Efficacy and plant finding behavior of Euhrychiopsis lecontei Dietz (Coleoptera: Curculionidae), a biological control agent for Eurasian watermilfoil

Euhryciopsis lecontei (Dietz) is a native aquatic weevil that specializes on aquatic plants in the genus Myriophyllum (milfoils). As such, it has been used as a biological control agent for Eurasian watermilfoil (Myriophyllum spicatum), a troublesome invasive aquatic macrophyte. Data collect by EnviroScience, Inc. (Stow, OH) regarding E. lecontei stocking for control of Eurasian watermilfoil in 30 Michigan and Wisconsin lakes were analyzed to characterize efficacy of weevil control. There was substantive variability in weevil efficacy that remained largely unexplained by the dataset. However, there was at least some evidence that the weevils may be working, as final plant densities significantly lowered with time between initial and final surveys at treatment sites but not controls. Plant senescence may have confounded interpretation of the data, however, so better methods of data collection are suggested to get around the problems of plant senescence and other factors that may have confounded the data. Though variability in weevil efficacy may still be unexplained, one factor that may influence weevil efficacy is plant finding behavior. Through multiple behavioral experiments, we showed that weevils use vision to at least initially find their host-plants. Weevils could only find plants in the light, were still attracted to plants that were sealed in vials to prevent detection of any plant chemicals, and were even attracted to plants in turbid water. Weevils may even be able to visually differentiate plant species. This may be the first report of an aquatic specialist using vision to detect host-plants.