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|Title:||Potential for a native weevil to serve as a biological control agent for Eurasian watermilfoil|
|Authors:||Middlebury College. Department of Biology.|
Aquatic Plant Control Research Program (U.S.)
Creed, Robert P.
Sheldon, Sallie P.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: The potential of the North American weevil Euhrychiopsis lecontei to serve as a biological control agent for Eurasian watermilfoil (Myriophyllum spicatum) was evaluated. Attention has focused on E. lecontei because it was found associated with a watermilfoil population in Brownington Pond, Vermont, United States, which had declined from approximately 10 to 11 ha in 1986 to <1 ha in 1989. Watermilfoil abundance was monitored in Brownington Pond from 1990 through 1992. Watermilfoil abundance increased from 1989 through 1991 and decreased again in 1992. Samples of weevils, water, and sediment chemistry suggested that this second decrease in watermilfoil abundance was caused by weevils and not changes in either water or sediment nutrient concentrations. Weevils significantly suppressed lateral stem and root production of watermilfoil in an enclosure experiment conducted in the pond. Damaged stems also lost their buoyancy and settled out of the water column. Weevils were readily cultured in the laboratory. All life stages were produced, and under culture conditions, mean weevil generation time was approximately 1 month. Weevil eggs are laid on meristems; the first instar larvae burrow into and destroy the meristems; older larvae burrow through the stem; and pupation also occurs in the stem. Weevil adults feed and mate on the plants. In a series of pool and aquarium experiments, weevil adults and larvae significantly suppressed watermilfoil growth and reduced stem buoyancy. Adult weevils damaged the plants by feeding on the stem and leaf tissue. Adults removed a considerable number of leaves from the tops of the stems in one experiment. First instar larvae suppressed stem elongation by destroying meristems. Late instar larvae significantly reduced watermilfoil growth in one experiment but not another. Late instar larvae significantly reduced plant growth when watermilfoil exhibited a faster growth rate. The caterpillar Acentria ephemerella also suppressed watermilfoil growth in one of these experiments. In another experiment, stem fragments damaged by weevil larvae produced significantly less stem and root tissue compared with undamaged, control fragments. In similar experiments, weevils did not have a significant effect on the growth of native macrophytes commonly found in Vermont, although they did remove a significant number of leaves from the native, northern watermilfoil (Myriophyllum sibiricum). Weevil survivorship was often considerably lower on some of these native macrophyte species. Collections of three herbivorous insects on watermilfoil were made in the northeastern United States in 1990 and 1991. Euhrychiopsis lecontei was found on watermilfoil in 18 lakes in Vermont, 3 lakes in Connecticut, 4 lakes in Massachusetts, and 1 lake in New York. Acentria was found in 13 lakes in Vermont, 5 lakes in Massachusetts, and 1 lake in New Hampshire. The caterpillar Parapoynx badiusalis was found in five Vermont lakes and in one lake in Connecticut. Collections in Alberta, Canada, suggest that northern watermilfoil is a native host for Euhrychiopsis, as eggs, larvae, pupae, and adults were collected from northern watermilfoil in 10 lakes.
|Appears in Collections:||Technical Report|