Biocontrol introduction
Target pest: Jacobaea vulgaris (Asterales: Asteraceae) = Senecio jacobaea, ragwort
Agent introduced: Longitarsus jacobaeae (Coleoptera: Chrysomelidae), ragwort flea beetle
Imported:
1981
Import source:
Italy via Oregon, USA
Import notes:
Cameron et al. (1989) - Longitarsus jacobaeae was introduced into New Zealand from Oregon, USA in 1981, from beetles originating from an Italian strain imported into USA from Europe in the 1960s.
Released:
1983
Release details:
Cameron et al. (1989) - releases were made at 27 sites throughout New Zealand between April 1983 and April 1986. Each release comprised between 230 and 1,500 adults (most releases were of 500), with a total of 14,430 adults released.
Syrett et al. (1991) - between the summers of 1982-83 and 1990-91, 110 releases of L. jacobaeae were made at 106 sites throughout New Zealand. Most releases comprised 300 adult beetles.
Harman et al. (1996) - now being actively redistributed from established field populations by noxious plants officers and farmers.
Gourlay (2007h) - released widely in late 1980s and early 1990s.
Establishment:
Syrett et al. (1991) - L. jacobaeae has established at 75% of the 1982/83 - 1990/91 release sites. Beetles were found to have spread about 90 m after 2-3 years and over 300 m in 4-6 years. At one site, beetles were found 1 km from the release point after six years. Ragwort flea beetle is now well established at a number of sites throughout New Zealand.
Harman et al. (1996) - now well established throughout the distribution of ragwort in New Zealand.
Gourlay (2007h) - now established in every region of New Zealand.
Impacts on target:
Syrett et al. (1991) - at 11 of 15 release sites (where appropriate data was collected) where L. jacobaeae had been established in 1987 or earlier (and no other biocontrol agents were present), a decline in ragwort abundance was observed over an increasing area as beetles spread from the release point in successive years. Ragwort abundance decreased at all 3 sites where both L. jacobaeae and Tyria jacobaeae (cinnabar moth) were established, suggesting these two agents may be complementary in their impact on ragwort populations.
Harman et al. (1996) - there are many anecdotal reports of L. jacobaeae greatly reducing the amount of ragwort.
Gourlay (2007h) - considered to have largely controlled ragwort throughout New Zealand, with the weed populations reduced by 90-100% at some sites, except in the south and west of the South Island, where high rainfall favours ragwort but probably not the flea beetle, and in persistently intractable populations elsewhere.
Landcare Research (2016g) - some areas where the flea beetle had been released were almost clear of ragwort in as little as two years, and within about 10 years, in most drier climates around New Zealand where the beetle had been released, ragwort had pretty much disappeared.
Landcare Reasearch (2016h) - over 70 L. jacobaeae release sites nationwide revisited 20-30 years post-release and density of ragwort now compared to density at the time of release: at 42% of sites, no ragwort evident now; at 51% of sites it had declined 90-99%; at 7% of sites it had declined by 50% or less or even increased in density. Reductions of density occurred all over New Zealand, but the effect was strongest in the northern regions, consistent with previous information suggesting that ragwort declines were less dramatic in cooler or very wet regions, such as the West Coast and Southland. High numbers of the beetle were found at sites with mean annual rainfall up to 2000 mm.
Fowler et al. (2016) - the savings in ragwort control costs on dairy farms in New Zealand as a result of biocontrol by the flea beetle was predicted to be NZ$44 million for 2015 alone. These savings are now ongoing, with no further investment needed. A net present value analysis suggests that the New Zealand dairy sector is better off by more than $1.1 billion in net present value since 1926 (when ragwort biocontrol was first attempted, with other agents) from reduced control costs required for ragwort as a result of biocontrol by the ragwort flea beetle. This represents a benefit-to-cost ratio of 14:1, i.e. for every dollar invested in ragwort biocontrol New Zealand has gained $14 in reduced ragwort control costs. In addition, these savings are calculated only for the dairy sector, suggesting that if other livestock industries were taken into account savings would be even greater.
