Ecological research on Senecio species and their natural enemies

Written by Jon Sullivan, Bio-Protection and Ecology Division, Lincoln University

Last modified: 26 October 2006

The website is currently under construction. Check back soon for a lot more information!

Senecio: one genus to rule them all.

Senecio (Asteraceae) is one of the world's largest genera of plants, containing a diverse and unruly rabble of about 1500 species of different functional types, from desert suculents to vines. Some of the weirdest taxa have been pruned off into their own genera or are in the process being pruned. As examples, the New Zealand tree daisies in the genus Brachyglottis were originally included in Senecio and the Cape Ivy, a native vine of southern Africa and invasive in many other countries, was until recently known as Senecio mikanioides and is now Delairea odorata.

Most core Senecio species are short-lived herbaceous plants, making them amenable to experimental ecological research. Being short-lived, their populations can also be responsive to environmental changes such as the invasion of exotic plants and insect herbivores, again making them excellent subjects for ecological study.

Senecio in New Zealand: an excellent ecological study system.

The New Zealand flora includes 37 wild Senecio species, including 13 endemics, 6 native non-endemics, and 14 fully naturalised exotic species (see Table 1 for the full species list). Amongst the naturalised species is the poisonous ragwort, S. jacobaea, the bane of sheep and cattle farmers and the subject of an ongoing biological control programme. Together with collaborators Simon Fowler and Chris Winks at Landcare Research, and others, I have been focusing my ecological research increasingly on this group of species and the insect herbivore (and pathogen) food web associated with them.

The following are the main research questions we are answering with the New Zealand Senecio study system, all loosely based around the general question of how do food webs affect plant ecology in an invaded world (particularly the details of enemy release and biotic resistance in action).

  1. To what degree are plant geographic range limits structured by the actions of host-specialised natural enemies?
  2. How do the food webs created by the biological control of weeds directly and indirectly affect associated native food webs?
  3. To what extent do native/endemic monophagous insect herbivores provide biotic resistance to the naturalisation and invasiveness of naturalised congeners of native plants?
  4. What roles do competition from congeneric naturalised plant species and attack by naturalised insect herbivores play in the decline in abundance and distribution of so many New Zealand endemic herbs?
  5. To what degree can monophagous insect herbivores associated with endemic forest and scrubland plants successfully associate with congeneric naturalised plant species and spread into more strongly modified rural and urban environments (and thereby avoid declining with their native host plants)? (How general are observed New Zealand patterns, for example by Kuschel's 15-year beetle study in suburban Auckland, of endemic monphagous insects being as much forest haitat specialists as host specialists?)

Senecio natural enemies.

For five years now we have been building up a picture of the natural enemy food web based on native and naturalised New Zealand Senecio species. The first two scientific papers from the first phases of this work are now in preparation. One is on the effects of protection from natural enemies on the capability of Senecio species to grow beyond their natural range limits. The second is on the extent to which native monophagous Senecio herbivores have expanded their host ranges onto naturalised Senecio species, especially in landscapes where their native hosts are rare or absent.

More about Senecio in New Zealand

Visit the New Zealand Plant Names database at nzflora.landcareresearch.co.nz for an current list of the Senecio taxa in New Zealand and their biostatus.

Volume IV (1989) of the New Zealand Flora contains an excellent botanical key and descriptions of most New Zealand Senecio species, both native and naturalised.

Drury, D. G. 1974. Illustrated and annotated key to the erechtitoid Senecios in New Zealand (Senecioneae - Compositae) with a description of Senecio diaschides. New Zealand Journal of Botany, 12:513–540
Drury's classic paper remains a useful guide to New Zealand Senecio species and contains outstanding line drawings by Keith West.

More about Senecio natural enemies

View/download a preliminary list of insect and fungal natural enemies reared from or collected on New Zealand Senecio species.

ragwort and magpie moth

The invasive weed ragwort, Senecio jacobaea, and a caterpillar of the endemic magpie moth, Nyctemera annulata, a Senecio specialist herbivore that now largely depends on naturalised plants in many New Zealand rural and urban landscapes. Nyctemera annulata now faces competition and hybridisation with the recently naturalised Asutralia N. amica in northern New Zealand. Senecio jacobaea has had three biological control insects introduced against it and a further two agents are in the process of release.

