Flies to control weeds lead to more mice-carried virus: Biocontrol gone wrong, chapter II
Posted by David Brooks | Friday, May 18, 2012
My previous post mentioned an example of a nice-sounding biocontrol of invasive species and how it can fail, which I learned from this week's Science Cafe. Here's another tale that is particularly interesting because the unintended consequence is so off-the-wall. It was told to us by post-doctoral fellow Jeff Evans of Dartmouth.
A gall fly that eats the seeds of a nasty invasive called spotted knapweed was released in Montana in the 1970s. It sounded like a perfect biocontrol, and it sort of worked. The flies multiplied and laid their larvae in the flowers, and the larvae spent the winter eating the seeds.
Alas, they didn't enough seeds to make a difference in the population of knapweed, which like many weeds produces millions and millions of excess seeds - so many that not even insects can keep up. All that happened is that the scads of knapweed flowers now contained some tasty protein tidbits. And who liked that protein? Mice seeking winter food.
As a result, the population of deer mice soared. This is bad because out west they can carry hantavirus, a nasty virus they carry which can be transmitted to humans with sometimes fatal results. Cases of hantavirus in humans has also soared. (Hereabouts, deer mice a the biggest vector of Lyme disease, so anything that helps them is bad for us.)
In other words, using a fly to control an invasive weed not only failed to control the weed but has resulted in more human disease from a virus that's carried by mice. Who would have predicted that?
Nobody, of course, which is why biocontrols which sound so wonderful to us laymen should be approached with caution.