Aspects of thistle population dynamics with reference to Onopordum

W.J. Pettit, D.T. Briese and A. Walker, CSIRO Division of Entomology, Co-operative Research Centre for Weed Management Systems, GPO Box 1700, Canberra, ACT 2601, Australia.


An understanding of the population dynamics of the target weed is considered to be a key element in the evaluation of any biological control project. In the case of Onopordum thistles, data collection commenced prior to the release of agents and a set of data is now held on the demography of several infestations over a five-year period. This period covers climatic extremes of drought and high rainfall and provides a measure of the fluctuations in thistle population levels that occur in the absence of natural enemies. Such data will provide a basemark from which to measure the impact of future control strategies, including biological control. The study illustrates the type of data, such as seed bank estimates and survival between life stages, that will be important for the assessment of control strategies. The study also enables comparisons between populations of O. acanthium and those having an affinity to O. illyricum, the latter showing a greater tendency to perennation. Differences in life history traits will have implications for management of these thistles in particular, and other species of thistle in general.


Plant Protection Quarterly (1996) 11 (Supplement 2) 232-235.