The postpharyngeal gland (PPG) was thought to be restricted to ants where it serves a crucial function in the generation of the colony odour. Recently, head glands that closely resemble the PPG of ants were discovered in females of a solitary digger wasp, the European beewolf. The function of this gland necessarily differs from ants: beewolf females apply the secretion of their PPG onto the bodies of paralysed honeybees that serve as larval provisions in order to delay fungus growth. Since ants and digger wasps are not closely related, the occurrence of this gland in these two taxa might either be due to convergent evolution or it is a homologous organ inherited from a common ancestor. Here we test the hypothesis that the PPGs of both taxa are homologous by comparing characteristics of chemical composition and physiology of the PPG of beewolves and ants. Based on reported characteristics of the PPG content of ants, we tested three predictions that were all met. First, the PPG of beewolves contained mainly long-chain hydrocarbons and very few compounds with functional groups. Second, the composition of hydrocarbons in the beewolf PPG was similar to that of the hemolymph. Taking the structure of the gland epithelium and the huge requirements of beewolf females for gland secretion into account this result suggests that the content of the PPG is also sequestered from the hemolymph in beewolves. Third, the chemical composition of the PPG and the cuticle was similar in beewolves since cuticular hydrocarbons derive either from the hemolymph or the PPG. Taking the considerable morphological similarities into account, our results support the hypothesis of a homologous origin of the PPG in beewolves and ants.

中文翻译：

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独居黄蜂的咽后腺与蚂蚁同源吗？来自化学和生理学的证据

咽后腺 (PPG) 被认为仅限于蚂蚁，它在产生菌落气味方面发挥着关键作用。最近，在独居的欧洲蜂狼的雌性身上发现了与蚂蚁 PPG 非常相似的头部腺体。这种腺体的功能必然不同于蚂蚁：雌性蜂狼将其 PPG 的分泌物涂抹在麻痹蜜蜂身上，作为幼虫的食物，以延缓真菌的生长。由于蚂蚁和挖掘黄蜂的亲缘关系并不密切，因此这两个分类群中出现这种腺体可能是由于趋同进化造成的，也可能是从共同祖先遗传的同源器官。在这里，我们通过比较蜂狼和蚂蚁 PPG 的化学成分和生理学特征来检验两种分类群的 PPG 同源的假设。根据报告的蚂蚁 PPG 含量的特征，我们测试了三个都满足的预测。首先，蜂狼的 PPG 主要含有长链烃，极少含有官能团的化合物。其次，beewolf PPG 中碳氢化合物的组成与血淋巴相似。考虑到腺上皮的结构和雌性蜂狼对腺体分泌的巨大需求，这一结果表明 PPG 的含量也与蜂狼的血淋巴隔离。第三，PPG 和角质层的化学成分在蜂狼中是相似的，因为表皮碳氢化合物来自血淋巴或 PPG。考虑到相当大的形态相似性，我们的结果支持蜂狼和蚂蚁中 PPG 同源起源的假设。