Functional morphology of the maxillary and propharyngeal glands of Monomorium pharaonis (L.)

•The maxillary gland opens at the base of the maxillary stipes and consists of 4 secretory cells.•The propharyngeal gland opens into the pharyngeal atrium and consists of 16 secretory cells.•The maxillary gand cells contain few cytoplasmic components whereas, the propharyngeal gland cells have abundant rER.•Both glands are largest in queens but they are not linked with reproduction.•Both glands are paired without reservoir but with a pouch where secretion can be stored temporarily.

The maxillary and propharyngeal gland of all 3 castes of Monomorium pharaonis were examined with light and electron microscopy. Although both glands possess a pouch in which secretion can be stored temporarily, a proper reservoir is lacking. The paired maxillary gland opens at the base of the maxilla and consists of 4 secretory cells, which are smaller in workers as compared to queens and males. A digestive role is unlikely as the gland is not directly linked to the digestive system and the amount of rER is negligible. The propharyngeal gland consists of 2 clusters of 16 secretory cells, which open in the pharyngeal atrium through a duct. Secretory cells are smallest in males. Two types of endoplasmic vesicles are observed around the end apparatus, suggesting a release of at least 2 substances. High levels of rER indicate the production of digestive enzymes as one of its functions. No differences between mated versus virgin queens were observed for both glands. Further experiments on chemical and behavioural essays can improve our understanding of the role of both glands in the ant colony. Literature on this topic is very inconsistent. We provide a survey to unravel this chaotic nomenclature issue.