Across much of the monarch 's range , particularly in the midwestern U.S. , milkweed has fallen victim en masse to changing land use and the advent of herbicide-resistant crops . President Obama and his counterparts from Canada and Mexico will be at summit . Carter Roberts , Omar Vidal : They should discuss plight of these butterflies . 2013 was the worst year for these butterflies in recorded history , they said . Roberts , Vidal : They 're a special to North America , we should stop their decline .
President Obama and his counterparts from Canada and Mexico will be at summit . Carter Roberts , Omar Vidal : They should discuss plight of these butterflies . 2013 was the worst year for these butterflies in recorded history , they said . Roberts , Vidal : They 're a special to North America , we should stop their decline .