Location: Invasive Plant Research LaboratoryTitle: Weevils versus no weevils: a comparison of Salvinia minima populations in Florida and Louisiana Author
Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2012
Publication Date: 9/30/2012
Citation: Tipping, P.W., Martin, M., Center, T.D. 2012. Weevils versus no weevils: a comparison of Salvinia minima populations in Florida and Louisiana. Florida Entomologist. 95(3):779-782. Interpretive Summary: Although the range of common salvinia in the U.S. includes Florida and Louisiana, the plant behaves differently between states, most notably in Louisiana where it is considered a significant aquatic weed. Plant and insect populations were sampled 11 times in both states over consecutive weeks during 2002 through 2004. Common salvinia biomass was more than twice as high in Louisiana as compared to Florida. Plant coverage was also greater and plants were healthier in Louisiana. Although air temperature was greater in Louisiana, water temperature was the same between sites. The most unequivocal difference between states was the absence of the weevil Cyrtobagous salviniae in Louisiana. This specialist herbivore has repeatedly demonstrated its ability to suppress common and giant salvinia and is probably the reason why the weed status of the plant differs between the states.
Technical Abstract: Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) is a successful biological control agents of aquatic weeds including common salvinia, Salvinia minima. Although S. minima has caused significant problems in Louisiana, it rarely forms persistent mats in Florida, perhaps because of the presence of C. salviniae in Florida but not Louisiana. The goal of this study was to compare population variables of S. minima between two similar but distant areas that differed primarily in the presence or absence of C. salviniae. Environmental, plant, and insect variables were compared between field sites in Florida and Louisiana during 2002 through 2005. Sites were located in selected natural areas in south Florida and in Jean Lafitte National Park and Preserve near New Orleans, Louisiana. Eleven samples were chosen for comparison because sampling was conducted between states in consecutive weeks. The Louisiana sites contained more than twice as much S. minima biomass as their Florida counterparts. Plant coverage was also greater in Louisiana with a higher percentage of green or ‘healthier’ plants compared to Florida. Overall plant quality, based on CN ratios, was not different between states. Population patterns of S. minima between states were strikingly different with Louisiana populations exhibiting regular cycles with peaks during warmer months, while Florida populations lacked any distinct cycles. An average of 15.7 C. salviniae was recorded per square meter in Florida versus none in Louisiana. As the ability of C. salviniae to regulate S. minima has been well documented, we submit that its absence in Louisiana largely explains the differences in S. minima population parameters compared to Florida.