Although glyphosate-driven milkweed loss remained one possible explanation, other theories emerged over time. Since then, monarch populations have continued to fall. The prevailing theory during that period has been that the loss of milkweed from agricultural areas was responsible for the severe declines. Farmers grew crops that were engineered to be resistant to glyphosate, allowing them to apply the chemical widely, decimating milkweed plants that are the sole host and food source for monarch caterpillars. The mid-1990s through the mid-2000s saw the most dramatic decline, coinciding with a period when glyphosate weed killers became hugely popular in the agricultural industry. Since the mid-1990s, though, there has been a dramatic decline in their population, with worst-case estimates projecting that the current population is a mere 20% of what it was just a few decades ago.Ī monarch butterfly sits atop flowering swamp milkweed in a Michigan garden. and southern Canada every year - with summer layovers in Michigan and other U.S. The eastern population of monarchs migrates between Mexico and the eastern half of the U.S. Understanding the monarch decline and doing what we can to reverse it is important not just for preserving biodiversity, but also because insects are prolific pollinators. “We did this study not just to say what’s causing changes in the monarch butterfly population, but also learn how we can make it better.” But in understanding the reasons why a species is declining, there is also a message of hope: there’s something we can do about it,” said Zylstra. Zylstra is a postdoctoral researcher in the Department of Integrative Biology and the Ecology, Evolution and Behavior Program, both in MSU’s College of Natural Science. “What we do is develop models to understand why monarchs are declining and what’s happening to biodiversity in general,” said Erin Zylstra, the study’s lead author. Erin Zylstra, an MSU postdoctoral research associate

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