Histomorphological changes in the brain and nerve cord of the indian wasp Polistes hebraeus fabr. (Hymenoptera : Vespidae) during metamorphosis

Abstract

1. The early larva has a bilobed brain and a suboesophageal ganglion in the head; 1 ganglion in each thoracic and 8 ganglia in abdominal segments. 2. The brain of mature larva shows differentiation of proto-, deuto-, and tritocerebrum internally but not externally. 3. In the early pupal period the 3 optic lobes differentiate and forward migration of the suboesophageal ganglion and the 1st and 2nd abdominal ganglia and backward movement of 6th abdominal ganglion are noted. 4. In the fully formed pupa the suboesophageal ganglion lies very close to the brain. The mesothoracic, 1st abdominal and 2nd abdominal ganglia fuse with the metathoracic to form a thoracoabdominal ganglionic mass. 5. Optic lobes and epidermal eye primordia contribute in the formation of the compound eyes. 6. The 7th abdominal ganglion fuses with the terminal ganglion and the 6th abdominal ganglion of the larva (4th abdominal of adult) comes very close to the terminal ganglion (Fig. 1). 7. Partial degeneration of neurilemma and neural lamella and thickening of the connective tissue sheath covering the nerve cord is noted during the pupal period. 8. Enlargement of larval nerve cells is noted during the pupal period, but cell division is not seen. 9. In late pupa the ocellar lobes develop on the anterolateral sides of the central body; deutocerebrum becomes differentiated with an outer cortex and inner medulla. 10. Ellipsoid body appears on the posterior part of the central body. Corpora pedunculata become enormously developed with a large inner root placed posteriorly to the central body and gradually the brain assumes the adult form.