Reply to Wepprich and Ries et al.: Alternative methods do not provide support for the contribution of GM crops to monarch declines

We are pleased to see Wepprich (1) and Ries et al. (2) engaging with the museum records data presented in our original study (3). One of the strengths of digitized specimen data is that its portability allows precisely this kind of reanalysis. The main point of our original study was that genetically modified (GM) crops were unlikely to be an important factor in monarch declines because milkweed and monarchs began their declines decades before the introduction of GM crops (3). Both Wepprich (1) and Ries et al. (2) propose alternative methodologies for using museum data to calculate monarch butterfly abundance over time, and both suggest that the currently available data are insufficient to estimate the true monarch abundance trends over the past century. If Wepprich (1) and Ries et al. (2) are correct that monarch abundance over the 20th century is still unknown (we discuss the specifics of their proposals below), this does not change our primary conclusion. Farming of GM crops has been proposed to impact monarch populations by … [↵][1]1To whom correspondence may be addressed. Email: jrpuzey{at}wm.edu. [1]: #xref-corresp-1-1