GMOs not main culprit in monarch butterfly decline
Using digitized records from museums and herbaria throughout North America, the researchers were able to track the relative abundance of both monarchs and milkweeds for more than a century, from 1900 to 2016. They found that both monarchs and milkweeds increased during the early 20th century and recent declines are actually part of a much longer trend beginning around 1950.
"Herbicide resistant crops are clearly not the only culprit, and likely not even the primary culprit," the paper states. "Not only did monarch and milkweed declines begin decades before GM crops were introduced, but other variables, particularly a decline in the number of farms, predict common milkweed trends more strongly over the period studied."
Read the full study "Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops" at phys.org.