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
Released:
1983-1986, early 1990's
Release details:
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 (2007e) - 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 (2007e) - 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 (2007e) - 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.
Impacts on non-targets:
Paynter et al. (2004) - surveys record no non-target feeding, despite lab tests predicting minor non-target impacts.
Paynter et al. (2015) - surveys of 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
Gourlay H. (2007e). Ragwort Flea Beetle. In The Biological Control of Weeds Book (Landcare Research) https://www.landcareresearch.co.nz/discover-our-research/biosecurity/weed-management/using-biocontrol/the-biological-control-of-weeds-book/
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. http://www.landcareresearch.co.nz/resources/collections/nzac/holdings/biological-control-voucher-collection
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
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
Paynter, Q.E., Fowler, A.H., Gourlay, M.L., Haines, M.L., Harman, H.M., Hona, S.R., Peterson, P.G., Smith, L.A., Wilson-Davey, J.R.A., Winks, C.J. and Withers, T.M. (2004). Safety in New Zealand weed biocontrol: A nationwide survey for impacts on non-target plants. New Zealand Plant Protection 57: 102-107
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
