Impact of herbivory on performance of Vincetoxicum spp., invasive weeds in North America

Abstract

The alien invasive vines Vincetoxicum rossicum and Vincetoxicum nigrum (swallow-wort) are of major concern in eastern North America, where both species invade forested landscapes and threaten faunal and plant diversity. Among the few native natural enemies reported in Eurasia, the specialist chrysomelid, Chrysochus (Eumolpus) asclepiadeus (Coleoptera; Chrysomelidae), feeds on Vincetoxicum both above ground (as adults) and below ground (as larvae). The goal of our study was to assess the potential for using this beetle to manage invasive Vincetoxicum spp. in North America by quantifying the impact of herbivory by C. asclepiadeus on Vincetoxicum and determining whether this effect was influenced by plant density (''Allee effect''). Experimental work was carried out using a split plot design in the field in southern France. Pots of V. nigrum and V. hirundinaria, a substitute for V. rossicum, were planted at high (255 plants/m 2 ), medium (127 plants/m 2 ), and low (32 plants/m 2 ) plant densities, and received treatments of 0 (control), 2 or 4 C. asclepiadeus adult beetles/pot. Leaf damage, root and shoot biomass, and quantity of seeds were measured after 4 weeks of adult feeding. Densities of 2 and 4 beetles/pot caused similar damage, with significant reductions in plant biomass at low plant density. While V. hirundinaria increased allocation of resources to roots in response to herbivory, V. nigrum did not. Seed production was greatest for both species grown at low plant densities, but only V. nigrum produced fewer seeds in response to herbivory. Our results, based on the effects of herbivory by C. asclepiadeus adults, suggest that if this beetle were to be introduced into North America for the management of Vincetoxicum spp. such as V. rossicum, reductions in plant biomass and spread would be greatest if beetles were released on edges or in newlyestablished satellite populations at low plant densities. In the case of V. nigrum, beetles could be released irrespective of plant density as reproductive output and seed dispersal would be reduced similarly.

Tolerance of Swallowworts (Vincetoxicumspp.) to Multiple Years of Artificial Defoliation and Clipping

“…However, these plants had small root masses at the start of the experiment. Defoliation of swallowwort by different insects reduced aboveground biomass but did not affect root biomass (Maguire et al 2011;Weed and Casagrande 2010;L.R.M. and J.B., unpublished data).…”

“…Currently, only one agent, the defoliating moth Hypena opulenta (Christoph) (Lepidoptera: Erebidae), has been released (in Canada) for swallowwort biological control (Young and Weed 2014). Previous simulated and real herbivory studies with swallowwort indicated minor to large effects on plant growth and reproduction (Doubleday and Cappuccino 2011; Maguire et al 2011;Milbrath 2008;Casagrande 2010, Weed et al 2011a). Artificial or simulated herbivory studies are generally considered representative of real herbivory when measuring plant performance (Hjältén 2004;Lehtilä and Boalt 2004;Raghu and Dhileepan 2005).…”

“…Several candidate insect and pathogen agents have been assessed to varying degrees (Berner et al 2011;Dolgovskaya et al 2014;Gibson et al 2014;Hazlehurst et al 2012;Leroux 2014;Maguire et al 2011;Casagrande 2010, 2011;Weed et al 2011a,b). Given the frequency with which leaf-feeding insects have been used in other programs (Winston et al 2014), it was reasonable to assume that a similar type of agent would be used against swallowworts.…”

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

“…Some candidate agents have been rejected (Dolgovskaya, Volkovitsh, Reznik, Moseyko, & Milbrath, ; Weed & Casagrande, ) or may be rejected pending additional research on host specificity. Thus, their demographic influence on the plants has not been thoroughly investigated (see Maguire, Sforza, & Smith, ; Weed, Gassmann & Casagrande, ). Other candidate agents that appeared to be host specific or had not been screened when demography studies were initiated included the defoliating moths Hypena opulenta (Christoph) (Lepidoptera: Erebidae) and Abrostola asclepiadis (Denis and Schiffermüller) (Lepidoptera: Noctuidae) and the predispersal seed predator Euphranta connexa (Fabricius) (Diptera: Tephritidae; Hazlehurst, Weed, Tewksbury, & Casagrande, ; Weed, Gassmann, Leroux, & Casagrande, ).…”

Pollination, Herbivory, and Habitat Fragmentation: Their Effects on the Reproductive Fitness of Angadenia berteroi, a Native Perennial Plant of the South Florida Pine Rocklands

“…In addition, timing of damage had no significant impact on plant fitness, since pre-flowering and flowering defoliation had similar effects on both growth and reproduction. Negative effects of defoliation on fitness have been reported in other species (Parra-Tabla et al, 2004;Narbona and Dirzo, 2010;Maguire et al, 2011;Irwin and Brody, 2011;Puentes and Ägren, 2012;Zhu et al 2014), where growth and reproduction were reduced as the percentage of defoliation increased.…”