There is a direct parallel between the demise of milkweeds — killed by the herbicide glyphosate, which is sprayed by the millions of gallons on fields where genetically modified crops are growing — and the steady drop in monarch numbers.
To anyone who has grown up in the Midwest, the result seems very strange. After decades of trying to eradicate milkweed, gardeners are being encouraged to plant it in their gardens, and townships and counties are being asked to let it thrive in the roadside ditches. What looks like agricultural success, purging bean and corn fields of milkweed (among other weeds), turns out to be butterfly disaster. This is the great puzzle of species conservation — it has to be effective at nearly every stage of a species’ life cycle. And this, too, is the dilemma of human behavior. We live in a world of unintended consequences of our own making, which can never be easily undone.
By Verlyn Klinkenborg. Taken from:http://www.nytimes.com/2013/10/13/opinion/sunday/monarchs-fight-for-their-lives.html?smid=tw-share&_r=1&