Evaluation of Winter Management Methods to Enhance Survival of the Giant Salvinia Weevil, Cyrtobagous salviniae
Semester of Graduation
Master of Science (MS)
Giant salvinia (Salvinia molesta Mitchell) is a noxious aquatic weed in the southeastern United States. Dense plant mats create ecological and economic consequences by displacing native species and impacting freshwater industries. Biological control programs using the salvinia weevil (Cyrtobagous salviniae Calder and Sands, Coleoptera: Curculionidae) have limited efficacy in giant salvinia’s northernmost range due to the weevil’s low cold tolerance and long-term establishment rates. Spunbonded polypropylene (SBP) fabrics and manipulation of plant density were evaluated as two strategies for managing giant salvinia mats during winter. Greenhouse, laboratory, and field experiments were conducted to determine the suitability of these strategies for enhancing salvinia weevil survival and establishment in Louisiana. Plant quality, weevil survival, and mat temperatures were evaluated for plants that were either covered with insulating fabrics or artificially crowded to low, medium, and high densities. Spunbonded polypropylene fabrics raised mat temperatures by 0.3 to 3.5°C and decreased adult weevil mortality by 36 to 66% in laboratory and field studies in south LA. In simulated cold fronts, SBP covers reduced plant damage by 1.8- to 4.8-times compared with uncovered controls. High density plant mats raised water column temperatures by 0.6 to 1.9°C compared to open water and by 0.6 to 1.0°C compared to low density plant mats. High density plant mats experienced 15% greater adult weevil mortality than medium density plant mats in laboratory experiments at -7°C. Field overwinter survival did not differ among treatments in north and central LA, but in south LA adult and larval population density were 2.2- and 8.3-times greater, respectively, in high density treatments than in low density treatments. Artificial refugia made from SBP are a low-cost alternative to greenhouse films for managing water temperature and are well suited for outdoor mass-rearing operations. Managing plant density is a potentially useful management strategy for salvinia weevil release sites with mild winter cold exposure. Continued evaluation is recommended to assess the suitability of these refugia for giant salvinia and other weed biological control programs during severe winters in temperate climates.
Moshman, Lori Robyn, "Evaluation of Winter Management Methods to Enhance Survival of the Giant Salvinia Weevil, Cyrtobagous salviniae" (2017). LSU Master's Theses. 4330.