortality. The success of releases of beetles relocated from Te Piripiri [see Fowler et al. (2008) entry in ‘Release details’ section above] appears to have been low in the Tongariro area, but higher in Rotorua (which is at a much lower altitude), where two of the three 2001 releases had established by 2002 and were already causing visible damage to heather. Over the same period, the numbers of beetles at Te Piripiri, which had been increasing approximately exponentially from their discovery in 1999, suddenly dropped approximately 10-fold. Trials at Te Piripiri indicate that predation, parasitism disease or food limitation are not responsible for the poor establishment and spread of L. suturalis in Tongariro National Park. Rather, the most likely cause is considered to be adverse weather conditions.
Fowler et al. (2008) - no recoveries were made until summer 1999-2000, when five adult beetles and 20 larvae were found at Te Piripiri in Tongariro National Park (TNP), a January 1996 release site (which received beetles originating only from Oakworth in England). Despite intensive sampling, no recoveries have been made from any of the other 16 1995-99 release sites [see Fowler et al. (2004) entry in ‘Release details’ section above]; an establishment rate of only 6%. At Te Piripiri, beetle numbers increased exponentially from 1999-2000 to 2001-02 but collapsed after this, with the population near extinction by 2005-06. Releases using beetles relocated/reared from the Te Piripiri site were made in TNP and at Rotorua [see Fowler et al. (2004) entry in ‘Release details’ section above]; those in the park suffered from a similar very low establishment rate (two out of 49 sites - 4%) as the original releases, but all three releases at Rotorua established. Local weather conditions were the most likely explanation for both the poor establishment in the park (including the collapse in numbers at Te Piripiri) and the dramatically improved establishment rate at the lower altitude Rotorua sites [see Peterson et al. (2004) entry above in this section]. Beetles collected from the field in New Zealand have proved to be significantly smaller than those from a range of sites in the UK [see Fowler et al. (2015) entry in ‘General comments’ section below]; perhaps small body size increased vulnerability to the prolonged TNP winters.
Peterson, Fowler, Forgie et al. (2011) (in Peterson et al. 2024) - establishment at several Tongariro National Park sites was achieved by 2002, but L. suturalis populations grew and spread only slowly.
Landcare Research (2019c) - the recent explosion of the original heather beetle population in the Central Plateau (at Tongariro National Park) suggests that they have now managed to adapt to the conditions, including higher altitude areas.
Landcare Research (2020g) - it is uncertain if new strains more suited to high altitudes released recently [see Landcare Research (2015g) entry in ‘Release details’ section] have established.
Landcare Research (2021c) - to investigate whether the impressive damage and range expansion of the beetles, after almost failing to establish in the 1990s, was due to adaptation to cope with some of the rigours of the Tongariro National Park (TNP) environment, trials were carried out to determine if establishment success had indeed improved, or whether the high beetle densities were purely the result of exponential population growth. Experimental releases [of the originally-released strain, i.e. redistributed from areas where they had established] were made in four areas of TNP where beetles had not yet dispersed in 2018 and their establishment monitored. Twelve heather beetle populations established from a total of 14 experimental releases (85.7%), compared to a success rate of only 5.6% in the 1990s and 38.9% in the 2000s. This trend for increasing establishment success over more than two decades suggests the beetle explosion in TNP in the past decade is the result of adaptation. However, adaptation is not the only possible explanation; environmental stressors in the TNP region may have been reduced as a result of environmental change, e.g. climate change may have ameliorated the harshness of the TNP climate or increased air pollution may have provided more foliar nitrogen for the beetles. These hypotheses are currently being tested.
Landcare Research (2022i) - Lochmaea suturalis originally imported into New Zealand were sourced from multiple locations in the United Kingdom, but only beetles sourced from Oakworth in England established. This was surprising considering the relatively benign climate of Oakworth versus the relatively harsh climate of Tongariro National Park (TNP), where the beetles were released. It was predicted the more recently released beetles sourced from Scotland would be better adapted to TNP conditions, but for unknown reasons the Scottish population has not survived.
