New host records are reported for Campiglossa snowi (Hering), Tephritis leavittensis Blanc, and Trupanea nigricornis (Coquillett) on Arnica chamissonis Less. and C. snowi on Arnica mollis Hook. Campiglossa snowi was the only fruit fly reared from A. chamissonis from 3 different populations from the Kenai Peninsula, Alaska, over 5 sample years. A total of 1114 specimens of C. snowi were reared from the flower heads of 337 plants averaging 5 flower heads per plant. Seed damage from fly larvae ranged from 0% to 54.8% per capitulum, with an overall average of 18.3% across all years and between 3 sites on the Kenai Peninsula. Infestation rates for individual capitula and entire plants averaged 56.4% and 79.0%, respectively, across all years and sites. Fly abundance was not consistent from year to year, but peaked during 2010, with substantially lower values in years preceding and following the peak. Campiglossa snowi individuals reared from flower heads at additional sites and across multiple states expand the species' known distribution range.