A retrospective analysis of known and potential risks associated with exotic toadflax-feeding insects

To date, eight exotic toadflax-feeding insect species have been accidentally or intentionally introduced to North America. Reports on their establishment and impact have been recorded for more than 60 years. Environmental risks linked to biological control of toadflax were identified in terms of host resources and undesirable impacts on the target species through the critical review of this record. Data gaps revealed during this retrospective analysis are addressed through suggestions for future research and associated experimental methodologies. Known and potential impacts of toadflax-feeding insects on both invasive toadflax and non-target species are examined. Recent programmatic demands for demonstrated agent efficacy and stringent host selectivity during the prerelease screening process clearly illustrate that classical biological control of invasive toadflax in North America is progressing beyond the so-called lottery approach.