Impacts on target:
Landcare Research (2004a) - at three sites (one at Tongariro, two at Rotorua) the amount of damage caused by large numbers of beetles has been extremely promising.
Peterson et al. (2004) - by 2001 at the Te Piripiri site (Tongariro National Park), the main heather patch (300 square metres) was impressively damaged, with some heather mortality. However, a year later at this site beetle numbers has dropped approximately 10-fold, and establishment was poor at other Tongariro sites. In contrast, two of three 2001 releases at Rotorua had established by 2002 and were already causing visible damage to heather.
Fowler et al. (2008) - at the Te Piripiri release site in Tongariro National Park (TNP), L. suturalis numbers increased exponentially from 1999-2000 to 2000-02, causing severe damage to heather; however, the population collapsed after this, and the beetle established poorly at the other release sites in the park. In contrast, all three 2000-01 releases at Rotorua established and caused severe damage to heather within 2 years. [See Fowler et al. (2004) entries in ‘Release details’ and ‘Establishment’ sections above for release and establishment details.] Starting in spring 2005, a trial in TNP using paired plots with and without fertiliser has investigated the role of nitrogen in L. suturalis establishment and success (increased soil nitrogen has been implicated as a factor causing outbreaks of the beetle in Europe) [see Peterson et al. (2024) entry in this section below for the results of this trial]. In summer 2006-07, there was a second outbreak of L. suturalis in the park, which so far has destroyed heather in an area of about 1 ha. It may be a coincidence, but this outbreak started at the first fertilized release site set up. It may also be significant that the site of the first outbreak, Te Piripiri, was unique among all release sites in receiving a heavy fall of volcanic ash in the winter after the release, which might have produced a nutrient flush. However, overall, in the eleven-plus years since the first release of L. suturalis in New Zealand, it has only suppressed heather over a minute percentage of the infested area.
Peterson, Fowler, Forgie et al. (2011) (in Peterson et al. 2024) - establishment at several Tongariro National Park sites was achieved by 2002, and although promising damage to heather was seen, the beetle populations grew and spread only slowly, taking nine years to damage 17 ha of heather at the best-performing site.
Peterson, Fowler, Merrett et al. (2011) - Lochmaea suturalis populations in Tongariro National Park have slowly established and started to damage or kill heather. Between 2007 and 2011 populations have grown exponentially at three release sites and severely damaged or killed approximately 100 ha of heather. In impact assessment plots set up in 2008, L. suturalis had reduced heather cover by 99% after two years.
Landcare Research (2014c) - thirteen hundred hectares of heather has damaged/killed at Tongariro National Park since 1996.
Fowler et al. (2015) - L. suturalis has underperformed as a biocontrol agent in New Zealand compared to damage it does to native heather in Europe, possibly because New Zealand beetles are genetically bottlenecked [see Fowler et al. (2015) entry in 'General comments' section below].
Landcare Research (2015g) - although nearly 3,000 ha of heather in Tongariro National Park have been killed by the beetle, establishment in some parts of the park has been frustratingly slow.
Landcare Research (2019c) - L. suturalis is finally winning the battle with heather in the central North Island. Until recently the overall impact of the heather beetles was less impressive than hoped, particularly at higher altitudes. The first beetle outbreak was detected at Te Piripiri in late 1999, but beetle populations struggled to repeat that early success until nearly 20 years after the 1996 release, when large outbreaks started to form and gain momentum. The beetles have now damaged or killed heather over 5,000 ha. Every year the damaged area has been growing exponentially and the net reduction of heather is now at landscape levels in some places. In the outbreak areas the majority of heather plants have completely died, with only a small number of plants showing signs of regrowth. It is too early to determine the success of releasing (in 2014) the larger-bodied beetles from Scotland [see 'Release details' and 'General comments' sections] but this approach may no longer be needed. The recent explosion of the original heather beetle population in the Central Plateau (at Tongariro National Park) suggests that they have now managed to adapt to the conditions, including higher altitude areas.
Landcare Research (2020g) - Lochmaea suturalis has now damaged or killed over 10,000 hectares of heather in Tongariro National Park, and is spreading rapidly.
