A 2012 study by John Pleasants and Karen Oberhauser published in Insect Conservation & Diversity has found a correlation between the monarch butterfly population decline and the loss of their breeding habitat, the common milkweed. Since the late 1990s, there has been an increased use of genetically modified, glyphosate-resistant soy and corn. These crops are more tolerant to the herbicide glyphosate, which inhibits the growth proteins in plants, causing weeds to die quickly. Milkweed is an important habitat for monarch breeding, and an unintended target of this herbicide.
The increased planting of these crops has led to increased use of glyphosate – up from 1.4 million kg to 41.7 million kg from 1994 to 2006 in soybeans and from 1.8 million kg to 28.5 million kg in corn from 2000 to 2010. Milkweed is susceptible to this herbicide, which is evident in the 58% decline in the croplands of the Midwest. Monarchs overwinter in Mexico, but make the annual 2,500 mile journey to the Midwest in search of milkweed so they can reproduce.
Milkweed is a vital food source and habitat for eggs and caterpillars, and glyphosate use is a huge threat to the survival of monarch butterflies. The Midwest has already seen an 81% decline in monarch reproduction, and if we do not take action, we may lose this endangered biological phenomenon altogether.
You can take action to conserve the monarch butterfly by: