Performance of <i>Salvinia molesta</i> (Salviniae: Salviniaceae) and its biological control agent <i>Cyrtobagous salviniae</i> (Coleoptera: Curculionidae) in freshwater and saline environments

Abstract Giant salvinia ( Salvinia molesta Mitchell; Salviniaceae) is an invasive aquatic fern that inflicts significant economic and ecological threats when unmanaged. Biological control of giant salvinia using the semi-aquatic weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), has proven successful in tropical and subtropical regions. The study aimed to assess the impact of salinity on S. molesta growth and health, as well as C. salviniae feeding behavior and density. Laboratory and outdoor mesocosm experiments were conducted at three salinity levels, &lt;1, 5, and 10 ppt, alongside a field survey in southwestern Louisiana. Results indicated that S. molesta growth and health declined with increasing salinity, with significant damage observed at 5 ppt and near-total mortality at 10 ppt. C. salviniae feeding showed no significant differences across salinity levels in controlled settings, but field data revealed a decrease in weevil density at higher salinities. These findings suggest that while S. molesta can tolerate moderate salinity, its biological control via C. salviniae is less effective in saline environments. The study underscores the need for adaptive management strategies in coastal regions facing rising salinity due to climate change and sea-level rise.