Ecology and impact of a complex of invasive root-feeding weevils in a northern hardwood forest.

摘要

I examined adult feeding behavior, larval overwintering biology, and field abundance patterns and impact of a complex of invasive root-feeding weevils on a population of sugar maple seedlings in a northern hardwood forest. Phyllobius oblongus, Polydrusus sericeus, Barypeithes pellucidus, and Sciaphilus asperatus are the most common species. Adults are folivorous on several plant species. Larvae are rhizophagous, and overwinter belowground.;Polydrusus sericeus lived longer on sugar maple ( Acer saccharum), ironwood (Ostrya virginiana), basswood (Tilila americana), and raspberry (Rubus spp.), than P. oblongus in no-choice assays, but P. oblongus had a higher leaf consumption rate on sugar maple. Eastern leatherwood (Dirca palustris), was not a suitable host for either weevil species. Phyllobius oblongus preferred newly flushed sugar maple compared with older sugar maple and raspberry. Adult P. oblongus showed less pronounced performance or feeding preferences later in the growing season.;Larval supercooling points for B. pellucidus, P. oblongus, and P. sericeus were lower than temperatures normally encountered, and larval cold tolerance increased over the winter in all species. Larval hemolymph showed some antifreeze protein or glycolipid properties. These data suggest that in this thermally-buffered environment these larvae employ a behavioral freeze avoidance mechanism to survive the winter.;Phyllobius oblongus, P. sericeus, B. pellucidus, and S. asperatus emerged in early to mid June each year, and populations were highly variable within and among seasons. Each weevil species was captured with different efficacy by emergence traps or sweep netting. These results suggest that the broad feeding ranges of these invasive weevils could contribute to their ability to contend with highly variable environmental conditions often encountered in this ecosystem.;The sugar maple seedling community had a high natural mortality rate (over 85%) as indicated by tagged seedlings monitored continuously throughout the study. Heavy defoliation on a single seedling often led to mortality. Effects of adult or larval weevils on sugar maple seedling community dynamics were sporadic, and patterns were difficult to discern. Overall, while some individuals are killed as a result of adult weevil defoliation, the sugar maple seedling community as a whole is dynamic enough to tolerate herbivory by this suite of weevils.