Gourlay (2021g) - Longitarsus jacobaeae has been highly successful in New Zealand. Typically, ragwort populations are substantially reduced within two to 10 years after the beetles have established and occasionally, it disappears altogether. However, L. jacobaeae has not been uniformly effective throughout New Zealand; spraying with herbicide can prevent the beetles from building up damaging populations and high rainfall also limits the effectiveness of the beetle. The ragwort plume moth ( Platyptilia isodactyla) has been introduced to control ragwort in high rainfall areas, such as the West Coast of the South Island.
Fowler et al. (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. Longitarsus jacobaeae, a root-boring beetle, does not have a New Zealand native ecological analogue and its impact in New Zealand is assessed as ‘heavy’. Unusually for weed biocontrol agents that have a significant impact on the target weed in New Zealand, L. jacobaeae has not been reported having damaging impacts in its native range. It is possible that such impacts in the native range have not been recognised because the impact of root feeders can be rather cryptic; it is also possible that, in the absence of parasitism, the population density of L. jacobaeae is much higher in New Zealand.
Impacts on non-targets:
Syrett (1985) - host range testing for L. jacobaeae was carried out in the laboratory against eight New Zealand native Senecio species, representing the four main native groups in this genus. No, or only slight, adult feeding and oviposition occurred in three of the groups, but higher levels were recorded on the two representatives of the erechtitoid group, particularly on S. wairauensis (feeding was approximately 50% of the rate recorded on S. jacobaea in no-choice tests and approximately 35% in multi-choice tests). However, beetles confined to S. wairauensis ceased ovipositing after a few days, and in larval feeding trials only one individual survived to adulthood on S. wairauensis. (No larvae survived on any other species except S. jacobaea.) Even if oviposition were to take place on S. wairauensis in the field, little larval development would be expected. Longitarsus jacobaeae appears to be highly specific to S. jacobaea and that it is extremely unlikely to be damaging to native New Zealand Senecio species.
Paynter et al. (2004) - surveys record no non-target feeding, despite laboratory tests predicting minor non-target impacts.
Paynter et al. (2015) - surveys of the potential non-target host, the native Senecio wairauensis (mountain fireweed), report no feeding.
References
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Fowler SV, Gourlay AH, Hill R. (2016). Biological control of ragwort in the New Zealand dairy sector: an ex-post economic analysis. New Zealand Journal of Agricultural Research 59(3): 205-215 https://www.tandfonline.com/doi/full/10.1080/00288233.2016.1170050
Fowler SV, Groenteman R, Paynter Q (2023). The highs and the lows: a cost benefit analysis of classical weed biocontrol in New Zealand. BioControl (2023) https://doi.org/10.1007/s10526-023-10225-2
Gourlay H (2007h). Ragwort flea beetle: Longitarsus jacobaeae. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Updated 2021 - see Gourlay (2021g)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/ragwort-flea-beetle/
Gourlay H (2021g). Ragwort flea beetle: Longitarsus jacobaeae. The Biological Control of Weeds Book - Te Whakapau Taru: A New Zealand Guide (Landcare Research) [Update of Gourlay (2007h)] https://www.landcareresearch.co.nz/discover-our-research/biodiversity-biosecurity/weed-biocontrol/projects-agents/biocontrol-agents/ragwort-flea-beetle/
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
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 (2016g). Farmer grateful for tiny beetle. Weed Biocontrol: What's New? 76: 8 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-76
Landcare Research (2016h). Comparing ragwort then with now: Part One. Weed Biocontrol: What's New? 77: 4-5 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-77
Landcare Research (2023h). The highs and lows of cost-benefit analyses. Weed Biocontrol: What's New? 106, August 2023 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/the-highs-and-lows-of-costbenefit-analyses/
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, Fowler SV, Gourlay AH, Peterson PG, Smith LA and Winks CJ (2015). Relative performance on test and target plants in laboratory tests predicts the risk of non-target attack in the field for arthropod weed biocontrol agents. Biological Control 80: 133-142 https://doi.org/10.1016/j.biocontrol.2014.10.007
Syrett P (1985). Host specificity of the ragwort flea beetle Longitarsus jacobaeae (Waterhouse) (Coleoptera:Chrysomelidae). New Zealand Journal of Zoology 12(3): 335-340 https://doi.org/10.1080/03014223.1985.10428287
Syrett P, Grindell JM, Hayes LM, Winks CJ (1991). Distribution and establishment of two biological control agents for ragwort in New Zealand. Proceedings of 44th New Zealand Weed and Pest Control Conference 44: 292-293
