Department of Biological Sciences, DePauw University, Greencastle, IN 46135, USA.
Both the larval and adult stages of Apollo butterflies are aposematic and reportedly distasteful to predators. The Small Apollo, Parnassius phoebus, was recently shown to sequester a cyanoglucoside, sarmentosin, from its hostplant (Sedum stenopetalum) in Washington State, USA. Over the past three summers, I have investigated the chemical ecology of P. phoebus and its host, Yellow Stonecrop (S. lanceolatum), in the Rocky Mountains. Colorado P. phoebus sequester significant amounts of sarmentosin from S. lanceolatum. Sarmentosin concentration of butterflies is one to two orders of magnitude greater than that of the plants. Male and female butterflies, however, do not differ significantly in the concentration of sarmentosin sequestered. Sarmentosin concentration of both plants and insects does vary significantly with altitude (2435m to 3535m). Organisms from lower elevations contain significantly more sarmentosin. Because sarmentosin is a nitrogenous defense, I have hypothesized that its production by plants should be limited by available nitrogen. Automobile emissions have resulted in increased rates of nitrogen deposition in the Front Range of the Rocky Mountains adjacent to Denver, Colorado. Plants and butterflies were sampled along the Colorado Front Range as well as across the Continental Divide in order to assess the effects of environmental pollution on the chemical interactions between insects and their hostplants. Future studies will investigate experimentally the relationship between nitrogen fertilization, sarmentosin production by S. lanceolatum, and sarmentosin sequestration by Apollos.