Biological control of giant salvinia (Salvinia molesta) in a temperate region: cold tolerance and low temperature oviposition of Cyrtobagous salviniae

Success of Cyrtobagous salviniae Calder & Sands (Coleoptera: Curculionidae) for biological control of Salvinia molesta D. S. Mitchell in temperate regions has been less reliable than in tropical and subtropical regions and this difference is presumed to be due to greater winter mortality. We measured the cold tolerance of C. salviniae by comparing chill coma recovery time and survival of adults after exposure to freezing conditions among four geographic populations collected from Florida, Louisiana, Texas and Australia. Effects of winter temperature acclimation on low temperature oviposition also were determined. The Australian population was more cold tolerant than the three US populations. No oviposition by C. salviniae was observed at a water temperature of 17 °C and the oviposition rate at 19 °C was less than at 21, 23 and 25 °C. We suggest that introduction of cold tolerant strains of C. salviniae could increase its effectiveness in temperate regions of the US.