Trophic Interactions and Biological Control

EPA Grant Number: U916004
Title: Trophic Interactions and Biological Control
Investigators: Stanley, Amanda G.
Institution: University of Washington
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $92,204
RFA: STAR Graduate Fellowships (2001) RFA Text |  Recipients Lists
Research Category: Fellowship - Terrestrial Ecology and Ecosystems , Academic Fellowships , Ecological Indicators/Assessment/Restoration


Biological control has the potential to be a cost-effective alternative to pesticides; however, the current success rate for biocontrol of invasive plants is very low. Improving the efficacy of biological control requires an understanding of what causes success or failure. Many biocontrol agents successfully establish and spread, but fail to suppress the target weed. The objectives of this research project are to determine whether: (1) the control attacks a robust life stage of the target, such that damage to individual plants does not produce a population-level effect; and (2) interactions with other native species (e.g., predation or competition) suppress the biocontrol populations below some threshold needed for control.


To address these hypotheses, I explore interactions between spotted knapweed (Centaurea maculosa), two seedhead gallfly biocontrol agents (genus Urophora), and a native generalist predator, the deer mouse Peromyscus maniculatus. The two gallfly species were successfully established about 30 years ago and are now very abundant, but have caused no reduction in knapweed density or rate of spread. The mice consume vast quantities of gallfly larvae during the winter; one mouse can eat more than 1,000 larvae/night. Enclosure/exclosure experiments show that this intense overwinter predation of gallflies by deer mice is suppressing gallfly densities. Even at high densities, however, gallflies have little effect on knapweed recruitment. Although gallflies can significantly reduce seed production of C. maculosa, recruitment of this weed does not appear to be seed limited. Therefore, preliminary results suggest that gallflies failed because they attack a robust life stage of their target weed. Therefore, other seed-feeding insects are unlikely to be effective biocontrol agents for Centaureaspecies.

Supplemental Keywords:

fellowship, trophic interactions, biological control, pesticides, invasive plants, Centaurea maculosa, Peromyscus maniculatus, seed-feeding insects, biocontrol.

Progress and Final Reports:

  • 2001
  • 2002
  • Final