A selfish function of a "social" gland? A postpharyngeal gland functions as a sex pheromone reservoir in males of the solitary wasp Philanthus triangulum.

The postpharyngeal gland (PPG) has long been assumed to be restricted to ants, where it mainly functions in the maintenance of social integrity. Recently, a PPG has been described in both sexes of a solitary digger wasp, the European beewolf, Philanthus triangulum (Hymenoptera, Crabronidae). Female beewolves use the contents of their PPG to embalm their honeybee prey to delay microbial growth. Here we show that in male beewolves, the PPG serves as a reservoir of the pheromone used to scent-mark their territories. Gas chromatography-mass spectrometry (GC-MS) analysis of PPG contents identified 55 substances including long-chain aliphatic hydrocarbons, and 13 substances with functional groups. The composition was consistent with the composition of the marking pheromone of male European beewolves described earlier. Comparisons of the PPG contents, and total-head extracts showed a strong congruency, suggesting that total-head extracts can be used for the analysis of marking secretion in beewolves. Furthermore, we found a dimorphism in the composition of the PPG contents, based on significant differences in the proportions of seven compounds between the two morphs.