If you can deal with the ick factor of mice in their millions, you may find the following interesting (links at bottom). After the ten year drought in Australia there was a bumper harvest. That encouraged an explosion of mice. Their natural predators are theorised to have decreased in number during the drought years. Apparently the only solution is poison.
I watched part of a tv program (Landline) on the issue yesterday. It was interesting that one farmer found the mice riddled the paddock which last year had the bumper barley crop. But the paddock next door, the one that had held livestock, was green and unriddled by mice. But after so many years of drought and struggle, could anyone give up the chance of a bumper crop because the next year would hold mice?
ABC article, the company that produces the mouse poison, Adelaide Now, and you can find video coverage here--although I haven't watched it so not sure of the ick factor.
And then there are the locusts...