Botany Blog Plants of the Northeastern U.S.

March 22, 2012

Monarch Butterfly Populations Declining

The larvae of Monarch Butterflies (Danaus plexippus) feed exclusively on plants in the genus Asclepias (Milkweeds) and a few other related genera.

Monarch caterpillar on butterfly weed

Monarch larva on Butterfly Weed (Asclepias tuberosa)

According to a new study published in the journal Insect Conservation and Diversity (Pleasants & Oberhauser, 2012), overwintering monarch butterfly populations in Mexico have declined by about half since 1999. This is correlated with an estimated 58% decline in milkweed populations in the Midwest and a corresponding decline of 81% in monarch breeding success. These effects are most likely due to the widespread use of Glyphosate on genetically modified crops immune to the herbicide (i.e. Roundup Ready crops).

1 Comment »

  1. Would you be willing to share this photo of a monarch on Asclepias tuberosa for an article that I am putting together about monarchs? It will be about monarchs in the southern U.S. Thanks!

    Comment by Wendy — July 5, 2012 @ 11:39

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