Evaluation of the Alkaloid Secretions within the Millipede Brachycybe and Their Pheromone Properties

Brachycybe is a genus of the millipede subterclass Colobognatha, a group that exhibits rare social characteristics, including species aggregations and male brood care. Although it has been hypothesized that alkaloid-based defensive secretions may also function as pheromones, no studies have examined these traits. Here, we evaluated the chemical secretions of six species, two of which had not been previously studied, and conducted Y-tube pheromone assays. Chemical investigations elucidated the structures of three new metabolites: hydrogosodesmine acid (6), homo-hydrogosodesmine acid (7), and buzonamine acid (8). Y-tube pheromone assays revealed that Brachycybe producta is significantly attracted to conspecifics (p = 0.0428) and is deterred by a different species of alkaloid-producing millipede (p = 0.0161). The former assay was repeated using a mixture of the crude (p = 0.0428) and purified (p = 0.0433) chemical defense secretion fromB. producta. This study provides the first evidence that colobognath millipede chemical secretions serve both defensive and pheromone roles.