Impact of climate change on biocontrol of weeds: Paterson's curse as a model

As a first step in assessing the potential impact of climate change on biological control of weeds by insects, we undertook a survey across a large geographical range in New South Wales and Victoria to sample the exotic weed Paterson’s curse and the major insect biocontrols released for its management. Occurrence data for the biocontrols were analysed to assess their spread from known release sites, and plant tissues were analysed for the presence of pyrrolizidine alkaloids in the leaves and naphthoquinones in the roots. The biocontrols showed variable spread from sites of introduction, and their abundance was unrelated to the levels of secondary chemicals. Alkaloids tended to decrease with distance from the equator, and naphthoquinones were highest in the warmest, driest portions of the survey area. The results suggest that warmer, drier weather may not impact the ability of biocontrol agents to suppress populations of Paterson’s curse, but the increase of pyrrolizidine alkaloids with temperature may exacerbate adverse effects of the weed on livestock feeding in pastures infested with it.