Where is it that they are doing the worst?” and can we then take that information and infer what the problem might be.ĬURWOOD: So, of course, we want you to give us the answer.ĪGRAWAL: Yeah. By putting those different datasets together we were able to ask, “where is the weak point in the annual migratory cycle. We're very very fortunate to have many different datasets where citizen scientists and conservation organizations have been tracking the monarch populations, and it's one of the wonderful resources where people had the foresight 25 years ago to start these monitoring programs. From there, their offspring, or the next generation, flies up to the Midwest and the northeastern USA and Canada where they breed for two to three more generations. So in the fall they fly all the way down to Mexico, rest there for four months, fly back to the USA and then lay eggs in Texas and Oklahoma. (Photo: Luna Sin Estrellas, Flickr Creative Commons 2.0)ĪGRAWAL: What we did was we really tried to put the pieces together, and what I mean by that is the monarch butterfly has a very complex annual migratory cycle. Over winter, monarchs usually coat the sky in the valleys of Michoacán, Mexico.

Nonetheless, we were compelled to try to take a rigorous look at the data that are out there to ask the question, is that what's really going on. It certainly seemed quite logical that milkweed limitation could be playing a role in the population trends and the downward spiral of the monarch butterfly. It comes from a team led by Anurag Agrawal, a professor of Ecology and Evolutionary Biology at Cornell University.ĪGRAWAL: Milkweed has been declining, certainly in the Midwestern USA where agriculture is most prominent, and with the increased use of herbicides and genetically modified crops that are tolerant of those herbicides, the amount of milkweed in those agricultural fields has declined.

And this new study questions a key conventional wisdom about the role of pesticides and milkweed in the decline in Monarch numbers. CURWOOD: Hot on the heels of that legal push to protect this iconic insect comes a study that throws new light on the many threats that face the butterflies on their multi-generational migration from Mexico to the US and Canada and back.

Monarchs and Milkweed by Anurag Agrawal