Metamorphosis of the central nervous system of Megaphragma viggianii (Hymenoptera: Trichogrammatidae).

Miniaturization, egg parasitism, and the presence of anucleate neurons in adults can greatly affect the quantitative and qualitative characteristics of the central nervous system (CNS) during metamorphosis. Such features have already been shown for the brain of Megaphragma, but have not been examined for other parts of the nervous system. Using histological methods, confocal microscopy, and three-dimensional computer modeling, we describe the structure of the CNS during the pupal development of Megaphragma viggianii (Hymenoptera: Trichogrammatidae). The processes of compactization and oligomerization of the ganglia continue throughout development. The absolute volume of the CNS decreases from the prepupa to the adult by a factor of more than 5. The main reason for this is the reduction in the volume of the cell body rind due to the lysis of cell bodies and nuclei, which occurs in each ganglion of the CNS. In the pharate adult, the CNS consists of an average of 13 000 nerve cells, but only about 400 nuclei remain in adult. The main changes in the course of CNS development, including the lysis of neuron nuclei, occur in all ganglia almost synchronously. The results obtained expand our understanding of the development of the CNS in parasitoid wasps and the phenomenon of anucleate neurons.