Landcare Research (2021c) - dense heather monocultures are fast becoming a thing of the past in and around Tongariro National Park, and L. suturalis is now one of New Zealand’s great biocontrol success stories.
Landcare Research (2021f) - Lochmaea suturalis has damaged or killed 40,000+ hectares of heather at Tongariro National Park and Rotorua.
Landcare Research (2022i) - following two decades of disappointing results with this project, the performance of L. suturalis has improved dramatically in the last three years, with large populations damaging vast areas of heather. Trials in 2007 suggested that beetle establishment and population growth could be reduced in Tongariro National Park (TNP) by sub-zero cold snaps during spring, which beetles (sourced from Oakworth, England, where such severe spring cold snaps do not occur) emerging from overwintering are ill-adapted to cope with. The same experiment was recently repeated, 14 years on, to see if any adaptation has taken place to explain the recent explosion in L. suturalis numbers. While there appeared to be a trend towards the beetles being better able to withstand -4°C following emergence in spring, there were no significant changes, suggesting that adaptation to out-of-season cold snaps by itself cannot explain the dramatic recent improvement in heather beetle performance in TNP.
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. Damaging impacts of L. suturalis, a defoliating beetle, have been reported in its native range (it is regarded as a serious pest of heather in Europe), it does not have a New Zealand native ecological analogue and its impact in New Zealand is assessed as ‘heavy’.
Peterson et al. (2024) - comparison of nitrogen levels in UK and Tongariro National Park (TNP) heather (2007-11) showed levels 30% higher in the UK, probably a result of the low fertility of the young volcanic, heavily leached TNP soils and low levels of air pollution in New Zealand. In laboratory and field cage trials (2010-11), feeding beetles foliage from fertilised (higher nitrogen level) heather increased L. suturalis oviposition (by 35%) and adult body mass (by 28%). TNP field trials (2005-15) showed better beetle performance (establishment and feeding damage) on fertilised plots than control plots. These results support the hypothesis that low host-plant nitrogen is contributing to the poor performance of L. suturalis as a biocontrol agent in TNP, compared to outbreaks of this beetle in Europe. The effects of low host-plant nitrogen are likely to interact with the small body size, and low over-wintering lipid resources of New Zealand L. suturalis [see Fowler et al. (2015) entry in ‘General comments’ section below], to exacerbate each effect.
Barrett et al. (2024), Landcare Research (2025d) - primary and secondary metabolites of C. vulgaris were analysed in plants from Scotland (within its native range) (plants sampled June/July 2018) and the Central Plateau of the North Island of New Zealand (plants sampled January 2019). The results show a significantly higher number of amplified metabolites, most notably defensive phenylpropanoids, in New Zealand plants, and it is suggested that differences in UV-radiation and soil nutrients could be driving the observed differences. To assess direct causality, further experiments are required; however, the results support the concept of abiotically induced upregulation of key biosynthetic pathways, such as secondary defensive metabolites that enhance herbivore resistance, influencing weed biocontrol agent establishment and effectiveness. For L. suturalis, these amplified metabolites may contribute to a nutritional cascade, exacerbating the effects of low foliar nitrogen levels [see Peterson et al. (2024) entry above in this section] and may help explain the difficulties with the initial establishment and the variable effectiveness of this control agent in New Zealand.
Landcare Research (2025g) - Lochmaea suturalis has virtually eliminated C. vulgaris from all the 60,000+ ha infestation at Tongariro National park and Rotorua.
