A nice article in this morning’s New York Times, “A Weed, a Fly, a Mouse, and a Chain of Unintended Consequences,” gives another lesson of one of the hazards of using biological control — unanticipated ecological chain reactions.
The most common thing to go wrong when introducing one non-native organism to combat another is host-switching; I wrote about one example, parasitic flies introduced to control gypsy moths, which ended up attacking giant silk moths. The Times article gives other instances.
However, the article focuses on the introduction of a gall fly in the western U.S. to control Spotted Knapweed (Centaurea biebersteinii), a European weed species that is highly invasive. The fly (Urophora sp.) lays its eggs in the flower head and the larvae feed on the seeds.
The crystal ball failed to foresee that mice would find these larvae excellent winter food. All those larvae were readily available to mice in the knapweed seed heads, which stick up through the snow. Mice populations have soared, and these mice can carry hantavirus.
The article goes on to outline the debate over using biocontrol agents, but I expect this story doesn’t really end with the concern over hantavirus. Mice have pretty profound impacts on energy flows in ecosystems as seed dispersers or consumers, predators and prey. I don’t think we’ve heard the last about how this change in mouse population dynamics impacts the environment.
- Ortega, Y. K., D. E. Pearson, and K. S. McKelvey. 2004. Effects of biological control agents and exotic plant invasion on deer mouse populations. Ecological Applications 14:241-253.
- Pearson, D.E., K.S. McKelvey, and L. F. Ruggiero. 2000. Non-target effects of an introduced biological control agent on deer mouse ecology. Oecologia 122: 121–128.
Photo: Michael Shephard, USDA Forest Service.
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Very nice write-up!
Here's some more primary lit links for y'all, from the authors of the study:
Biological control agents elevate hantavirus by subsidizing deer mouse populations (Ecology Letters v. 9, 2006) – darn it, Blackwell's site is down right now but I used this link Saturday!
Indirect effects of host-specific biological control agents (TREE v. 118, 2003)
Now they need more raptors to control the mice.