Ecology and impact of invasive root weevils in a northern hardwood forest

A complex of invasive weevils has recently undergone a population eruption in the upper Great Lakes region. Adult and larval ecology is being examined in the Ottawa National Forest in the Upper Peninsula of Michigan. Adult weevils are folivores, feeding primarily on the leaf margins of sugar maple, ironwood, and raspberry. Weekly adult censuses indicated the presence of four species: Phyllobius oblongus, Polydrusus sericeus, Sciaphilis asperatus, and Barypeithes pellucidus. Phyllobius oblongus were the most common; weekly sweep net samples captured from 0 to 79 adults. Polydrusus sericeus was less common than P. oblongus, but still much more abundant than S. asperatus or B. pellucidus. Adult weevil populations peaked in June, and nearly all adults were gone by mid-July. Larvae are rhizophagous, and feed primarily on fine (i.e., <1 mm diameter) roots.  Significanly more larvae occur in the upper 15 cm of soil, which coincides with the greatest amount of fine root biomass. The highest larval mortality occurred in the spring. Studies are underway to determine the effects of larval and adult feeding on seedling growth and fine root dynamics in this northern hardwood ecosystem.