Musk thistle, Carduus nutans L., is an invasive exotic plant introduced into the U.S. more than 100 years ago. Often growing in extremely dense patches, musk thistle can locally out-compete virtually all native vegetation and can detrimentally affect farm lands by limiting the amount of pasture land available for grazing. Musk thistle can also be a problem along roadways by obstructing road signs and interfering with roadside beautification programs. Compounding the problem, many areas infested with musk thistle are either inaccessible to mowers or impractical to spray with herbicides. Two weevil species, Trichosirocalus horridus (Panzer) and Rhinocyllus conicus Froelich, are known to feed on musk thistle in Europe where it is rarely considered a problem plant. Both weevil species have been widely released throughout the U.S. In 1989, a project utilizing T. horridus and R. conicus as biological control agents of musk thistle was initiated in Tennessee. Although initial releases were made in a few counties in 1989, weevils had been released in about 15 counties in eastern Tennessee by 1992. In May and June 2001, stands of musk thistle were evaluated at three sites in each of 13 counties in eastern Tennessee. At each site, 10 plants were randomly selected, and the number of weevil adults, weevil eggs, plant height, stage of development, number of lateral stems, length of lateral stems, etc. were recorded. Plant buds/flowers/seed heads were clipped and taken to the laboratory, where they were bioassayed for weevil larvae and/or pupae. At each site, plant density and stand size were measured. Data on weevil numbers and impact of weevils on seed production of musk thistle will be presented.
Species 1: Coleoptera Curculionidae Trichosirocalus horridus
Species 2: Coleoptera Curculionidae Rhinocyllus conicus
Keywords: Exotic vegetation, Biological control
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA