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Biocontrol introduction

Target pest: Buddleja davidii (Lamiales: Scrophulariaceae), butterfly bush, buddleia

Agent introduced: Cleopus japonicus (Coleoptera: Curculionidae), buddleia weevil, mokai



Import source:

Hunan, China

Import notes:

Withers (2011) - Cleopus japonicus is native to China and a population was imported from Hunan into quarantine in Rotorua in 1993 for host testing.



Release details:

Landcare Research (2007b) - first released September 2006 at Whakarewarewa Rorest, Rotorua.

Watson (2007, 2008) - five additional release sites have been established in North Island plantations (Whakarewarewa, Kinleith, Lake Taupo, Esk, and Rawhiti Forests) between October 2006 and January 2007.

Watson (2008) - further releases were made in the Kaikoura (South Island) area, and Whanganui, Masterton, and Bay of Plenty in the North Island between November 2007 and February 2008.

Withers (2011) - C. japonicus has now been released at over 30 sites in the North and South Islands.

Watson et al. (2011) - one thousand C. japonicus adults were released at each of five commercial forest sites in the North Island 2006 – 2007 [see above entries]. A further 33 releases of approximately 14,910 C. japonicus were made up to 2011, mostly in the North Island, but including three South Island sites (Nelson, Kaikoura, Buller). Other releases have also been made within commercial forest estates in the past two years.


Watson (2007) - early signs are that C. japonicus is doing well at all sites, with a number of generations recorded. Weevils and larvae have been found up to 30 m from the release point.

Watson (2008) - C. japonicus can be considered established at all initial release sites (Whakarewarewa, Kinleith, Lake Taupo, Esk, and Rawhiti Forests) as more than two generations have been recorded, weevils were found after winter, and numbers have increased. Feeding has been found 145 m from the release plants at Kinleith and 200 m from them at Lake Taupo.

Watson (2010) - this autumn, buddleia leaf weevils, larvae and their feeding have been found more than 10 km from the release plants at Kinleith and more than 4 km from the release at Esk Forest. Indications are that spread at Whakarewarewa Forest has also been considerable. The other initial release sites have yet to be checked.

Watson et al. (2011), Watson (2011) - C. japonicus is known to have established at all 38 release sites (with the possible exception of the 2007 release at Upper Hutt, North Island), including a release of only 17 adults in Hawke’s Bay, North Island. This autumn (2011) there are records of C. japonicus being found throughout the Bay of Plenty, up to 50 km from the release sites and rapidly increasing in population density. This includes the Whakarewarewa Forest site in Rotorua, which seemed to perform poorly in the first three years after release. The releases made within commercial forest estates in the past two years have not been revisited to ascertain C. japonicus establishment and dispersal.

Impacts on target:

Watson (2007) - feeding damage to buddleia plants within the central release area at initial release sites (Whakarewarewa, Kinleith, Lake Taupo, Esk, and Rawhiti Forests) is considerable, with weevils feeding on both new and old foliage.

Watson (2008) - it is only early days, but feeding damage to some plants at initial release sites is impressive.

Watson (2010) - The feeding damage to buddleia has been impressive, with over 90% defoliation of buddleia plants within at least 500 m of the release sites at Kinleith and Esk. Damage at Whakarewarewa has also been high, but more patchily distributed.

Watson et al. (2011) - recent observations of complete defoliation of B. davidii bushes within 1 km of several of the original release sites in the past two to three seasons suggests that growth suppression of buddliea is likely.

Watson (2011) - this year there as been a lot more damage to B. davidii, with large areas completely defoliated by C. japonicus. Observations indicate that the weevil is sensitive to microclimate variability. At warmer sites it has often shown a preference for gullies, while at cool sites it preferentially attacks the buddleia in more open, sunny positions.

Withers (2011) - the buddleia leaf weevil is proving to be effective in controlling buddleia. Observations at numerous sites indicate that once the weevil builds up to a high density it will completely defoliate buddleia plants from late summer right through to spring, but it may take 3 years of this defoliation to reduce plant growth or kill plant completely.

Paynter et al. (2018) - C. japonicus is abundant with persistent damaging outbreaks.

Landcare Research (2020f) - persistent and extensive defoliation of buddleia by C. japonicus year after year, which eventually kills even large buddleia plants, has been observed over most of the range of buddleia in New Zealand. In Northland and Rotorua, for example, buddleia has become a rarity, bar a few isolated specimens. The only areas where damage by the leaf weevil is not consistent is at the very edges of its climatic range, around Queenstown and Mt Cook, where it is suspected the weevil population is knocked back each winter and recovers too slowly in spring to reach damaging densities. Overall, the buddleia biocontrol programme has been highly successful.

