Beer-flavoring compounds guide insects

The compounds that give beer some bitter flavor notes also show up in garden flowers–but with more sober jobs.

A Hypericum flower that looks plain yellow (above) contains pigments that, in ultraviolet light (below), darken its center and buds. Eisner


Chemical ecologist Thomas Eisner of Cornell University found some of the bitter beer compounds, called DIPs for dearomatized isoprenylated phloroglucinols, in flowers of six species of the genus Hypericum. To bees’ ultraviolet-sensing eyes, the compounds create dark markings on the blooms. Scientists already knew that pigments, called flavonoids, created bee-visible markings on flowers, but the DIPs came as a surprise.

Eisner found the compounds to be especially concentrated in the flowers’ reproductive structures, such as the wall around the ovary. Could DIPs be doing double duty by deterring nibbling insects? To find out, Eisner and his colleagues offered paper wafers saturated with DIPs to caterpillars of the moth Uthesia ornatrix. They barely touched it, compared with DIPs-free paper, which they ate up. Moreover, several of the insects that did eat the DIPs-treated paper died during the tests.

DIPs are the first class of flower pigments known to double as protective compounds, according to a report by Eisner and a colleague that is scheduled to appear in the Nov. 20 Proceedings of the National Academy of Sciences.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.