Impact of Abrostola asclepiadis combined with other stressors on invasive swallow-worts (Vincetoxicum species)

Authors: Milbrath, Lindsey; Biazzo, Jeromy; DITOMMASO, ANTONIO - Cornell University; MORRIS, SCOTT - Cornell University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2018
Publication Date: 1/24/2019
Citation: Milbrath, L.R., Biazzo, J., Ditommaso, A., Morris, S.H. 2019. Impact of Abrostola asclepiadis combined with other stressors on invasive swallow-worts (Vincetoxicum species). Biological Control. 130:118-126. https://doi.org/10.1016/j.biocontrol.2018.11.005.
DOI: https://doi.org/10.1016/j.biocontrol.2018.11.005

Interpretive Summary: A moth is being studied as a potential biological control agent for pale and black swallow-wort, invasive vines from Europe that were introduced into North America. Other plant stresses are known to increase the effect of insect damage when they are combined. We studied the moth’s impact by itself on the weeds and in combination with shading or competition with a grass. Although one round of defoliation could decrease aboveground biomass and seed production, large reductions only occurred if plants were completely defoliated two times. However, the moth will likely only defoliate swallow-wort once every year. Shading and grass competition also reduced plant growth but did not enhance insect damage to swallow-worts. Our results suggest that the moth will have a limited effect on the weeds, and it should not be released at this time.

Technical Abstract: The moth Abrostola asclepiadis (Lepidoptera: Noctuidae) is being investigated for the biological control of two swallow-wort species (Vincetoxicum, Apocynaceae), European vines introduced into North America. Limited information existed on its potential impact on swallow-worts, and the combination of defoliation damage by A. asclepiadis and other stresses to the plants had not been studied. We conducted greenhouse studies of the impact of different frequencies (once or twice) and degrees of defoliation (50 or 100%-seedlings; one or two larvae per stem-mature plants) by larvae on seedlings and mature (flowering) plants of black and pale swallow-wort. Defoliation was combined with varying light levels (shaded or not) or competition with quackgrass (Elymus repens). Significant reductions in aboveground dry mass and seeds generally only occurred when plants were completely defoliated twice. Grass competition and, to a greater extent, shading reduced growth and reproduction of swallow-wort plants. However, very few interactions between defoliation and the other stressors occurred, suggesting they would have an additive effect. Because A. asclepiadis will likely be univoltine if it were to be released in North America, its impact appears to be limited even if severe defoliation could be achieved. Therefore, A. asclepiadis should be given a lower priority for release.