Monarch butterfly decline linked to spread of GM crops

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 has found. That all but confirms that the spread of genetically modified crops is indirectly killing the monarch.

This past winter, the number of monarch butterflies wintering in Mexico fell to its lowest since 1993, when records first started being kept, the World Wildlife Fund and Mexico's Environment Department reported in January. That report blamed the loss of milkweed owing to genetically modified crops and urban sprawl in the U.S. and illegal logging in the butterflies' Mexican wintering ground.

Monarch migration said to be in trouble as numbers fall
Now, an analysis combining all the known data about monarch populations and the factors that influence them shows that the monarch's biggest threat is in the U.S., not Mexico.

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.

http://www.cbc.ca/news/technology/monarch-butterfly-decline-linked-to-spread-of-gm-crops-1.2665131