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Biocontrol introduction

Target pest: Ulex europaeus (Fabales: Fabaceae), gorse

Agent introduced: Cydia ulicetana (Lepidoptera: Tortricidae), gorse pod moth


1988?/1989?, 1992

Import source:

England (1988?/1989?); Viana do Castello, Portugal (1992)

Import notes:

Hill & Gourlay (2002) - in 1988, 198 Cydia ulicetana [imported as Cydia succedana but subsequently considered likely to be C. ulicetana (see 'General comments' section)] moths, collected from Yateley Common, Hampshire, England, were imported into containment in New Zealand for evaluation and rearing in quarantine.

Landcare Research (2005a) - gorse pod moths for initial releases were sourced from Yately Common, Hampshire, UK. Later some moths were also sourced from Portugal in an attempt to increase genetic diversity and improve climate matching.

Gourlay (2007b) - Cydia ulicetana is native to Europe and was first imported into New Zealand from England in 1989 and mass-reared for releases.

Withers et al. (2008) - gorse pods moths imported into New Zealand were sourced initially from England. A later, 1992 importation was made from Viana do Castello, Portugal to improve the genetic diversity of the population.



Release details:

Hill & Gourlay (2002) - since 1992, moths have been released at 134 sites throughout New Zealand. At most sites, between 100 and 500 moths were released.

Gourlay (2007b) - released throughout New Zealand in the early 1990s.

Withers et al. (2008) - first released in 1992. The population released into New Zealand contained moths from both England and Portugal to improve genetic diversity.


Harman et al. (1996) - has established well at a site in Canterbury.

Rees & Hill (2001) - Cydia ulicetana has established widely.

Hill & Gourlay (2002) - ninety-three of the 134 release sites are old enough for establishment success to be judged. Of the 64 of these adequately assessed, C. ulicetana has established at 50 (78%). There is no evidence that release size has influenced establishment success. There appears to be no geographical pattern to success or failure of establishment and it seems likely this species will establish throughout New Zealand.

Gourlay (2007b) - now becoming widespread in both North and South Islands.

Hill et al. (2007) - the moth is now abundant throughout gorse-infested areas of New Zealand.

Landcare Research (2014c) - common in many areas.

Impacts on target:

Hill et al. (2000) - Cydia succedana was selected as a control agent on the assumption that the second generation would attack the autumn crop of gorse seeds, that escape attack by the gorse seed weevil (Exapion ulicis), which is active only in spring. The impact of C. ulicetana and E. ulicis was studied at a site in Mid-Canterbury, South Island, where gorse grows on a hillside spanning 100 m in altitude. Contrary to expectations, C. ulicetana densities peaked in spring rather than autumn; it appears that most of the population in New Zealand is univoltine in spring, and the second generation is small. At the bottom of the hill, where seed was set only in spring, the agents together destroyed 90% (range 75-100) of the annual seed crop. At the top of the hill, where gorse sets most seed in autumn, C. ulicetana destroyed 10-20% while E. ulicis was inactive. Elsewhere in the site, gorse produces seed in both seasons, and the impact of the two insects on the annual seed crop varied. As the altitudinal patterns of gorse seed production are repeated latitudinally in New Zealand, reduction in the annual seed production in the south of the country may be large, but in more northern areas may not exceed 50%.

Rees & Hill (2001) - modelling indicates that the potential impact of the seed-feeding biocontrol agents C. ulicetana and Exapion ulicis (gorse seed weevil) on gorse abundance depends critically on large-scale site disturbance, such as fire and herbicide application, and the effects of disturbance on germination and seed mortality. If seedlings have a high probability of survival, then seed-feeding biocontrol agents have little impact on gorse dynamics. However, if seedling survival is low, e.g. as a result of grazing, then these biocontrol agents can have a dramatic impact on gorse abundance. The models highlight the need to manage seedling recruitment opportunities carefully in order to maximise the effect of the biocontrol agents.

Gourlay et al. (2004) - an insecticide exclusion trial in Canterbury, South Island showed that while gorse pod moth has a negative impact on the gorse seed weevil (Epaxion ulicis) the combined effects of the two agents was greater than either alone, with 81% of spring seed destroyed by both agents in combination. Modelling suggests a reduction in the annual seed crop of 75–85% would be sufficient to cause long-term decline in gorse cover. In places where autumn seed production contributes little to the annual seed crop, these two agents may already be contributing to a decline in gorse population density.

Landcare Research (2005a) - gorse pod moths are not having a significant impact on gorse, particularly in the North Island. The reasons for this are not yet known.