Useful Senecio References

  • Ahmed, M., and Wardle, D. A. 1994. Allelopathic potential of vegetative and flowering ragwort (Senecio jacobaea L.) plants against associated pasture species. Plant and Soil, 164:61–68.
  • Betteridge, K., McGregor, P. G., Costall, D. A., and Peterson, P. G. 2000. Biological control of ragwort - does sheep grazing affect ragwort flea beetle? New Zealand Plant Protection, 53:54–58.
  • Crawley, M. J., and Gillman, M. P. 1989. Population dynamics of cinnabar moth and ragwort in grassland. Journal of Animal Ecology, 58:1035–1050.
  • Drury, D. G. 1974. Illustrated and annotated key to the erechtitoid Senecios in New Zealand (Senecioneae - Compositae) with a description of Senecio diaschides. New Zealand Journal of Botany, 12:513–540.
  • Dymock, J. J. 1987. Population changes of the seedfly, Pegohylemyia jacobaeae (Diptera: Anthomyiidae) introduced for biological control of ragwort. New Zealand Journal of Zoology, 14:337–342 .
  • Fenner, M., and Lee, W. G. 2001. Lack of pre-dispersal seed predators in introduced Asteraceae in New Zealand. New Zealand Journal of Ecology, 25:95–99.
  • McEvoy, P. B., Rudd, N. T., Cox, C. S., and Huso, M. 1993. Disturbance, competition, and herbivory effects on ragwort Senecio jacobaea populations. Ecological Monographs, 63:55–75.
  • Poole, A. L., and Cairns, D. 1940. Botanical aspects of ragwort (Senecio jacobaea L.) control. Department of Scientific and Industrial Research Bulletin 82, DSIR, Wellington.
  • Spiller, D. M., and Wise, K. A. J. 1982. A catalogue (1860-1960) of New Zealand insects and their host plants. Department of Scientific and Industrial Research Bulletin 231, DSIR, Wellington.
  • Syrett, P. 1985. Host specificity of the ragwort flea beetle Longitarsus jacobaeae (Waterhouse) (Coleoptera: Chrysomelidae). New Zealand Journal of Zoology, 12:335–340.
  • Syrett, P., Grindell, J. M., Hayes, L. M., and Winks, C. J. 1991. Distribution and establishment of two biological control agents for ragwort in New Zealand. Proceedings of the fourty-fourth New Zealand Weed and Pest Control Conference, pp. 292-295.
  • Syrett, P., Scheele, S. M., and Philip, B. A. 1984. Renewed activities in biological control of ragwort. Proceedings of the thirty-seventh New Zealand Weed and Pest Control Conference, pp. 37-41.
  • Thompson, A. 1985. Population studies on ragwort (Senecio jacobaea). Proceedings of the thirty-eighth New Zealand Weed and Pest Control Conference, pp. 122-126.
  • Thompson, A., and Makepeace, W. 1983. Longevity of buried ragwort (Senecio jacobaea L.) seed. New Zealand Journal of Experimental Agriculture, 11:89–90.
  • Wardle, D. 1987. The ecology of ragwort (Senecio jacobaea L.) - a review. New Zealand Journal of Ecology, 10:67–76.
  • Wilson, J. B., Rapson, G. L., Sykes, M. T., Watkins, A. J., and Williams, P. A. 1992. Distributions and climatic correlations of some exotic species along roadsides in South Island, New Zealand. Journal of Biogeography, 19:183–193.
  • Wardle, D. A., Nicholson, K. S., and Rahman, A. 1995. Ecological effects of the invasive weed species Senecio jacobaea L.(ragwort) in a New Zealand pasture. Agriculture Ecosystems & Environment, 56:19–28.
  • Webb, C. J. 1987. Checklist of dicotyledons naturalised in New Zealand.18. Asteraceae (Compositae) subfamily Asteroideae. New Zealand Journal of Botany, 25:489–501.
  • Windig, J. J., and Vrieling, K. 1996. Biology and ecology Longitarsus jacobaeae and other Longitarsus species feeding on Senecio jacobaea. In P. H. A. Jolivet, and M. L. Cox (eds.), Chrysomelidae biology, Vol. 3. General studies., pp. 315–326. SPB Acdemic Publishing, Amsterdam.