Hitting the beech: Evidence for substantial host range contraction following the invasion of an exotic, polyphagous beetle
The introduction of alien pest insects can have substantial impacts on indigenous ecosystems. One of the key components driving the success of their establishment is host suitability within the invaded range. For example, the establishment of the exotic beech leaf-mining weevil, Orchestes fagi L., on American beech, Fagus grandifolia (Ehrh.), in Nova Scotia is likely due in part to its use of beech, Fagus sylvatica L., as a host throughout its native European range. However, evidence that O. fagi feeds on several additional plants in Europe suggests that its North American host range should extend beyond a single species. To determine whether additional plant species co-occurring with beech are susceptible to weevil damage, we employed a combination of observational studies and no-choice feeding assays to assess adult feeding on a variety of potential hosts (including beech) within its introduced range.
Contrary to our prediction, and to reports of its behavior in Europe, adult beech weevil feeding damage was almost entirely exclusive to beech, a trend that was consistent across observational and manipulative feeding assays. Moreover, adults that emerged in the summer (i.e., offspring of the overwintered generation) consumed no plant material at all, which is a departure from normal life history patterns observed in its native range. Overall, we anticipate that this restricted feeding breadth is likely to result from either nutritional inequality or host phenological asynchrony with indigenous plants other than beech. Although weevils have been observed to use secondary hosts in other capacities such as overwintering sites, its complete dependence on beech as a food resource suggests that impacts on secondary hosts will be extremely minimal.