Host plant utilization and iridoid glycoside sequestration byEuphydryas anicia (Lepidoptera: Nymphalidae).

The iridoid glycoside content of individual adultEuphydryas anicia butterflies from two Colorado populations was quantitatively determined. At one site (Red Hill), larval host plants wereCastilleja integra andBesseya plantaginea, while at the other site (Cumberland Pass) a single host plant,B. alpina, was used. At Red Hill, macfadienoside and catalpol were sequestered, while at Cumberland Pass, catalpol and aucubin were sequestered. Artificial diet studies showed that larvae hydrolyzed a major iridoid ofB. plantaginea, 6-isovanilIylcatalpol, to catalpol (which was sequestered) and isovanillic acid (which was excreted). Large year-to-year and individual variation in butterfly iridoid content was established as was a female-male difference in macfadienoside vs. catalpol content. Larval host plant distributions and numbers were determined at Red Hill for two years and compared with changes in butterfly populations and sequestered iridoids.