Cold Tolerance and Overwintering Physiology of the Salvinia Weevil (Cyrtobagous salviniae): Improving the Biological Control of Giant Salvinia in Temperate Louisiana
Master of Science (MS)
Cyrtobagous salviniae is widely used for biological control of Salvinia molesta. Despite success in tropical and subtropical regions, the effectiveness of C. salviniae on S. molesta is inconsistent in temperate regions, indicating the need for a better understanding of the thermal biology of this agent. The objectives of this study were to compare cold tolerance of C. salviniae populations from the temperate native range and Louisiana, and characterize the overwintering physiology and population dynamics of C. salviniae in Louisiana. Surveys of the Lower Paraná-Uruguay Delta resulted in the first record of C. salviniae in Uruguay, and revealed the most southern distribution of this species in Argentina and Uruguay. Survival at 0°C was 1.5-times greater, chill coma recovery time was 1.8-times faster, and SCP was 1.2-times lower in the Argentine population compared to the Louisiana population. These findings show that the Argentine provenance should be considered for managing S. molesta in temperate regions. Besides host range tests, cross breeding between the Louisiana and Argentine populations should be investigated to determine the life histories of any possible hybrid. Laboratory assays demonstrated phenotypic plasticity in the cold tolerance of populations from central and southern Louisiana when acclimated to winter conditions. Survival at 0°C was 1.8- and 1.7-times greater, critical thermal minimum was 1.2- and 1.3-times lower, and chill coma recovery time was 2.7- and 1.5-times faster in the winter treatments compared to summer treatments, for both populations (central and south, respectively). Seasonal changes in reproductive status, fat body, and water content were evident from the field study, and are speculated to contribute to the overwintering success of adults at both sites. Adult and larval densities showed that populations were most vulnerable in the late winter/early spring, presumably when water temperatures and host plant quality have not yet recovered. Seasonal monitoring of the physiological status and population dynamics should be conducted to improve the timing of releases and predicting the success of S. molesta control. In conclusion, the management of S. molesta in northern Louisiana should incorporate releases of cold tolerant populations, and seasonal monitoring of physiology and population dynamics of C. salviniae.
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Russell, Alana D., "Cold Tolerance and Overwintering Physiology of the Salvinia Weevil (Cyrtobagous salviniae): Improving the Biological Control of Giant Salvinia in Temperate Louisiana" (2017). LSU Master's Theses. 4421.