The diversification of Hymenoptera took place in the Cretaceous and the gland may have developed at about this time (200 million years ago) as it is present in all three groups of Apocrita, the wasps, bees and ants.
The gaster is the bulbous posterior portion of the metasoma found in Apocrita Hymenoptera (bees, wasps and ants).
In apocritan Hymenoptera (wasps, bees and ants), the metasoma consists of the second abdominal segment (which typically forms a petiole) and those segments posterior to it, and is often called the gaster rather than referring to it as the "abdomen"; in these insects, the first abdominal segment is called the propodeum and is fused to the thorax.
In the suborder Apocrita of the Hymenoptera, the first abdominal segment is fused to the metathorax, and is then called the propodeum.
Fossils have been reported from the Lower Jurassic of Grimmen (Lower Toarcian, Germany) and the Middle Jurassic of Daohugou (China), which display a mixture of characters associated with Orussoidea and with basal Apocrita, thus it is impossibly to classify these specimens which one of these clades.
In the Apocritan Hymenoptera, the first abdominal segment is fused to the metathorax, where it forms a structure known as the propodeum.