Herbivory influences the dispersal and colonization of Cyrtobagous salviniae: Implications for biological control

Native to Brazil, the invasive aquatic fern Salvinia molesta Mitchell, Salviniaceae (giant salvinia) has invaded freshwater ecosystems in south Louisiana where it hinders crucial ecosystem services. First introduced in 1999, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae; salvinia weevil) became a successful host-specific biological control agent for S. molesta. The goal of this study was to understand how plant quality influences C. salviniae dispersal. We hypothesized that an increase in localized herbivory would promote dispersal from a release point. One end of an outdoor pond with 100%  coverage of S. molesta was inoculated with C. salviniae infested S. molesta. To track C. salviniae flight, sticky traps were placed at various heights (0.1, 0.5, 1, and 2 m) and arranged on equidistant sampling stations (n=10) throughout the pond.  Sticky traps were deployed every two weeks for 24 hours, and counts of  C. salviniae on the sticky traps was measured. Analyses of plant chemistry and nutrient content occurred at the beginning, middle, and end of the study.  Additional parameters including S.molesta plant health, percent coverage, biomass, Normalized Difference Vegetation Index (NDVI), and C. salviniae densities were recorded monthly at each sampling station (n=10). Outcomes of this study would improve our understanding of C. salviniae flight and the role of plant quality on adult dispersal. Weevil release recommendations for land managers will be improved based on the outcomes of this study.