Herbicides aren’t sole culprit in Monarch butterfly decline

Brad Plumer | January 8, 2015

Monarch butterflies are vanishing. Over the last 20 years, fewer and fewer of them have been making the long journey down to Mexico to survive the winter. By one count, their numbers have shrunk as much as 90 percent.

In recent years, some experts have blamed the decline of the monarch butterflies on the rise of new soy and corn crops that are genetically modified to be resistant to herbicides — such as Monsanto’s Roundup. The idea is that this leads to heavier herbicide use, which in turn kills more milkweed.

But not everyone’s convinced that herbicides are the sole reason for the decline of native plants near agricultural fields. Another recent study by scientists at the US Department of Agriculture and Penn State found that herbicide-tolerant native plants around farmland in Pennsylvania were declining at the same rate as less-tolerant plants. That suggests that other factors may be at work here.

The Penn State researchers pointed out that farmers have made a lot of changes in recent decades apart from rising herbicide use — they’ve simplified their crop rotations, segregated crops and livestock, and employed new mechanical farming methods. What’s more, woodlots, hedgerows, pastures, and wetlands have all been cleared to make way for bigger fields. So there may be more going on than just GMOs and herbicides.

Read full, original article: Monarch butterflies could be declared an endangered species. Here’s what that means.