The winter cherry bug colonizes the Duboisia leichhardtii tree, which is a rich source of scopolamine. It consumes the tropane alkaloids atropine and scopolamine. Quantitative analysis revealed that the ratio of scopolamine to atropine in the winter cherry bug (0.46) was far from that found in the leaves of the host plant (7.20). To elucidate whether the winter cherry bugs selectively excrete or decompose scopolamine, they were fed scopolamine and/or atropine together with sucrose. They took up scopolamine as well as atropine, and converted scopolamine into atropine.