Biological and Environmental Impact of Adventive Plant-Feeding Herbivores on Native and Non-Native Thistles

EPA Grant Number: F5F71436
Title: Biological and Environmental Impact of Adventive Plant-Feeding Herbivores on Native and Non-Native Thistles
Investigators: Wiggins, Gregory J.
Institution: University of Tennessee - Knoxville
EPA Project Officer: Zambrana, Jose
Project Period: August 1, 2005 through July 1, 2007
Project Amount: $63,228
RFA: GRO Fellowships for Graduate Environmental Study (2005) RFA Text |  Recipients Lists
Research Category: Academic Fellowships


Non-target impacts of introduced biological control agents on native plants are becoming an increasing ecological concern. This research will examine the effects of two adventive weevil species, Trichosirocalus horridus (Panzer) and Rhinocyllus conicus Froelich, which were released as biological control agents against the exotic invasive species musk thistle, Carduus nutans (L.), on non-target native and non-native thistles in Tennessee. One of these weevils, R. conicus, recently has been implicated in the infestation of native thistle species, including rare species, in the midwestern and western U.S. This research will address the environmental impacts of these two weevil species on musk thistle, as well as on other non-target thistle species, especially native thistles that have not been studied elsewhere.

The objectives of this research are to:

  1. determine life histories of all native Cirsium and exotic Cirsium and Carduus thistles in Tennessee and assess their phenological synchrony with the introduced herbivorous insect species,
  2. quantify incidence and impact of introduced plant-feeding weevils on infested thistle species,
  3. identify site conditions suitable for thistle occurrence,
  4. and utilize global information systems (GIS) with spatial analysis to identify potential suitable sites for thistle growth and weevil impact.


Populations of the five native Cirsium species and the three exotic thistles species that occur within Tennessee will be identified and surveyed throughout the state. Plants from each population will be collected and examined for impact by both species of weevil. Plant and site characteristics will be measured and recorded, and spatial analysis incorporating phenological synchrony of the plants and insects will be used to generate GIS models to predict areas of thistle occurrence and thistle/weevil interaction.

Expected Results:

This research will determine if these weevils are feeding on native Cirsium thistles found in Tennessee, and, if so, what impact they have on populations of native species. The use of GIS models will facilitate the accomplishment of this study by identifying potentially critical site characteristics necessary for a given species, or identifying where exotic and native species populations may most likely interact. Once developed, the protocols for generating these models may be modified for regions where non-target impacts on rare, threatened, or endangered species may be of concern.

Supplemental Keywords:

fellowship, Rhinocyllus conicus, Trichosirocalus horridus, Cirsium, Carduus, musk thistle, native thistle, non-target, biological control, GIS, spatial analysis, phenological synchrony, invasive species, population impact,, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Environmental Monitoring, Ecology and Ecosystems, habitat dynamics, biodoversity, biological control agent, invasive plant species, weevil species, ecological consequences, thistles

Progress and Final Reports:

  • 2006
  • Final