Gourlay (2007b) - at a low altitude site in Canterbury C. ulicetana and the gorse seed weevil (Epaxion ulicis) were found to be destroying 90-100% of the spring/summer seed crop (about half each) and gorse pod moth was taking about 15-20% of the winter/autumn seed crop. Early indications are that C. ulicetana infestation levels in the autumn are lower than hoped and this may be due to less-than-optimal synchrony between gorse flowering and pod moth activity.

Hill et al. (2007) - the predicted reduction in autumn seed production has not occurred. There appears to be lack of synchrony between the emergence of moths and the peak occurrence of gorse pods in autumn, and infestation rates rarely exceed 10%. As seed set in autumn forms the bulk of seed production in warmer parts of New Zealand, adequate control of seed production has not yet been achieved.

Withers et al. (2008) - in a spring field survey, at North Island sites, where gorse flowered in November and mature pods opened in January, gorse pod moth infestation levels never exceeded 2% of gorse pods. South Island sites, where gorse flowered in October and mature pods opened in December, had much higher infestation levels, up to 90%.

Sixtus et al. (2013) - from Aug 2009 to April 2011, 15 sites in upper South Island and lower North Island were monitored for gorse pod moth damage. Overall 27% of seed was damaged to point of being non-viable, which indicates gorse control by this agent is not successful, primarily because moth population and gorse flowering is not in synchrony.

Landcare Research (2014c) - can destroy many seeds in spring but not as effective in autumn.

Gourlay (2021b) - a recent study in Canterbury, South Island at a high-altitude site showed join destruction between C. ulicetana and E. ulicis (gorse seed weevil) of just 56% of spring/summer seed crop, with no seed was produced in autumn/winter. The gorse pod moth was taking 14% of the spring/summer seed crop. Recent work in Manawatu, North Island at a low-altitude site showed joint destruction of only 21% of the total crop with the gorse pod moth taking 30% of autumn/winter seed. [See Landcare Research (2023d) entry below for further details.]

Landcare Research (2023d) - surveys at two sites, one in Christchurch in the South Island and one in Palmerston North in the North Island, investigated the impacts of the introduced seed-feeding biocontrol agents (C. ulicetana and the gorse seed weevil, Exapion ulicis) on gorse populations. Total seed production in a season was 6,908 seeds/m2 at Palmerston North, 1,072 seeds/m2 at Christchurch; seed predation by biocontrol agents was 24% at Palmerston North, 60% at Christchurch; resulting in a seed fall of 5,250 seeds/m2 at Palmerston North, 429 seeds/m2 at Christchurch; culminating in a seed bank of 23,695 seeds/m2 at Palmerston North, 4,312 seeds/m2 at Christchurch. Cydia ulicetana accounted for most of the seed predated at the Palmerston North site (17%) while E. ulicis was dominant at the Christchurch site, accounting for 42%. Modelling by Rees & Hill (2001) [see Rees & Hill (2001) entry above] (which found the primary drivers of gorse invasion and cover to be seedling recruitment and survival, and environmental disturbance) indicates that at the Christchurch site, with low seed fall and probable low seedling survival due to grass cover, the population of gorse should reduce over time. The Palmerston North site would need a very high level of disturbance and low seedling survival to reduce the gorse population. Sites throughout the country vary hugely, but managing for low seedling recruitment will be key for obtaining the greatest impact from seed-feeding biocontrol agents. Management practices that kill plants, prevent or substantially reduce subsequent recruitment, and reduce seedling survival will be required to reduce gorse cover, regardless of seed predation levels.

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. ulicetana, a seed feeding moth, have not 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 ‘slight’.

Impacts on non-targets:

Hill & Gourlay (2002) - the physiological capability of C. ulicetana to utilise plant species of conservation or significant economic value was estimated by testing 44 plant species, representing all legume (family Fabaceae) genera in New Zealand, in both the presence and the absence of gorse. Behavioural observations and experiments were then used to infer the likely field host-range from within the physiological host-range. The tests were carried out in the UK and in New Zealand, using moths collected at Yateley Common (the source of the English moths imported into New Zealand), or nearby Chobham Common. The data suggest that there is a low probability that C. ulicetana will colonise or damage any of the non-target plants tested, or any other legumes present in New Zealand, and therefore poses no significant threat to any non-target plants with economic or environmental value in this country.

Paynter et al. (2004), Fowler et al. (2004) - larvae have been found attacking other introduced legumes, such as Scotch broom (Cytisus scoparius) and tree lupin (Lupinus arboreus), though laboratory tests in England predicted no non-target feeding and field records indicated the moth was narrowly oligophagous in Europe. This may be a “spill-over” effect at high moth population density, or due to asynchrony between target plant and agent. Also there may be issues with the provenance of insects since moths released in New Zealand were sourced from both England and Portugal and C. succedana (the name under which gorse pod moth was introduced to New Zealand) was recently split into 2 species (the other being C. ulicetana), and moths resembling both species were collected in New Zealand during non-target surveys. Furthermore, there are forms of difficult assignation present in the Iberian Peninsula that would require some research to determine their taxonomic status. Extensive surveys in New Zealand indicate no native legume species are attacked.

Landcare Research (2005a) - although the level of non-target attack varies between sites, overall it appears to be quite low and probably of no major consequence to these exotic species. The reasons for the non-target attacks are unclear; one possibility is the taxonomies of the moth and the gorse. Moths used for host range testing and initial releases in New Zealand were from Yately Common in the UK; subsequently moths from Portugal were also released. Some taxonomists have recently split the pod moth into two species (C. succedana and C. ulicetana), with English moths considered to be C. ulicetana and the identity of moths in Portugal not yet known. In addition, gorse in the UK and Portugal are different subspecies. All moths looked at in New Zealand appear to be C. ulicetana; however, there does not appear to be any difference between moths collected from gorse and non-target species, so obvious taxonomic differences do not appear to explain the non-target attack.

Withers et al. (2008) - post-release host range trials and field surveys did not detect any attack on native New Zealand plant species, but contrary to predictions based on pre-release host range testing, several species of exotic plants, including Scotch broom Cytisus scoparius, Montpellier broom Teline (Genista) monspessulana, and tree lupin Lupinus arboreus (all tribe Genisteae), as well as lotus Lotus pedunculatus (tribe Loteae) growing in the vicinity of infested gorse plants, were shown to be hosts of gorse pod moth in both the North and South Islands. Three possible reasons for the failure to predict non-target attacks are: a) poor synchrony between host flowering and biocontrol agent activity resulting in less preferred host being used when gorse pods were not available; b) that, as well as C. succedana [subsequently considered likely to be C. ulicetana], a cryptic species was accidentally introduced (closely related Cydia species have now been identified, raising this possibility); and c) that the population from Portugal has a different host-range to the tested (English) population.

Paynter et al. (2008) - gorse pod moth in the field has been found attacking non-targets Cytisus scoparius (Scotch broom), Genista monspessulana (Montpellier broom), Lupinus arboreus (tree lupin), Lotus pedunculatus (lotus), and also occasionally Spartium junceum (Spanish broom), Genista lydia (Lydian broom), Lupinus polyphyllus (Russell lupin), Cytisus proliferus (tagasaste, a minor fodder crop) and Lotus corniculatus (bird's-foot trefoil). These are all non-natives and most are invasive weeds and no adverse environmental or economic impacts have been reported; however, the host-range is broader than was predicted by host-range testing. Experiments and field surveys were carried out to test three hypotheses to explain why original host range testing did not predict the host range in New Zealand: (1) that, as well as gorse pod moth, a cryptic species was accidentally introduced; (2) asynchrony between oviposition of the biocontrol agent and flowering of the target plant, and (3) the population collected in Portugal has different host preferences from the tested English population. Morphology and DNA sequencing indicated that only one Cydia species was present in the New Zealand samples. Host range testing of moths collected at Yately Common, UK (where moths were collected for the original host range tests) did not contradict the original tests that indicated non-target attack was unlikely. In contrast, moths sourced from Portugal were capable of exploiting a broader range of plants, though in choice tests, gorse was preferred. It is concluded that the non-target hosts were not predicted because of the release of untested moths from Portugal and asynchrony between gorse pod moth flight period and gorse flowering causing deprivation and the use of less preferred hosts.

General comments:

Landcare Research (2005a) - some taxonomists have recently split the gorse pod moth into two species: C. succedana and C. ulicetana. Best advice at the moment is that the English pod moths are now considered to be C. ulicetana, but we do not yet know the identity of the moths in Portugal. [Moths from both countries have been released in New Zealand.]

