Milkweed Research Paper

Each year, monarch butterflies migrate thousands of kilometres though North America.The larva of these butterflies eat only milkweed; the availability of which is decreasing due to urbanization, herbicide use, and pesticide use. In the past 20 years, 90% of the monarch butterfly population had died (2). The model I created shows four different pieces of information shown on top of a map of north America. The translucent blue coloured area represents the general living area of the Western and the Eastern migratory North American monarch butterfly populations (8). The translucent red coloured area represents the areas of the United States of America (U.S.) with recorded glyphosate spraying; a commonly used pesticide that kills milkweed (3). The

According to John M. Pleasants and Karen S. Oberhauser (10) the milkweed destiny decreased in agricultural fields by 81% from 1999 to 2010. This is largely the result of glyphosate spraying (3) (10). Comparatively, the milkweed destiny in non-agricultural fields only decreased 31% (10). Pleasants and Oberhauser found a significant decrease in monarch egg density with an estimated decrease of 81% in the Midwest on agricultural milkweed (10). However, they did not find a significant change in monarch egg destiny on non-agricultural milkweed in the Midwest (10). In addition to being a concerning fact in itself, this data demonstrates the correlation of pesticides to the loss of agricultural milkweed. It is clearly visible that a vast area of the U.S. cropland is sprayed with glyphosate, much of which interrupts monarch migratory paths. From 1992-2012, 2.6 billion pounds of glyphosate was sprayed in the U.S. alone (11). Glyphosate is also the widest used pesticide in the world, despite the damage it does to milkweed and the potential carcinogenic effects on humans (11) (12) (13)

They point out that monarchs seem to prefer agricultural milkweed and give a few possibilities as to why. One possibility is that the milkweed in agricultural fields is of a generally higher quality because of the high nitrogen concentrations in the soil (10). Another possibility that they suggest is the monoculture background of the fields allow for the chemical signal from the milkweed to be located more easily by the female monarchs (10). They also point out the importance of roadside milkweed, which accounts for 20% of the milkweed available to monarchs (10). By avoiding mowing roadsides or spraying them with herbicides it could be extremely beneficial to the monarch