Spillover of a biological control agent (Chrysolina quadrigemina) onto native St. Johnswort (Hypericum punctatum)

Abstract

Biological control agents may have unintended effects on native biota, particularly species that are closely related to the target invader. Here, we explored howChrysolina quadrigemina, a beetle introduced to control the invasive weedHypericum perforatum, impacts nativeH. punctatumin Tompkins County, New York, USA. Using a suite of complementary field surveys and experimental manipulations, we examined beetle preference for native and exoticHypericumspecies and whether beetle herbivory influences the spatial distribution ofH. punctatum. We found that the introduced beetle readily consumes nativeH. punctatumin addition to its intended target, and thatH. punctatumat our field sites generally occurs along forest edges despite higher performance of experimental plants in more open habitats. However, we found no evidence that the beetle limitsH. punctatumto forest edge habitats.