The postpharyngeal gland in solitary Hymenoptera

We found that both sexes of the solitary crabronid wasp P. triangulum possess a postpharyngeal gland. In male beewolves the postpharyngeal gland functions as reservoir of the pheromone, that males apply onto surfaces in their territory to attract receptive females.

In female P. triangulum the postpharyngeal gland harbors a secretion that is used for a unique method of prey preservation. Before female beewolves oviposit on their paralyzed prey bees, they virtually mantle the bees with large amounts of a secretion from their postpharyngeal glands. This embalming of the prey with mostly unsaturated hydrocarbons reduces water condensation on the surface and in this way indirectly hampers the growth of mold fungi under moist conditions. Under dry conditions the embalming of the prey bees decreases the evaporative water loss of the prey. The secretion from the postpharyngeal gland thus protects the larval provisions from adverse physical conditions so that they stay fresh and consumable. We could show that prey embalming by female P. triangulum qualifies as parental investment, as it brings about  benefits with regard to offspring survival but also entails costs in the form of reduced ability to invest in future offspring.

Females of the two South American beewolf species Trachypus boharti and Trachypus elongatus also possess postpharyngeal glands, which are very similar to the one of P. triangulum with regard to morphology, ultrastructure and chemical content. We could show that T. elongatus also embalms its prey, the stingless bee Trigona hyalinata, with mostly unsaturated hydrocarbons.

In the Juwelwasp A. compressa both sexes possess postpharyngeal glands. These glands are much smaller than those of P. triangulum and the function is as yet unknown. We are currently screening other hymenopteran species to learn more about the phylogenetic distribution of the postpharyngeal gland, its function in other species, and its possible role in the evolution of sociality.




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Herzner G, Kaltenpoth M, Poettinger T, Weiss K, Koedam D, Kroiss J, Strohm E (2013) Morphology, chemistry and function of the postpharyngeal gland in the South American digger wasps Trachypus boharti and Trachypus elongatus. PLoS ONE 8(12): e82780. doi:10.1371/journal.pone.0082780.

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