Oviposition of the ragwort flea beetle, Longitarsus flavicornis (Stephens) (Coleoptera: Chrysomelidae), in relation to the phenology of ragwort, Senecio jacobaea L. (Asteraceae)

Wick-wiping of herbicides in summer to kill flowering ragwort and reduce seed production is the current recommendation for the integration of herbicide use and biological control using Longitarsus flavicornis (Stephens) in Tasmania, Australia. Ragwort rosettes remain undamaged by wick-wiping and their survival provides a food source for L. flavicornis. This recommendation has always been based on the assumed negative impact of boom-sprayed herbicides on L. flavicornis without the availability of supporting data. Vacuum collections at a site at Franklin, Tasmania, showed that over 80% of adult L. flavicornis occurred on rosettes rather than on flowering plants. Glasshouse choice-trials of L. flavicornis oviposition behavior showed that over 95% of eggs were laid around rosettes rather than on flowering plants. These results now provide supporting evidence for the validity of the current integrated control strategy for ragwort. Reasons for the habitat preference by L. flavicornis of rosettes over flowering plants and the implications for the survival and increase of this biological control agent are discussed.