Host plant scents attract rolled-leaf beetles to Neotropical gingers in a Central American tropical rain forest

Leaf volatile chemicals are known to reduce herbivory rates by repelling or intoxicating insect herbivores and by attracting the predators and parasitoids of herbivores. However, leaf volatiles may also be used by insect herbivores as cues to locate their host plants. Leaf volatiles are suggested to be important host search cues for herbivores in structurally complex and diverse habitats, such as tropical rain forests. A group of insect herbivores, the rolled-leaf beetles (Coleoptera: Chrysomelidae: Hispinae), have maintained a highly specialized interaction with Neotropical gingers (Zingiberales) for ca. 60 million years. In this study, we explored chemical attraction to host plants under controlled laboratory conditions, using four sympatric rolled-leaf beetle species, Cephaloleia dorsalis Baly, Cephaloleia erichsonii Baly, Cephaloleia fenestrata Weise, and Cephaloleia placida Baly. For each beetle species, we investigated (i) whether it was repelled or attracted by leaf scents produced by four host and four non-host plant species, including Neotropical gingers in the families Marantaceae, Costaceae, and Zingiberaceae; and (ii) its ability to use scents to detect its host plant. We found that rolled-leaf beetles can detect and are attracted by leaf volatiles from both host and non-host gingers. Additionally, when beetles were simultaneously exposed to leaf volatiles from host and non-host plants, three rolled-leaf beetle species were significantly more attracted by volatiles from their host plants than from non-hosts. Only one of the beetle species was not able to discriminate between host and non-host scents.