1-Octen-3-ol together with geosmin: new secretion compounds from a polydesmid millipede, Niponia nodulosa.

The small millipede Niponia nodulosa (Polydesmida: Cryptodesmidae) emits an earthy smell when disturbed. This smell was obtained from hexane extracts from both sexes at the sixth and seventh instars and adult stages, and was found by GC/MS analyses to be composed of two compounds, 1-octen-3-ol as the major component and geosmin as the minor component. This is the first report of these compounds in secreted substances from millipedes. As they showed little repellent activity against foraging ants in bioassays, their biological function as defensive allomones was not clearly elucidated. However, both compounds provoked negative chemotaxis of conspecific millipedes in a Y-tube olfactometer, especially 1-octen-3-ol, which was active at a dose equivalent to the content of a single millipede. Such biological activity suggests that this compound is involved in intraspecific communication in this millipede and may play a role as an alarm pheromone.