Demarchushsui (Coleoptera, Chrysomelidae, Galerucinae, Alticini), a new species from Taiwan, with notes on immatures and biology.

A new species of the little-known genus Demarchus Jacoby was discovered at Pilu, East Taiwan, and is here described as Demarchushsui sp. nov . The larvae and adults utilise showy mistletoes as food plants. Their remarkable biology is described in detail, including egg deposition and leaf mining behaviour. Their biology is compared with that of other members of the genus.