The main cause of the monarch butterfly’s decline is the loss of milkweed — its food — in its U.S. breeding grounds, a new study in the Journal of Animal Ecology has found. That all but confirms that the spread of genetically modified crops is indirectly killing the monarch.
The leaves of the milkweed plant are the only place that monarchs lay their eggs and the only food that monarch butterfly caterpillars will eat. A large proportion of monarchs east of the Rocky Mountains breed in the U.S. corn belt, stretching from Kansas in the west to Ohio in the east, and south to north from Missouri to North Dakota.
The new study led by Tyler Flockhart, currently a postdoctoral researcher at the University of Guelph, showed that the number of milkweed plants in the U.S. corn belt, where most monarchs breed, has fallen 20 per cent over the past few decades. “It’s a massive number of milkweeds — about 1.5 billion milkweed plants,” he said.
Study co-author Ryan Norris, a biology professor at the University of Guelph, said that “likely the biggest cause of loss of milkweed is the adoption of genetically modified crops.” Farmers have been increasingly planting corn and soybeans resistant to herbicides, and then applying those herbicides liberally on their fields. That kills off plants between the rows of crops that aren’t resistant, such as milkweed.
Flockhart said the study shows that a huge quantity of milkweed would need to be replanted in order for monarch butterfly populations to recover. He suggests taking advantage of roadsides for this purpose, and mowing the milkweed at strategic times to maximize their use by monarch butterflies, which prefer younger plants.
Read the full, original article: Monarch butterfly decline linked to spread of GM crops