Mushroom bodies in Hymenoptera

Mushroom bodies are a morphologically very distinct brain center in insects, which are given shape by many thousands of morphologically similar cells [about 340 000 in the honey bee; Witthöft, 1967]: the Kenyon cells. In pterygote insects the Kenyon cells have a dendritic region which together with their cell bodies form the calyx of the mushroom bodies. The neurites leave the calyx to form the peduncle until they bifurcate, with one branch of each cell leading towards the front of the brain, constituting in their entirety the alpha or vertical lobe. The second branch leads towards the midline of the brain, contributing to the beta or median lobe.In Hymenoptera within the calyx, three concentric zones can be discriminated using conventional staining methods: lip, collar, and basal ring. With an anterograde tracer the distribution of visual and olfactory input reveals even more partitions [Gronenberg, 2001]. Afferents from the optic lobes terminate in the collar and basal ring, whereas olfactory sensory information from the antennal lobes is brought to the lip and also to the basal ring [Gronenberg, 2001]. The function of mushroom bodies is still not clear, but most evidence supports their role in olfactory learning and memory [Erber et al., 1980; Heisenberg et al., 1985; Connolly et al., 1996]. In addition, functions such as place memory and motor control [Mizunami et al., 1998], and context dependent filtering [Li and Strausfeld, 1999] have been proposed for the mushroom bodies.

Comparison of the morphology of the mushroom bodies of the honey bee Apis mellifera and of vespid wasps. In vespid wasps the mushroom body morphology is more variable than in other Hymenoptera. In these reconstructions of mushroom bodies the lip is shown in red, the collar in yellow, the basal ring in green. The peduncle is cyan, the alpha-lobe blue and the beta-lobe purple. Compare the different morphologies of especially alpha and beta lobes of the different vespid wasps. The phylogenetic tree indicates the phylogenetic relationship between the investigated species. The wasp species are from all of the six subfamilies of vespid wasps: the euparagine, masarine (pollen wasps), eumenine (potter wasps), stenogastrine (hover wasps), polistine (paper wasps) and vespine wasps (hornets and yellowjackets).

some old mushroom body literature