A study of the phenology, breeding system, and insect pollinators of Diervilla lonicera demonstrated the flowers to be protogynous, self-incompatible, non-apomictic, and adapted for pollination by bumble bees and hawkmoths. The style and filaments increased in length during anthesis. The stigmas were very receptive for up to 48 hr after the start of anthesis. A color change in the corolla was linked with a decrease in flower visitation by bumble bees (Bombus vagans and B. terricola). Adults and larvae of the hawkmoth, Hemaris diffinis are associated with the plant in four widely separated localities. The flowers open late in the day, but no nocturnal pollinators were observed. Nocturnal hawkmoth pollination may occur in the southern part of the plant’s range.