Projected impacts of swallow-wort biological control agents

Pale and black swallow-wort (Vincetoxicum rossicum and V. nigrum; Apocynaceae) are perennial vines from Europe that are invasive in various terrestrial habitats in the northeastern USA and southeastern Canada. Biological control agents of swallow-worts should be both host-specific as well as effective in suppressing swallow-wort populations. Demographic matrix modelling of invasive plant populations can be a powerful tool to identify life stage transitions for targeted disruption, and thus inform pre-release recommendations of particularly effective biological control agents. A five life-stage matrix model, using data from six field or forest populations of both swallow-wort species and incorporating per capita impact data of select candidate agents, was used to project agent impacts. Season-long defoliation damage or predispersal seed predation may suppress slow-growing, but not fast-growing, forest and field populations of swallow-worts. Other agents that damage swallow-worts in different ways may also be effective but impact data for them is incomplete. Faster-growing field populations of swallow-wort likely require complete seed destruction annually, a combination of compatible agents, and/or a combination of tactics in order to control them.