LAUSR

Monarch populations have declined precipitously over the past decades, largely due to the loss of their breeding host plant, milkweed. One mitigation strategy is to plant milkweed along rights-of-ways. However, many rights-of-ways undergo routine mowing, which can result in egg, caterpillar, and chrysalis mortality. To minimize this risk, it is critical to time mowing activity to avoid the peak breeding activity of monarchs. In this study we used community science data to define breeding patterns and timing of monarch breeding throughout the United States and Canada. We identified four breeding patterns: (1) year-round, (2) spring-only, (3) summer, and (4) disjunct breeding. Year-round and disjunct breeding were concentrated around the Gulf of Mexico, including Florida, and the southern United States, respectively. As expected, we found that monarch breeding was later with increased latitude but with some longitudinal variation; for summer breeding regions, breeding occurred earlier in the western portion of the study area relative to the east, but the end of breeding was later in the east relative to the west, resulting in breeding seasons of similar duration. Additionally, in the east, breeding occurred later along the Appalachian Mountains. We suggest adapting our findings into mowing practices that benefit monarchs while considering the life histories of milkweed and the broader insect community. Implications for insect conservation. Mowing and other maintenance activities in habitat where milkweed is present can be detrimental to monarch breeding. Our analysis provides guidance to minimize monarch mortality and loss of milkweed during peak breeding periods.