Species- and caste-determined mandibular gland signals in honeybees (Apis)

Queens and workers of five honeybee species (Apis mellifera, A. cerana, A. dorsata, A. florea, and A. andreniformis) were analyzed for their mandibular gland components. In A. mellifera, the queen mandibular pheromone consists of 9-hydroxy- and 9-keto-2(E)-decenoic acids (8-HDA and ODA), methyl p-hydroxybenzoate (HOB), and 4-hydroxy-3-methoxyphenylethanol (HVA), and is responsible for retinue attraction, among other functions. In retinue bioassays with workers of A. cerana (whose queens lack HVA), ODA, 9-HDA, and HOB were sufficient to elicit maximal retinue behavior. This suggests that the known queen mandibular pheromone components detected in mandibular glands of A. cerana queens constitute the functional queen mandibular pheromone in this species. Both castes of A. mellifera produce 10- and 8-carbon acids that are functionalized at the last position in the chain, and these are the predominant compounds found in worker mandibular glands. Workers of the other species also had these compounds, along with 9-HDA and ODA that are normally not present in A. mellifera worker glands. Queens and workers of each species had a unique combination of mandibular compounds. The aromatic compounds were characteristic of queens from the cavity-nesting species, A. mellifera (HOB and HVA) and A. cerana (HOB). These two species also had more pronounced differences in the mandibular blends of queens and workers than the open-nesting species, A. dorsata, A. florea, and A. andreniformis. Our results indicate that the more derived cavity-nesting species of Apis have evolved greater caste-specific differences between queens and workers and a higher number of queen pheromone components, compared to the open-nesting species.