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Monarch Breeding Map

Click on the map to download or view the PDF version

As these maps show, the American Midwest is ground zero for both GE crops and Monarch breeding. Until recently, common milkweed in the Midwest - where roughly half of these Monarchs are born—has grown primarily in and around corn and soybean fields. [i] This massive use of glyphosate with Roundup Ready crops has decimated milkweeds in Midwestern corn and soybean fields. Researchers estimate that the number of milkweeds in Iowa corn and soybean fields has decreased by 98.7% between 1999 and 2012. [ii]


[i] Hartzler RG (2010) Reduction in common milkweed (Asclepias syriaca) occurrence in Iowa cropland from 1999 to 2009. Crop Protection 29, 1542–1544. [ii] Pleasants (in press), Monarch Butterflies and Agriculture, Ch. 14 in: "Monarchs in a Changing World: Biology and Conservation of an Iconic Insect" Cornell Univ. Press