Importance of floral phenology and florivory for Tetraopes tetraophthalmus (Coleoptera: Cerambycidae): Tests at the population and individual level

Abstract

We examined the phenological relationship between the abundance of Tetraopes tetraophthalmus (Forster) and flowers of its host plant Asclepias syriaca and tested the hypothesis that flowers are an important nutritional resource relative to foliage. Over 3 yr, we found that the abundance, emergence, immigration, and emigration of beetles in natural populations were positively related to milkweed flowering on individual patches. In experiments where inflorescences were removed from sections of milkweed patches, beetles showed a strong positive response in abundance to the presence of milkweed flowers. At the individual level, the role of florivory versus feeding on foliage was equivocal. Beetles showed no preference for flowers versus foliage. Digestibility of flowers was greater than foliage, but the conversion of ingested material showed no difference for adult beetles fed flowers versus foliage. Relative and absolute differences between beetles fed flowers versus foliage varied between years. In 1996, beetles fed a diet of flowers produced significantly fewer larvae than beetles fed foliage alone, but showed no difference in lifespan. In 1997, a diet of flowers alone produced both longer lifespans and greater reproductive output than a diet of flowers and foliage. A nutritional hypothesis did not consistently explain the population level response to milkweed flowers.