The developing larvae of the gall flies effectively decrease seed production of the knapweed. The gall flies lay their eggs in the undeveloped flower heads of knapweed. quadrifasciata) were introduced in the early 1970s to control populations of spotted knapweed. The figures used in this jigsaw activity come from peer-reviewed articles which report information on the indirect effects of two Urophora species (gall flies) which were introduced to control populations of the invasive spotted knapweed ( Centaurea maculosa). Less frequently reported are the indirect effects that introduced agents can have on food web interactions. Typically, such reported negative effects have included instances of host-switching or non-target effects. ![]() ![]() ![]() Further, introduced biocontrol agents have been found to have unanticipated and negative effects on the community to which they are introduced. :: BACKGROUND :: :: FIGURES :: :: STUDENT INSTRUCTIONS :: :: NOTES TO FACULTY :: BACKGROUNDÄ«iological control is a costly means to control invasive species and also a risky endeavor, as not all biological control agents introduced manage to effectively control target species.
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