Impacts on non-targets:
Syrett et al. (2000), Fowler et al. (2000) - host range tests were conducted 1991-94 in the UK and in containment in New Zealand against five ornamental varieties of Calluna vulgaris in addition to the wild form, five Erica species, 14 other species within the family Ericaceae including seven New Zealand native Gaultheria species, 15 native New Zealand species and two European species from the related family Epacridaceae, one species from the related family Clethraceae, and 26 plants (including both economically important species and native New Zealand species) from other families. In no-choice feeding tests 18 plant species were fed on; in choice feeding tests of these species, some feeding at least occurred on all but one of these plants, including substantial adult feeding damage to the New Zealand native sub-shrub Pentachondra pumila. However, in larval feeding and development tests, larvae developed to adults only on three Erica species. All larvae on P. pumila died as first instars, and a field test in the UK confirmed that under natural conditions this plant does not support L. suturalis development. These results confirm experience from Europe that L. suturalis is highly host specific and probably feeds and develops only on Calluna under most field conditions and poses a negligible threat to native New Zealand plants. However, some Erica species may also be suitable hosts. Ornamental cultivars of Calluna are suitable hosts but are unlikely to be severely affected because L. suturalis requires a damp understorey of moss or litter for successful oviposition and pupation, which is rarely present in gardens.
Paynter et al. (2004) - field surveys record no non-target feeding by L. suturalis, despite laboratory tests predicting minor non-target impacts.
Peterson (2011) - it is extremely unlikely L. suturalis will attack plants other than C. vulgaris. Beetles may be found on Spanish heath (Erica lusitanica) and other Erica species, but they are not considered to be suitable hosts.
Peterson et al. (2011) - no non-target impacts have been found as a result of L. suturalis feeding and there is early evidence that native shrub recovery is occurring following biocontrol.
Landcare Research (2019c) - heather regrowth in the L. suturalis outbreak areas and the extent to which native plants will replace the heather will be monitored. There may be changes in the soil nutrient loads as the heather dies and decomposes that will initially favour exotic grasses, but as the nutrient flush gradually declines, conditions more favourable to native plants are expected. Already there is evidence that native plants such as Dracophyllum subulatum remain healthy in areas once dominated by heather, and that the heather is being replaced by native tussocks within some of the trial plots.
Effah et al. (2020) - in a comparison of L. suturalis-present and L. suturalis-absent sites on the Central Plateau, a lower number of generalist arthropod herbivores, especially thrips and lepidopteran larvae, was recorded on heather at the site where L. suturalis was present. Specialist herbivores like L. suturalis may be less negatively impacted by the defences built up by their host plant compared to generalists. However, the variation in arthropod communities between the beetle-absent or -present sites could also be attributed to changes in the quality and quantity of the plant food source. Generalist herbivores may avoid heather plants attacked by L. suturalis because food is less available or assimilable due to the induction of chemical defences. Fewer spiders were also recorded at the beetle-present site than the beetle-absent site at two of the four sampling periods.
Peterson et al. (2020) - a five year field trial on the Central Plateau compared control of heather by biocontrol (L. suturalis) and a selective herbicide. Ground cover of monocotyledonous plants (native and non-native) increased after both treatments, while dicotyledonous plant cover (native and non-native) increased only after biocontrol. As native dicots are the most species-rich indigenous plant group in this ecosystem, and non-native dicots only a minor component, benefits to the native flora were consequently greatest in the biocontrol treatment. There was no evidence of L. suturalis feeding on non-target plants during this study.
Effah et al. (2022) - a study investigating the influence of plant cues on the host searching behaviour of L. suturalis and the New Zealand native beetle Pyronota festiva (manuka beetle), using the plants C. vulgaris and the native Leptospermum scoparium (manuka), found L. suturalis showed high host specificity to C. vulgaris plant cues (olfactory, visual, gustatory and tactile), suggesting that it retains its high host-specificity, and that host switch or host range expansion is unlikely to occur.
General comments:
Landcare Research (2013c) - males from Scotland were imported in 2013; Scottish males will be mated with New Zealand females and offspring released to try to develop a population more suited to the harsh climatic conditions of the Central Plateau.
Fowler et al. (2015) - New Zealand beetles are genetically bottlenecked - line-rearing prior to release to eliminate a microsporidian disease and poor establishment led to the New Zealand population being derived from one or 2 females from one UK site. New Zealand beetles are smaller, have less lipids and lower winter survival than UK beetles. Northern UK beetles are larger than and genetically distinct from southern UK beetles - large UK beetles could be used to genetically rescue New Zealand populations.
References
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