Feedback between invasive belowground herbivores and habitat composition in northern hardwood ecosystems

A complex of invasive root feeding weevils has recently undergone a population eruption in the upper Great Lakes region. Adult emergence peaked in early June, with adults of the various weevil species emerging at different times depending on their larval host plant. Weekly censuses indicated differential temporal patterns of host utilization. Sugar maple was utilized most heavily in early spring, but adults became increasingly concentrated on ironwood and raspberry as the season progressed. We conducted field and laboratory assays to evaluate the effects of host utilization patterns. In the field, Phyllobius oblongus adult emergence was as high in patches of the late-season hosts, ironwood and raspberry, as it was in the early-season host, sugar maple. Emergence of Polydrusus sericeus was substantially higher from ironwood and raspberry than sugar maple. Laboratory assays were used to compare adult longevity and fecundity on sugar maple, ironwood, and raspberry. Host plant had minimal effect on adult longevity, but egg production of both weevils was significantly greater when fed raspberry than ironwood or sugar maple. Likewise, both species produced more eggs when fed on ironwood than sugar maple. These results have implications to three general areas of invasion ecology: the intersection of belowground herbivory and exotic insects; the impacts of and interactions among multiple invasive insect species; and the effects of forest management practices on invasive herbivores. Specifically, practices such as logging, road construction, and natural processes such as gap formation may indirectly benefit invasive weevil populations due to positive effects of disturbance on raspberry.