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

Abstract

Demographic matrix modelling of invasive plant populations can be a powerful tool to identify 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 rate (λ) below 1 and can inform the prerelease 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 Vincetoxicum nigrum and Vincetoxicum 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 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 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. Synthesis and applications. 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 low to moderate (λ < 1.6). However, without significant and simultaneous reductions in multiple lower level vital rates, faster growing populations will not be contained with biological control or other management tools.

An experimental application of Hypena opulenta as a biocontrol agent for the invasive vine Vincetoxicum rossicum

“…rossicum, understanding its distribution and ecology (Averill, DiTommaso, Mohler, & Milbrath, 2011;DiTommaso, Lawlor, & Darbyshire, 2005;Milbrath, Davis, & Biazzo, 2017;Miller & Kricsfalusy, 2007), the mechanisms driving its invasion (Bongard, Butler, & Fulthorpe, 2013;Cappuccino, 2004), its impact on ecosystems (Ernst & Cappuccino, 2005;Bugiel, Livingstone, Isaac, Fulthorpe, & Martin, 2018;Livingstone et al, in press) and the effectiveness of physical and chemical control (Averill et al, 2011) have all been important research priorities. V. rossicum is a perennial vine.…”

Response of pale swallowwort (Vincetoxicum rossicum) to multiple years of mowing

“…A biological control program is being implemented with the first release of an agent in 2013 (Young and Weed 2014). However, the agent Hypena opulenta (Christoph) (Lepidoptera: Erebidae) may not attack Vincetoxicum plants in open fields, or if it does, its projected impact in such habitats may be minimal (Milbrath et al 2018). Mechanical control is generally only considered to be suitable for small patches or for reducing seed production (Averill et al 2008;Christensen 1998;DiTommaso et al 2013).…”

“…Mechanical control is generally only considered to be suitable for small patches or for reducing seed production (Averill et al 2008;Christensen 1998;DiTommaso et al 2013). Despite mowing having broad impacts on other associated plant species, mowing is still a common practice for fields infested with V. rossicum, especially as open field infestations usually achieve the highest densities, have the highest population growth rates, and produce the greatest amounts of seeds for dispersing to new areas (Averill et al 2011;Milbrath et al 2018;Smith et al 2006).…”

Preference and performance of Hypena opulenta on Vincetoxicum rossicum foliage from sun versus shade habitats

“…The vine produces wind-dispersed, poly-embryonic seeds, with erect stems that range from 40 to 200 cm in length . V. rossicum expands its range by seed, released by ripened pods in late summer, but can also expand locally by stem production from root crowns Milbrath et al 2018 There are few herbivores in North America that will feed on V. rossicum. Monoculture stands of V. rossicum have significantly lower arthropod abundance and diversity than native old field plants (Ernst & Cappuccino 2005).…”

“…year . Hypena opulenta was approved for release as a biological control agent for swallow-worts in Canada in 2013 and approved for release in the United States in 2017 (Milbrath et al 2018).…”