Testing biological control agent compatibility

Cyphocleonus achates and Larinus minutus on diffuse knapweed

Andrea E A Stephens*, Judith H. Myers

*Corresponding author for this work

Research output: Contribution to journalArticle

3 Citations (Scopus)


While weed biological control success is typically achieved with one agent, multiple agents are invariably introduced. Biological control agents that share a host-plant may interact either directly or indirectly through changes in host-plant quality. Negative interactions could reduce the impacts of the agents on the density of their host-plant while positive interactions (facilitation) could improve biological control success.In the Okanagan Valley of British Columbia, Canada, initial declines in the invasive rangeland weed, diffuse knapweed (Centaurea diffusa) were attributed to the introduction of the weevil Larinus minutus. A second weevil, Cyphocleonus achates has recently become common on diffuse knapweed. We sought to determine if the recent increase of C. achates could threaten the success of L. minutus. We considered whether L. minutus colonisation or performance remained the same when C. achates was present, and whether the two agents acted independently to reduce plant performance.Neither changes in colonisation rates nor competitive interactions were apparent between C. achates and L. minutus. Both insects reduced plant performance and, for all metrics, the reduction in plant performance by one species was independent of the second. The two agents appear to be compatible and both should contribute to the control of diffuse knapweed. To assess how biological control agents interact requires understanding both their competitive interactions and their joint effects on the shared host.

Original languageEnglish
Pages (from-to)48-53
Number of pages6
JournalBiological Control
Publication statusPublished - Mar 2014


  • Centaurea diffusa
  • Cyphocleonus achates
  • Diffuse knapweed
  • Indirect interactions
  • Insect competition
  • Larinus minutus
  • Plant-mediated interactions

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