The decline of monarch butterfly populations is getting much attention in the northern plains, but lately, there’s doubt about the severity of the decline and whether it’s caused by the disappearance of milkweed, the only plant on which the butterfly lays eggs. Iowa State University Researcher John Pleasants says monarch populations in the Midwest may appear stable because counts are taken in open areas where butterflies can find milkweed.

Pleasants says the milkweed is being killed off by herbicides.

Pleasants estimates at least one-point-six-billion new milkweed seeds need to be planted in the Midwest to restore the monarch population. He’s now working on the best techniques for adding more milkweeds to the landscape.