Competitive interaction of Salvinia molesta (Salviniaceae) and Oxycaryum cubense (Cyperaceae) and the impact on the biological control agent, Cyrtobagous salviniae (Curculionidae)

Salvinia molesta is an invasive aquatic fern native to Brazil that impedes critical ecosystem services. Cyrtobagous salviniae is a host-specific weevil native to Brazil that has been successful at reducing S. molesta coverage in subtropical and tropical regions. While monitoring C. salviniae survey sites and rearing ponds across Louisiana, the emergence of a secondary invasive weed, Oxycaryum cubense, has been observed. Oxycaryum cubense is a floating, epiphytic perennial sedge that is native to South America and the West Indies. Due to the reproductive characteristics of O. cubense, it can quickly form a tussock and rapidly establish within an existing mat of S. molesta. However, little is known about the interaction between these two aquatic weeds. This study aims to understand the competitive interaction between S. molesta and O. cubense and whether this interaction impedes the population growth of C. salviniae. A factorial mesocosm design was used to evaluate the competitive interactions. The treatment levels are five S. molesta:O. cubense percentage matrices with presence or absence of C. salviniae and presence or absence of nutrients. Plant performance (biomass, stem height, number of new shoots, histol thickness, presence of inflorescence, percent coverage, percent green, plant stage, root/rhizome length) and C. salviniae population density were measured overtime for each treatment. Results of this study will be discussed in the context of management strategies for the biological control program for S. molesta in Louisiana.