Identifying critical life stage transitions for biological control of long-lived perennial Vincetoxicum species

Authors: Milbrath, Lindsey; Davis, Adam; Biazzo, Jeromy

Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2017
Publication Date: 1/9/2018
Citation: Milbrath, L.R., Davis, A.S., Biazzo, J. 2018. Identifying critical life stage transitions for biological control of long-lived perennial Vincetoxicum species. Journal of Applied Ecology. 55:1465-1475. https://doi.org/10.1111/1365-2664.13065.
DOI: https://doi.org/10.1111/1365-2664.13065

Interpretive Summary: Modelling of weed populations can help identify both key points in their life cycle to target and determine how much damage is needed to successfully control them. In turn, this information can guide the pre-release selection of effective biological control agents. Pale and black swallow-wort are exotic, invasive weeds of natural areas and managed lands in northeastern North America. We collected data from six field and forest populations of the two species, and determined that combinations of reduced survival, growth, or seed production were generally needed to provide control. The levels of damage caused by leaf-feeding moths or seed-destroying flies is promising for controlling slow-growing populations of the weeds (forest and some field), and they are recommended for release as biological control agents. However, fast-growing field populations will not be controlled with these insects, and other control measures will need to be integrated for successful management of these weeds.

Technical Abstract: Demographic matrix modeling of invasive plant populations can be a powerful tool to identify key life stage transitions for targeted disruption in order to cause population decline. This approach can provide quantitative estimates of reductions in select vital rates needed to reduce population growth rates below replacement levels and can inform the pre-release selection of effective biological control agents, as in the case of two invasive Vincetoxicum species in North America. We parameterized a five life-stage matrix model using vital rate data from six populations (field and forest) of V. nigrum and V. rossicum. Elasticity analyses were used to identify life stage transitions and associated vital rates for perturbation through the incorporation of per capita impact data of candidate biological control agents. Several survival, growth and fecundity-related transitions were identified that were mostly similar across species, habitats and locations, although two populations showed unique population dynamics. Reductions in associated vital rates needed to prevent population growth varied greatly among populations. Defoliation damage and predispersal seed predation, both of which reduced fecundity, can be effective against slower-growing forest and field populations of Vincetoxicum species. A fly and bivoltine moth are recommended as priority agents. However, biological control with these same agents will be ineffective against other field populations as well as some forest populations if the intensity of damage is not severe. Control of long-lived perennial plants, such as species of Vincetoxicum, is projected to occur through disruption of some individual vital rates of survival, growth or fecundity if population increase is relatively low (population growth rates < 1.6). However, without significant and simultaneous reductions in multiple lower-level vital rates, faster-growing populations will not be controlled with biological control or other management tools.