Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Proceedings
Publication Acceptance Date: January 14, 2014
Publication Date: N/A
Technical Abstract: Pale and black swallow-wort (Vincetoxicum rossicum and V. nigrum; Apocynaceae, subfamily Asclepiadoideae) are European viny milkweeds that have become invasive in many habitats in the northeastern U.S.A. and southeastern Canada. A defoliating moth from the Ukraine, Hypena opulenta (Christoph) (Lepidoptera: Erebidae) has been released in Canada and may soon be released in the United States for the biological control of swallow-wort. The moth was originally collected in a forested habitat. Its potential multivoltinism, and hence repeated defoliation of swallow-wort, may be promising for controlling swallow-worts, especially when combined with low light conditions of an understory environment. We conducted a greenhouse study of the impact of larval defoliation on seedlings and adult plants of pale and black swallow-wort at different frequencies (once or twice) and degrees of defoliation (50 or 100 percent-seedlings, 3 or 6 larvae/stem-adult plants). Defoliation took place under two forest light regimes: low light conditions typical of deep-shade forest habitats (around 2% of full sun) and higher light levels representative of a more open canopy or forest edge (around 9% of full sun). As expected, plants grown under higher light conditions were generally larger (stem length, stem and root biomass) and produced much more seed than heavily-shaded plants. Plant response to damage interacted with light conditions and swallow-wort species. For example, only seedlings of black swallow-wort that were grown under low light and had been completely defoliated twice had high mortality. In general, severe defoliation (100 percent) and/or high defoliation frequency (twice) were needed to reduce plant biomass and decrease seed production by greater than 70 percent, especially under higher light conditions. Pale and black swallow-wort seedlings and adult plants appear to be fairly tolerant of moderate defoliation damage under the different light conditions they may experience in forests. High levels of repeated defoliation may be needed for suppression of forest infestations of swallow-wort.