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Submitted to: Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/11/2016 Publication Date: 2/11/2016 Citation: Milbrath, L.R., Biazzo, J. 2016. Impact of the defoliating moth Hypena opulenta on invasive swallow-worts (Vincetoxicum species) under different light environments. Biological Control. 97:1-12. Interpretive Summary: Pale and black swallow-wort are exotic, invasive weeds of natural areas and managed ecosystems in northeastern North America. A forest moth that defoliates the plants has been requested to be released as part of a biological control program for these weeds. However, limited information exists on its potential impact on the weeds. We evaluated the response of pale and black swallow-wort seedlings and flowering plants to different amounts of defoliation by the larvae under two low light conditions typical of forest infestations in New York State. Increasing degrees of defoliation and/or frequency of defoliation by the moth generally reduced biomass and seed production for both species and life stages, but had no effect on root mass for flowering plants. No flowering plants and few seedlings died. However, all black swallow-wort seedlings died that had been completely defoliated twice under the lowest light levels. Complete defoliation repeated within and across years may be needed for suppression of forest infestations of swallow-wort. Technical Abstract: Black and pale swallow-wort (Vincetoxicum nigrum and V. rossicum, Apocynaceae: Asclepiadoideae) are twining vines from Europe that have become invasive in the northeastern USA and southeastern Canada. Hypena opulenta (Christoph) (Lepidoptera: Erebidae), a defoliating forest moth from the Ukraine, has been released in Canada for the biological control of swallow-wort and a request for release in the United States is under review. Its potential multivoltinism, and hence repeated defoliation of swallow-worts, combined with low-light stress in an understory environment may be promising for controlling forest infestations of swallow-worts. We conducted a greenhouse study of the impact of larval defoliation on seedlings and mature (flowering) plants of black and pale swallow-wort at different frequencies (once or twice) and degrees of defoliation (50 or 100%-seedlings; three or six larvae per stem on mature plants). Defoliation occurred under two forest light-regimes: low-light conditions typical of deeply-shaded forest habitats and higher light levels representative of a more open canopy or forest edge. Increasing degrees of defoliation and/or frequency of defoliation by H. opulenta generally reduced biomass and seed production for both species and life stages, with the exception of root mass for mature plants. No mature plants died and little seedling mortality occurred apart from black swallow-wort that had been completely defoliated twice under low light. Plants grown under higher light conditions were generally larger and produced many more seeds than heavily-shaded plants. Pale and black swallow-wort seedlings and mature plants appear to be fairly tolerant of moderate defoliation damage. Complete defoliation repeated within and across years may be needed for suppression of forest infestations of swallow-wort. |