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 C. japonicus, a defoliating beetle, have been reported in its native range, it does not have a New Zealand native ecological analogue and its impact in New Zealand is assessed as ‘heavy’.

Impacts on non-targets:

Hill (2003) - host range testing of 35 plant species belonging to 24 families outside the Scrophulariaceae and Buddlejaceae indicated none were acceptable hosts of C. japonicus, strongly suggesting there is negligible risk to important New Zealand plant species outside of these families. Some larvae (20%) could complete development on two New Zealand native Scrophulariaceae species tested: Glossostigma elatinoides and Limosella lineata. However, adult females would not lay eggs on these species, suggesting it is very unlikely that C. japonicus could develop self-sustaining populations on any native plant species. Tests on Scrophulariaceae species not native to New Zealand, including 13 Buddleja species, showed 8 Buddleja species, and the European species Verbascum virgatum and Scrophularia aquatica (syn S. auriculata) appeared to be at least partial hosts, suggesting C. japonicus could produce self-sustaining populations on species other than B. davidii in New Zealand. Potential consequences of this vary from species to species; some are valued plants, others potential weeds. B. salvifolia, valued as fodder for bees, was considered not to be a host.

Watson et al. (2009) - laboratory host range testing predicted the two exotic weeds Scrophularia auriculata and Verbascum virgatum (the only non-target plant shown in the lab to be a full host i.e. supporting full development of C. japonicus) were the most at-risk non-target potential hosts, followed to a much lesser extent by the natives Myoporum laetum, Hebe speciosa, Glossostigma elatinoides and Limosella lineata. In 2006/07 an open-field trial confirmed the lab predictions, with some feeding on the non-natives and only minor exploratory feeding at best on M. laetum and H. speciosa, indicating no native plants are under threat of significant attack by C. japonicus.

Watson (2010) - despite high defoliation of the target plant, there has been no damage to other species at release sites with the exception of feeding on the closely related weed species Scrophularia auriculata, which was predicted by pre-release testing.

EPA Applications:

EPA (2005a) - 12 Dec 2003: application by New Zealand Forest Research Institute (Scion) to import and release the weevil Cleopus japonicas for the purpose of biological control of the plant Buddleja davidii. EPA Application # NOR02001, approved without controls 30 Nov 2005.


EPA (2005a). EPA application NOR02001: to import for release the weevil Cleopus japonicus for the purpose of biological control of the plant Buddleja davidii. Environmental Protection Authority website https://www.epa.govt.nz/database-search/hsno-application-register/view/NOR02001

Hill R. (2003). Application to EPA (NOR02001) for the release of a leaf weevil [Cleopus japonicus] for biological control of buddleia. Environmental Protection Authority website https://www.epa.govt.nz/assets/FileAPI/hsno-ar/NOR02001/c7b0337440/NOR02001.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 (2007b). Buddleia weevil welcomed. What's New in Biological Control of Weeds 39, February 2007 https://www.landcareresearch.co.nz/publications/weed-biocontrol/

Paynter Q (2024). Prioritizing candidate agents for the biological control of weeds. Biological Control, Volume 188, January 2024, Article Number 105396 https://doi.org/10.1016/j.biocontrol.2023.105396

Paynter Q, Fowler SV, Groenteman R. (2018). Making weed biological control predictable, safer and more effective: perspectives from New Zealand. BioControl 63: 427–436 (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

Watson M (2007). Buddleia biological control agent off to a good start. Forest Health News, No. 169, January 2007 https://www.scionresearch.com/__data/assets/pdf_file/0003/3873/fhNewsNo169Jan07.pdf

Watson M (2008). Buddleia leaf weevil update. Forest Health News, No. 181, February 2008 https://www.nzffa.org.nz/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Beneficial-organisms/buddleia-leaf-weevil/buddleia-leaf-weevil-update/

Watson M (2010). Buddleia biological control agent on the move. Forest Health News. No 204, April 2010 https://www.nzffa.org.nz/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Beneficial-organisms/buddleia-leaf-weevil/buddleia-biocontrol-on-the-move/

Watson M (2011). Buddleia biological control looking promising. Forest Health News No. 215, May 2011 https://cdm20044.contentdm.oclc.org/digital/collection/p20044coll2/id/109/rec/106

Watson MC, Withers TM and Hill RL (2009). Two-phase open-field test to confirm host range of a biocontrol agent Cleopus japonicus. New Zealand Plant Protection 62: 184-190

Watson MC, Withers TM, Heaphy M. (2011). Cleopus japonicus: Releases and distribution of the buddleia biological control agent in New Zealand. New Zealand Plant Protection 64:155-159

Withers T (2011). Buddleia leaf weevil: Cleopus japonicus. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Updated 2021] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/buddleia-leaf-weevil/