Establishment and redistribution of <i>Longitarsus flavicornis</i> (Stephens) (Coleoptera: Chrysomelidae) for the biological control of ragwort (<i>Senecio jacobaea</i> L.) in Tasmania

Abstract

Abstract Ragwort flea beetle, Longitarsus flavicornis (Stephens), was first released as a biological control agent for ragwort in Tasmania in 1979. Field surveys to the end of February 1999 showed that it is now dispersed over all land known to be infested by ragwort in southern Tasmania, and over about 90% of the major infestations in the north. A redistribution program has been undertaken to accelerate spread of L. flavicornis by transferring field collected adults from established field sites during summer and autumn. Since 1986, almost 2 million adults have been distributed to 879 sites, with over 80% of transfers taking place between 1993 and 1999. A minimum of 1000 adults released/site resulted in establishment at 90% of the sites. Although large (&gt; 90%) reductions in ragwort densities have been recorded, we suspect that prevailing site conditions such as flooding and incompatible management practices such as use of boom‐sprayed herbicides, are restricting efficacy of L. flavicornis on many properties. Attempts to address this problem are now being made through use of integrated control strategies and establishment of complementary biological control agents.