The weevil-watermilfoil interaction at different spatial scales: What we know and what we need to know

The North American weevil (Euhrychiopsis lecontei (Dietz)) is being conside red as a biological control agent for Eurasian watermilfoil (Myriophyllum s picatum L.). This native insect damages watermilfoil plants and is frequent ly associated with declining watermilfoil populations. Weevils and watermil foil interact over at least four different spatial scales-1) the level of t he individual plant, 2) the level of beds within lakes, 3) lakes within geo graphic regions and 4) geographic regions-and we still have much to learn a bout the interaction at these different scales. For example, at the level o f the individual plant, we have a good idea of how weevil herbivory influen ces plant growth but we still need to determine whether or not weevils can cause plant death. At the level of beds, we do not know ho cv long it takes a weevil population to reach a density that will result in a significant r eduction in watermilfoil biomass. Finally, at the level of lakes within geo graphic regions, we do not know if differences in lake productivity influen ce the weevil-watermilfoil interaction. It is my hope that addressing these questions and filling in the gaps in our knowledge will lead to a better u nderstanding of the interactions between these two species and to more effi cient use of the insect in watermilfoil control projects.