Paynter et al. (2008) - Danilevsky and Kuznetzov (1968) recognized C. succedana (Denis and Schiffermüller) and C. ulicetana (Haworth) as separate species. However, many authorities considered C. ulicetana to be an inferior synonym of C. succedana at the time that gorse pod moth was cleared for release in New Zealand. It was, therefore, introduced into New Zealand under the name C. succedana. Since then, however, Razowski (2003) reinstated the separation between C. succedana and C. ulicetana. There is, consequently, uncertainty regarding the distributions and host-ranges of both species because many literature records do not distinguish between the two. According to this separation, only C. ulicetana occurs in the United Kingdom. It is conceivable that both may occur in Portugal, although only C. ulicetana is currently confirmed to be present there, but several similar closely related Cydia species are present, raising the possibility that a cryptic species may have been accidentally introduced along with gorse pod moth as a culture contaminant [though trials reported in this publication - see 'Impacts on non-targets' section - suggest this did not occur].


Fowler, S.V., Gourlay, A.H., Rill, R.H. and Withers, T. (2004). Safety in New Zealand weed biocontrol: a retrospective analysis of host specificity testing and the predictability of impacts on non-target plants. proceedings of the XI International Symposium on Biological Control of Weeds. Cullen, J.M., Briese, D.T., Kriticos, D.J., Lonsdale, W.M., Morin, L. and Scott, J.K. (Eds). Canberra, Australia, CSIRO Entomology, 27 April - 2 May 2003.

Gourlay AH, Partridge TR, Hill RL. (2004). Interactions between the gorse seed weevil (Exapion ulicis) and the gorse pod moth (Cydia succedana) explored by insecticide exclusion in Canterbury, New Zealand. In: Cullen, J.M., Briese, D.T., Kriticos, D.J., Lonsdale, W.M., Morin L. and Scott, J.K. (eds) Proceedings of the XI International Symposium on Biological Control of Weeds. CSIRO Entomology, Canberra, Australia, pp. 520–522

Gourlay H (2007b). Gorse pod moth: Cydia succedana. 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/gorse-pod-moth/

Gourlay H (2021b). Gorse pod moth: Cydia succedana. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Update of Gourlay (2007b)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/gorse-pod-moth/

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

Hill RL, Gourlay AH (2022). Host-range testing, introduction, and establishment of Cydia succedana (Lepidoptera: Tortricidae) for biological control of gorse, Ulex europaeus L., in New Zealand. Biological Control 25(2): 173-186 https://doi.org/10.1016/S1049-9644(02)00057-9

Hill RL, Gourlay AH, Fowler SV (2000). The biological control program against gorse in New Zealand. In Proceedings of the X international Symposium on Biological Control of Weeds 2000 Jul (Vol. 917, pp. 909-917). Montana State University Bozeman, Montana, USA. https://www.landcareresearch.co.nz/assets/researchpubs/biologial_control_gorse_Hill_2000.pdf

Hill RL, Ireson J, Sheppard AW, Gourlay AH, Norambuena H, Markin GP, Kwong R, and Coombs E. (2007). A global view of the future for biological control of gorse, Ulex europaeus L. In Proceedings of the XII International Symposium on the Biological control of Weeds (eds Julien MH, Sforza R, Bon MC, Evans HC, Hatcher PE, Hinz HL, Rector BG), pp. 680-686. CAB International , Wallingford, UK. http://citeseerx.ist.psu.edu/viewdoc/download?doi=

Landcare Research (2005a). Making sense of field findings. What's New In Biological Control of Weeds? Annual Review, August 2005, 33: 4-5 https://www.landcareresearch.co.nz/assets/Publications/Weed-biocontrol/wtsnew33.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 (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 (2023d). Are gorse seed feeders hungry enough for a change? Weed Biocontrol: What's New? 105, August 2023 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/are-gorse-seed-feeders-hungry-enough-for-change/

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 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, Gourlay AH, Oboyski PT, Fowler SV, Hill RV, Withers TM, Parish H and Hona SR (2008). Why did specificity testing fail to predict the field host-range of the gorse pod moth in New Zealand? Biological Control 46: 453-462

Rees M, Hill RL (2001). Large-scale disturbances, biological control and the dynamics of gorse populations. Journal of Applied Ecology 38(2): 364-377 https://doi.org/10.1046/j.1365-2664.2001.00598.x

Sixtus CR, Hampton JG, Glare TR and Hill GD (2013). Is the gorse pod moth an effective biocontrol agent of gorse in New Zealand? The role of weed science in supporting food security by 2020. Proceedings of the 24th Asian-Pacific Weed Science Society Conference, Bandung, Indonesia, October 22-25, 201: 294-298

Withers TM , Hill RL, Paynter Q, Fowler SV, Gourlay AH. (2008). Post-release investigations into the field host range of the gorse pod moth Cydia succedana Denis & Schiffermüller (Lepidoptera: Tortricidae) in New Zealand. New Zealand Entomologist 31(1): 67-76 https://doi.org/10.1080/00779962.2008.9722168