Metamorphosis of the Central Nervous System in Habrobracon hebetor (Hymenoptera, Braconidae)

The structure of the central nervous system (CNS) of Habrobracon hebetor Say 1836 during the development from prepupa to imago was studied using histological methods and three-dimensional computer modeling. The metamorphosis of the CNS in H. hebetor largely coincides with the previously described changes in the related groups of Hymenoptera. During development, the thoracic and abdominal ganglia of the nerve cord converge, the concentration of which reaches a maximum by the imago. The most noticeable changes in the CNS occur at the pupa stage I, when a sharp increase in the volumes of the cell cortex and neuropil in the CNS ganglia, an increase in the relative volume of the ganglia, and an increase in the size of nerve cells are observed. The increase in the cell cortex of the ganglia is followed by its decrease by the imago stage, while the volume of the neuropil is significantly increased by the time the adult individual appears. An increase in the volumes of the key neuropil centers occurs throughout development from prepupa to imago. After a rapid increase in the size of nerve cells at the beginning of pupal development, it is decreased, with the average size of nerve cells in the imago being the same as in the prepupa. The number of nerve cells during pupal development is first increased, compared to decreased at the imaginal stage, but not as much as in miniature Hymenoptera.