Thermal tolerance of Cyrtobagous salviniae: a biocontrol agent in a changing world

The weevil Cyrtobagous salviniae Calder & Sands 1985 (Family: Curculionidae) is a highly effective biocontrol agent for the invasive water fern Salvinia molesta D.S. Mitchell (Family: Salviniaceae). The life histories of both organisms are affected by temperature, making the potential impacts of climate change on efficacy of control an important area in which comprehensive understanding is required. Here we use warming tolerance (WT) and low temperature tolerance (LTT) as measures of C. salviniae’s sensitivity to climate warming, calculated across South Africa using critical thermal limits, lethal temperature limits and mean maximum (Tmax) and minimum (Tmin) environmental temperatures under present climatic conditions and two future periods (2040s and 2080s). From the present climate to the 2080s the WTs of C. salviniae decrease and LTTs increase indicating C. salviniae may face greater constraints on survival as Tmax nears the upper thermal limits, but increased population persistence over cool months as Tmin increases.