Soil characteristics in relation to the long-term efficacy of the biological control agent, the ragwort flea beetle (Longitarsus flavicornis (Coleoptera: Chrysomelidae)) in Australia

The root-feeding flea beetle, Longitarsus flavicornis, was released in Australia in 1979 for the biological control of ragwort, Senecio jacobaea. Although the agent has since become well established at many sites, its impact on ragwort populations is noted to vary between years, geographic locations, and under different land-management techniques. This paper addresses the possibility that these variations in efficacy are related to basic soil and climate features of the sites. Soil characteristics and climate were compared between sites where the flea beetle had controlled ragwort and sites where it has had minimal impact on ragwort populations. The only factors that varied significantly between successful and unsuccessful sites were salinity and the abundance of plant roots in the A1 soil horizon. Unsuccessful sites were found to have a higher average salinity and a lower abundance of plant roots compared to successful sites. Multivariate ordination revealed no pattern grouping successful and unsuccessful sites.