The structure of compound eyes in arthropods has been the subject of many studies, revealing important biological principles. Until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. By taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume electron microscopy, we present the first cellular-level reconstruction of the whole compound eye of an insect, the miniaturized parasitoid wasp Megaphragma viggianii . The compound eye of the female M. viggianii consists of 29 ommatidia and contains 478 cells. Despite the almost anucleate brain, all cells of the compound eye contain nuclei. As in larger insects, the dorsal rim area of the eye in M. viggianii contains ommatidia that are believed to be specialized in polarized light detection as reflected in their corneal and retinal morphology. We report the presence of three ‘ectopic’ photoreceptors. Our results offer new insights into the miniaturization of compound eyes and scaling of sensory organs in general.

Body size, especially in cases of extreme reduction, is an important characteristic that strongly determines the morphology, physiology, and biology of animals. Miniaturization is a widespread trend in animal evolution and one of the principal directions of evolution in insects. The superfamily Chalcidoidea has reached the peak of miniaturization among insects. This chapter contains a brief review of the consequences of miniaturization in Chalcidoidea and a discussion of the role of the smallest hymenopterans in studying miniaturization as an evolutionary phenomenon and their potential role in other areas of studies.

The structure of compound eyes in arthropods has been the subject of many studies revealing important biological principles. However, until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. Here, by taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume electron microscopy (vEM), we present the first cellular-level reconstruction of the whole compound eye of an insect, the extremely miniaturized parasitoid wasp Megaphragma viggianii . The compound eye of the female M. viggianii consists of 29 ommatidia and contains 478 cells. Despite the almost anucleate brain, all cells of the compound eye possess nuclei. Like in larger insects, the dorsal rim area (DRA) of the M. viggianii eye contains ommatidia that putatively specialize in the polarized light detection as reflected in their corneal and retinal morphology. We report the presence of three ‘ectopic’ photoreceptors. Our results offer new insights into the miniaturization of compound eyes and scaling of sensory organs in general.

The structure of compound eyes in arthropods has been the subject of many studies revealing important biological principles. However, until recently, these studies were constrained by the two-dimensional nature of available ultrastructural data. Here, by taking advantage of the novel three-dimensional ultrastructural dataset obtained using volume electron microscopy (vEM), we present the first cellular-level reconstruction of the whole compound eye of an insect, the extremely miniaturized parasitoid wasp Megaphragma viggianii . The compound eye of the female M. viggianii consists of 29 ommatidia and contains 478 cells. Despite the almost anucleate brain, all cells of the compound eye possess nuclei. Like in larger insects, the dorsal rim area (DRA) of the M. viggianii eye contains ommatidia that putatively specialize in the polarized light detection as reflected in their corneal and retinal morphology. We report the presence of three ‘ectopic’ photoreceptors. Our results offer new insights into the miniaturization of compound eyes and scaling of sensory organs in general.