Biological Invasions

, 13:2233 | Cite as

Priority resource access mediates competitive intensity between an invasive weevil and native floral herbivores

  • S. M. Louda
  • T. A. Rand
  • A. A. R. Kula
  • A. E. Arnett
  • N. M. West
  • B. Tenhumberg
Original Paper


Mechanisms underlying invasive species impacts remain incompletely understood. We tested the hypothesis that priority resource access by an invasive biocontrol weevil, Rhinocyllus conicus, intensifies and alters the outcome of competition with native floral herbivores over flower head resources of the non-target, native host plant Cirsium canescens, specifically with the predominant, synchronous tephritid fly Paracantha culta. Four main results emerged. First, we documented strong, asymmetric competition, with R. conicus out-competing P. culta. Second, weevil priority access to floral resources accelerated competitive suppression of P. culta. Evidence for competitive suppression with increased weevil priority included decreases in both the numbers and the total biomass of native flies, plus decreases in individual P. culta fly mass and, so, potential fitness. Third, we found evidence for three concurrent mechanisms underlying the competitive suppression of P. culta by R. conicus. Prior use of a flower head by R. conicus interfered with P. culta pre-oviposition behavior. Once oviposition occurred, the weevil also reduced fly post-oviposition performance. Preemptive resource exploitation occurred, shown by the significant effect of flower head size on the total number of insects developing and in the magnitude of R. conicus effects on P. culta. Interference also occurred, shown by a spatial shift of surviving P. culta individuals away from the preferred receptacle resources as R. conicus priority increased. Finally, fourth, using an individual-based model (IBM), we found that the competitive interactions documented have the potential for imposing demographic consequences, causing a reduction in P. culta population sizes. Thus, priority resource access by an invasive insect increased competitive impact on the predominant native insect in the invaded floral guild. This study also provides the first experimental evidence for non-target effects of a weed biological control agent on an associated native insect herbivore.


Floral herbivores Insect competition Insect phenology Invasive species Individual based model Demographic effects Non-target effects of biological control Biocontrol 



We thank Kayla Christensen for energetic help in the field, Chad Andersen and Nate Brandt for conscientious help in the lab, and Steve Archer for discussions on data handling and analyses of the initial experiment. We appreciate the logistical support provided by UNL Cedar Point Biological Station staff and the financial support provided by NSF grant DEB 96-15299 to S. M. L., a D. H. Smith Conservation Research Fellowship to T. A. R., and a Howard Hughes Medical Institute Scholarship for the Summer Independent Research Experience to A. A. R. K. We appreciate the stimulus for improvement provided by the comments of an anonymous reviewer, and the insightful suggestions of the Editor-in-Chief, Dan Simberloff. USDA is an equal opportunity provider and employer.

Supplementary material

10530_2011_36_MOESM1_ESM.doc (416 kb)
Supplementary material 1 (DOC 416 kb)
10530_2011_36_MOESM2_ESM.doc (44 kb)
Supplementary material 2 (DOC 44 kb)


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Copyright information

© Springer Science+Business Media B.V.(outside the USA) 2011

Authors and Affiliations

  • S. M. Louda
    • 1
  • T. A. Rand
    • 1
    • 3
  • A. A. R. Kula
    • 1
    • 4
  • A. E. Arnett
    • 1
    • 5
  • N. M. West
    • 1
  • B. Tenhumberg
    • 1
    • 2
  1. 1.School of Biological SciencesUniversity of NebraskaLincolnUSA
  2. 2.Department of MathematicsUniversity of NebraskaLincolnUSA
  3. 3.USDA, Agricultural Research ServiceNorthern Plains Agricultural Research LaboratorySidneyUSA
  4. 4.Program in Behavior, Ecology, Evolution and SystematicsUniversity of MarylandCollege ParkUSA
  5. 5.Center for BiodiversityUnity CollegeUnityUSA

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