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1 August 2016 Monarch Butterflies Use Regenerating Milkweeds for Reproduction in Mowed Hayfields in Northern Virginia
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The effects of mowing milkweeds in areas visited by monarch butterflies (Danaus plexippus L., Nymphalidae) were studied by counting the eggs and larvae on regenerating common milkweeds (Asclepias syriaca L., Apocyanaceae) in five adjacent mowed hayfields in northern Virginia in late summer 2015. At the same time monarch larvae were counted on mature senescent common milkweeds in unmowed areas adjacent or near to the mowed hayfields. Milkweeds supported populations of immature monarchs in both habitat types with initially many eggs and early instars found on regenerating plants in the mowed hayfields while late instars dominated the unmowed older milkweeds. As September proceeded, the censuses revealed an increase in the numbers of late instars on the mowed regenerating milkweeds whereas the abundance of larvae declined sharply on the older senescing milkweeds, many of which had lost all or most of their leaves. The study showed that late season mowing of hayfields provided adult female monarch butterflies with rejuvenated resources for reproduction during a time when senescent milkweeds were becoming unsuitable for the monarch larvae. Our findings have implications for managing land in ways to benefit monarchs and for mitigating the widespread decline of milkweeds, although the research raises several caveats and more needs to done to measure the fitness of monarch adults that are produced late in the flight season of the butterfly.

John Alcock, Lincoln P. Brower, and Ernest H. Williams Jr. "Monarch Butterflies Use Regenerating Milkweeds for Reproduction in Mowed Hayfields in Northern Virginia," The Journal of the Lepidopterists' Society 70(3), 177-181, (1 August 2016).
Received: 30 October 2015; Accepted: 11 January 2016; Published: 1 August 2016

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