The Decline of Monarch Butterflies

There was a piece on CBS Sunday Morning about the decline in numbers of Monarch butterflies.  In it they mentioned that populations were thought to be declining due to pesticides which eliminated their main food source, milkweed.  It doesn't take a rocket scientist to put together that this is mainly due to Roundup Ready corn and soybeans.  Here's the New York Times in 2011:

Monarchs lay their eggs on milkweed, and their larvae eat it. While the evidence is still preliminary and disputed, experts like Chip Taylor say the growing use of genetically modified crops is threatening the orange-and-black butterfly by depriving it of habitat.
“This milkweed has disappeared from at least 100 million acres of these row crops,” said Dr. Taylor, an insect ecologist at the University of Kansas and director of the research and conservation program Monarch Watch. “Your milkweed is virtually gone.”
The primary evidence that monarch populations are in decline comes from a new study showing a drop over the last 17 years of the area occupied by monarchs in central Mexico, where many of them spend the winter. The amount of land occupied by the monarchs is thought to be a proxy for their population size.
“This is the first time we have the data that we can analyze statistically that shows there’s a downward trend,” said Ernest H. Williams, a professor of biology at Hamilton College and an author of the study along with Dr. Taylor and others.
The paper, published online by the journal Insect Conservation and Diversity, attributes the decrease partly to the loss of milkweed from use of “Roundup Ready” crops. Other causes, it says, are the loss of milkweed to land development, illegal logging at the wintering sites in Mexico, and severe weather.

Of course, they include some people who deny any link (I bet they have research funded by Monsanto).  But from personal experience, I don't remember the last time I saw milkweed in the field.  As a kid, it was everywhere.  Then again, I haven't seen too many Monarch butterflies recently.  While that may not be the worst thing in the world, it is a somewhat scary indicator of what unforeseen  changes we wreak on the environment around us.