Week 1: reading papers

My summer research started out with reading a ton of papers on all aspects of the monarch butterfly life cycle.  I thought I knew most of it pretty well after researching the monarch and milkweed interaction for three years, but there is always more to learn.  The idea behind my project is that there was a change in the monarch butterflies’ diet over the past century as prairie was replaced by farmland and eastern forests were cleared.  I hypothesize that they are now less chemically defended because their main food plant is Asclepias syriaca which contains low levels of weakly emetic cardenolides.  This may have led to an increase in mortality during their overwintering period due to greater numbers being eaten by birds.  In the process of writing a grant proposal to fund this project, I have read about 30 papers on monarchs and milkweed.

I read about land conversion in the US since the early 1900s and it’s horrifying; only tiny remnants of the original prairie still exist.  I learned that A. syriaca, usually called “common milkweed” was actually quite uncommon prior to the arrival of European colonists.  A. syriaca thrives in disturbed habitats such as agricultural fields and roadsides.  On the intact prairie, A. syriaca was limited to areas around animal burrows and other naturally disturbed areas.  While greater than 90% of monarch butterflies overwintering in Mexico today were reared on A. syriaca, before European style agriculture, the vast majority of monarchs fed on other milkweed species.  This has implications for modern conservation efforts.  A lot of attention is being given to the loss of common milkweed and how that may limit the number of monarch eggs laid.  In fact, A. syriaca is still more common today than it was in 1900.  Efforts to plant common milkweed may not be as effective in helping the monarch butterfly population as planting the higher cardenolide milkweed species that were abundant 100 years ago.

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