Multiscale head anatomy of Megaphragma (Hymenoptera: Trichogrammatidae).

Methods of three-dimensional electron microscopy have been actively developed recently and open up great opportunities for morphological work. This approach is especially useful for studying microinsects, since it is possible to obtain complete series of high-resolution sections of a whole insect. Studies on the genus Megaphragma are especially important, since the unique phenomenon of lysis of most of the neuron nuclei was discovered in species of this genus. In this study we reveal the anatomical structure of the head of Megaphragma viggianii at all levels from organs to subcellular structures. Despite the miniature size of the body, most of the organ systems of M. viggianii retain the structural plan and complexity of organization at all levels. The set of muscles and the well-developed stomatogastric nervous system of this species correspond to those of larger insects, and there is also a well-developed tracheal system in the head of this species. Reconstructions of the head of M. viggianii at the cellular and subcellular levels were obtained, and of volumetric data were analyzed. A total of 689 nucleated cells of the head were reconstructed. The ultrastructure of M. viggianii is surprisingly complex, and the evolutionary benefits of such complexity are probably among the factors limiting the further miniaturization of parasitoid wasps.

Wing morphology in featherwing beetles (Coleoptera: Ptiliidae): Features associated with miniaturization and functional scaling analysis.

The wings of Ptiliidae, the coleopteran family containing the smallest free-living insects, are analyzed in detail for the first time. A reconstruction of the evolutionary sequence of changes associated with miniaturization is proposed. The wings of several species are described using light microscopy and scanning electron microscopy. The morphology and scaling are analyzed in comparison with larger representatives of related groups. The wings of all studied ptiliids show some degree of ptiloptery (feather-like shape, typical for extremely small insects). In larger ptiliids the wing contains at least five veins, has a wide blade, and bears a marginal fringe of 200-300 setae; in the smallest species it has three veins or fewer, a narrow blade, and about 40 setae along the margin. The setae are brush-like; peculiar outgrowths, denser towards the apex, increase the effective diameter of the setae. Morphometric analysis shows that the geometry of the wings and their elements strongly differs from those of other staphyliniform beetles, suggesting that the aerodynamics of the feather-like wings may also differ distinctly from the usual pattern.