Surveys in Argentina and Uruguay reveal Cyrtobagous salviniae (Coleoptera: Curculionidae) populations adapted to survive temperate climates in southeastern USA

Authors: RUSSELL, ALANA - Louisiana State University; JOHNSON, SETH - Louisiana State University; XIMENA, CIBILS - National Agricultural Research Institute(INIA); MCKAY, FERNANDO - Fuedei; MOSHMAN, LORI - Louisiana State University; Madeira, Paul; Blair, Zizah-Wossen; DIAZ, RODRIGO - Louisiana State University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2017
Publication Date: 4/1/2017
Citation: Russell, A., Johnson, S., Ximena, C., McKay, F., Moshman, L., Madeira, P.T., Blair, Z.J., Diaz, R. 2017. Surveys in Argentina and Uruguay reveal Cyrtobagous salviniae (Coleoptera: Curculionidae) populations adapted to survive temperate climates in southeastern USA. Biological Control. 107:41-49.

Interpretive Summary: Cyrtobagous salviniae is a weevil used in the United States, South Africa, Australia and other countries to biologically control the exotic and invasive weed Salvinia molesta. The weevil has shown success in controlling Salvinia in tropical and subtropical regions. In more temperate regions, however, its establishment has been inconsistent. We attempt here to find native populations in temperate regions which are adapted to survive freezing winter temperatures. We first determined climatically similar regions in South America to temperate Louisiana. We then searched these regions for new populations of C. salviniae. We also looked at the phylogenetic (family) relationships using DNA sequencing among C. salviniae populations from Louisiana, U.S. and the Paraná-Uruguay Delta, South America. Next, we compared the cold tolerance of the different populations of C. salviniae. Exploration of the Lower Paraná-Uruguay Delta region revealed what is likely the most southern distribution of C. salviniae in Argentina and Uruguay. Phylogenetic identification of this species indicated that it is a different biotype than the Brazilian biotype first released worldwide but likely the same species. Analysis of the climate in Louisiana revealed colder temperatures and more frequent cold fronts in the north, leading to winter population crashes. This suggested identifying more cold tolerant C. salviniae populations would improve the management of S. molesta in temperate regions. The cold tolerance of C. salviniae populations from Louisiana (LA) and Argentina (AR) were evaluated by comparing survival at 0°C, chill coma recovery times (time until recovery of muscle function), and supercooling points (the temperature below which an insect is unable to stop itself freezing despite the chemicals in its body). The survival at 0°C was 1.5-times greater, the mean chill coma recovery time was 1.8-times faster, and the mean SCP was 1.2-times lower in the Argentine population compared to the Louisiana population. This suggests that the Argentine population is more cold tolerant and should be further evaluated as a management tool of S. molesta in temperate regions. Further research should be conducted to prove the insect feeding and reproduction is specific to C. salviniae. Cross breeding of the Louisiana and Argentina/Uruguay populations should also be conducted to determine the possibility of hybridization.

Technical Abstract: Cyrtobagous salviniae is widely used in several countries, including the United States, South Africa and Australia, for the biological control of Salvinia molesta. Despite success in tropical and subtropical regions, C. salviniae establishment is inconsistent in temperate regions, and therefore populations adapted to survive freezing winter temperatures are needed. The objectives of this study were to determine the regions of South America that are climatically similar to Salvinia habitats in temperate Louisiana, conduct explorations to these regions to search for new populations of C. salviniae, establish the phylogenetic relationships among C. salviniae populations, and compare the cold tolerance of populations of C. salviniae from Louisiana, US and the Paraná-Uruguay Delta, South America. Foreign exploration of the Lower Paraná-Uruguay Delta region resulted in the first record of C. salviniae in Uruguay, and likely revealed the most southern distribution of this species in Argentina and Uruguay. Phylogenetic identification of this species indicated that it is a different biotype than the Brazilian biotype first released in the United States in 2001. Analysis of the climate in south, central, and north Louisiana revealed colder and more frequent cold fronts in the north, leading to winter population crashes. Regional differences in Louisiana thermal regimes suggest the need for region specific management plans, such as the implementation of cold tolerant C. salviniae populations in the management of S. molesta in temperate regions. The cold tolerance of C. salviniae populations from Louisiana (LA) and Argentina (AR) were evaluated by comparing survival at 0°C, chill coma recovery times, and supercooling points (SCP). The survival at 0°C was 1.5-times greater (Lt90 AR: 11.4 d vs. Lt90 LA: 7.7 d), the mean chill coma recovery time was 1.8-times faster (AR: 5.0 min vs. LA: 8.8 min), and the mean SCP was 1.2-times lower (AR: -16.3°C vs. LA: -13.5°C) in the Argentine population compared to the Louisiana population, respectively. Findings from this study suggest that the Argentine population is more cold tolerant than the Louisiana population, and should be further evaluated as a tool for managing S. molesta in temperate regions. We suggest that further research should be conducted on the host range and cross breeding of the Louisiana and Argentina/Uruguay populations of C. salviniae to determine the possibility of hybridization and subsequent impacts on life histories.