Indirectly, it seems:
The vast majority of monarchs that arrive in Mexico grew up eating milkweed in the United States and Canada, according to Karen Oberhauser, professor at the University of Minnesota who has studied the monarch for more than 30 years, and is a leading scientist on this butterfly. "Numerous lines of evidence demonstrate that the Corn Belt in the US Midwest is the primary source for monarchs hibernating in Mexico," said Oberhauser. Large part of the monarchs' reproductive habitat in this region has been lost to changing agricultural practices, namely an explosion in the use of crops that allow post-emergence treatment with herbicides. "These genetically modified crops have resulted in the extermination of milkweed from many agricultural habitats," added Oberhauser.
Every August, the local monarch population puts on a show as it prepares to head south to Mexico. Here's what T.O. residents will miss should we lose them.