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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:

UK

Import notes:

Fowler et al. (2000) - line-rearing was undertaken in quarantine, 1995-97, to eliminate a parasitic microsporidian from the heather beetle cultures.

Landcare Research (2013c) - 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, 2014

Release details:

Peterson et al. (2004) - 17 releases totalling 5700 adults 1996-1999 in Tongariro National Park (Central Plateau, North Island); 3 releases at Rotorua 2001.

Peterson (2011) - imported in 1992 but widespread releases were delayed until 1996 due to problems with a protozoan parasite infection.

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) - Nov 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] 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 TNP where beetles had not yet dispersed in 2018 [see Landcare Research (2021c) entry in 'Establishment' section].

Establishment:

Landcare Research (2004a) - only 3 of 64 releases at Tongariro National Park (TNP) seem to have established, while 2 of 3 at Rotorua have.

Peterson et al. (2004) - establishment success low in TNP compared to Rotorua (which is at a much lower altitude), most likely due to climatic conditions.

Landcare Research (2019c) - the recent explosion of the original heather beetle population in the Central Plateau (TNP) suggests that they have now managed to adapt to the conditions, including higher altitude areas.

Landcare Research (2020g) ā€“ uncertain if new strains more suited to high altitudes released recently [see Landcare Research (2015g) entry in ā€˜Release detailsā€™ 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 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 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 3 sites (1 at Tongariro, 2 at Rotorua) the amount of damage caused by large numbers of beetles has been extremely promising.

Peterson et al. (2011) - between 2007 and 2011 populations have grown exponentially at three release sites and severely damaged or killed approximately 100 ha of heather. Impact assessment plots set up in 2008; after 2 years heather cover reduced 99% after heather beetle attack.

Landcare Research (2014c) - 1300 ha heather damaged/killed at Tongariro National Park (TNP) 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 3000 ha of heather in TNP 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 5000 hectares. Every year the damaged area has been growing exponentially and the nett 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 (TNP) suggests that they have now managed to adapt to the conditions, including higher altitude areas.

Landcare Research (2020g) - the beetles have now damaged or killed over 10,000 hectares of heather in TNP, and are spreading rapidly.

Landcare Research (2021c) - dense heather monocultures are fast becoming a thing of the past in and around TNP, and this is now one of New Zealandā€™s great biocontrol success stories.

Landcare Research (2021f) - has damaged or killed 40,000+ hectares of heather at TNP 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 3 years, with large populations damaging vast areas of heather. Trials in 2007 suggested that establishment and population growth could be reduced in 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 -4Ā°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.

Impacts on non-targets:

Fowler et al. (2000) - host range tests were conducted 1991-94 in the UK against 18 species in the Ericaceae, 14 species in the related family Epacridaceae, and 28 other selected plant species from a range of families. In no-choice feeding tests 18 plant species were fed on; in choice feeding tests of these species, four were damaged, including the New Zealand native Pentachondra pumila. Egg-adult development tests were carried out against these four species, and a field test against P. pumila.

Paynter et al. (2004) - surveys record no non-target feeding, despite lab tests predicting minor non-target impacts.

Peterson (2011) - extremely unlikely the beetles will attack plants other than Scotch heather. 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 found as a result of beetle feeding and there is early evidence that native shrub recovery is occurring following biocontrol.

Landcare Research (2019c) - heather regrowth in the beetle 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 beetle-present and beetle-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.

General comments:

Landcare Research (2013c) - males from Scotland imported 2013; will mate Scottish males with New Zealand females and release offspring 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

Effah E, Barrett DB, Peterson PG, Wargent JJ, Potter MA, Holopainen JK, McCormick AC. (2020). Herbivory and attenuated UV radiation affect volatile emissions of the invasive weed Calluna vulgaris. Molecules 2020, 25(14), 3200 https://doi.org/10.3390/molecules25143200

Fowler SV, Peterson P, Barrett DP, Forgie S, Gleeson DM, Harman H, Houliston GJ and Smith L (2015). Investigating the poor performance of the heather beetle, Lochmaea suturalis (Thompson) (Coleoptera: Chrysomelidae), as a weed biocontrol agent in New Zealand: Has genetic bottlenecking resulted in small body size and poor winter survival? Biocontrol 87: 32-38

Fowler SV, Syrett P, Hill RL. (2000). Success and safety in the biological control of environmental weeds in New Zealand. Austral Ecology 25: 553ā€“562

Landcare Research (2004a). Heather beetle blues. What's new in biological control of weeds? 28: 3 https://www.landcareresearch.co.nz/__data/assets/pdf_file/0014/20615/wtsnew28.pdf

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 (2013c). Scottish 'laddies' flown in for genetic rescue. What's new in biological control of weeds? 65: 2 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-65

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 (2015g). Heather beetle set for even greater things. Weed Biocontrol: What's New? 74: 4 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-74

Landcare Research (2019c). Heather beetle gives natives a fighting chance. Weed Biocontrol: What's New? 87, February 2019. https://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-87/heather-beetle-gives-natives-a-fighting-chance

Landcare Research (2020g). Who's who in biological control of weeds? Weed Biocontrol: What's New? 93, Aug 2020. https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/status-of-agents/

Landcare Research (2021c). Improved establishment success of heather beetles, 25 years post release. Weed Biocontrol: What's New? 96, May 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/improved-establishment-success-of-heather-beetles-25-years-post-release/

Landcare Research (2021f). Who's who in biological control of weeds? Weed Biocontrol: What's New? 97, August 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/whos-who-in-biological-control-of-weeds

Landcare Research (2022i). Climate in the heather beetle story. Weed Biocontrol: What's New? 102, November 2022 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/climate-in-the-heather-beetle-story/

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

Peterson P (2011). Heather Beetle. In The Biological Control of Weeds Book (Landcare Research) http://www.landcareresearch.co.nz/research/biocons/weeds/book/documents/Heather_%20Beetle.pdf

Peterson P, Fowler S, Merrett, M and Barrett P (2011). Impact of the heather beetle (Lochmaea suturalis), a biocontrol agent for heather (Calluna vulgaris), in New Zealand. Entomological Society of New Zeland, Ento conference 2011 http://ento.psiconf.com/abstracts/90

Peterson P, Fowler SV and Barrett P. (2004). Is the poor establishment and performance of heather beetle in Tongariro National Park due to the impact of parasitoids, predators or disease? New Zealand Plant Protection 57: 89-93

Peterson PG, Merrett MF, Fowler SV, Barrett DP, Paynter Q. (2020). Comparing biocontrol and herbicide for managing an invasive nonā€native plant species: Efficacy, nonā€target effects and secondary invasion. Journal of Applied Ecology 57: 1876-1884. Published online 2 June 2020. https://doi.org/10.1111/1365-2664.13691