The Effect of Eurasian watermilfoil metal accumulation on the activity of milfoil weevil populations in Sudbury, Ontario
This paper explores patterns of metal accumulation in Eurasian watermilfoil (Myriophyllum spicatum), and determines whether populations of milfoil weevils (Euhrychiopsis lecontei) in the Sudbury region are visibly affected by these patterns. To investigate this relationship, milfoil patches in six Sudbury lakes, and one control lake (Baptiste Lake, near Bancroft, ON) were sampled for sediment and plant chemistry, as well as for milfoil weevil damage as a measure of weevil activity. Comparisons of sediment, milfoil root, and milfoil stem metal concentrations among the seven lakes found sediment metal concentrations of Cd, Cu, Ni, and Pb, were all lowest in the control lake, Baptiste. The greatest differences were found in Cu and Ni concentrations, which were approximately fifteen to eighty times higher in Sudbury. Milfoil metal concentrations in the root and stem were not strongly correlated to sediment concentrations indicating that total metal concentrations are not reflective of the available metal in the Sudbury Lakes. Weevil damage was weakly correlated with Cd/Zn ratios, but uncorrelated with all stem metal concentrations. Principal Components Analysis confirmed that metal accumulation in Eurasian milfoil could not predict milfoil weevil damage. It is unclear whether milfoil weevils are simply unaffected by metal contamination in their host plant, or whether the effect is too small to detect with this study design.