Authors: Laura L. Jester1, Michael A. Bozek1, Daniel R. Helsel2, & Sallie P. Sheldon3
1Wisconsin Cooperative Fishery Research Unit 4, College of Natural Resources, UW—Stevens Point, Stevens Point, WI 54481.
2Wisconsin Department of Natural Resources, 101 S. Webster St., Madison, WI 53703.
3Middlebury College, Department of Biology, Middlebury, VT 05753.
Journal: J. Aquat. Plant Manage. 38: 2000.
Abstract: The specialist aquatic herbivore Euhrychiopsis lecontei (Dietz) is currently being researched as a potential biological control agent for Eurasian watermilfoil (Myriophyllum spicatum L.). Our research in Wisconsin focused on 1) determining milfoil weevil distribution across lakes, 2) assessing limnological characteristics associated with their abundance, and 3) evaluating milfoil weevil augmentation as a practical management tool for controlling Eurasian watermilfoil. The geographic distribution of the milfoil weevil is widespread with 49 new records of the weevil among Wisconsin lakes containing Eurasian watermilfoil. Among 31 of the Wisconsin lakes that contained the milfoil weevil, their abundance varied from non-detectable to 2.5 weevils per stem of Eurasian watermilfoil. No whole-lake characteristics and only some milfoil bed characteristics such as the percentage of natural shoreline, the depth and distance of the Eurasian watermilfoil bed from shore, the number of apical tips and the percentage of broken apical tips per stem of Eurasian watermilfoil, were significantly correlated with milfoil weevil abundance. Twelve Wisconsin lakes augmented with one of three different treatment levels of weevils (1, 2 or 4 weevils per Eurasian watermilfoil stem) showed some significant damage to the Eurasian watermilfoil in small study plots at the end of the first treatment season. Additional sampling to assess long-term effects of this augmentation is ongoing.