Anatomical changes of the central nervous system during metamorphosis in Pieris rapae crucivara Boisduval (Lepidoptera : Pieridae)

Abstract

The larval central nervous system (CNS) of Pieris rapae crucivora Boisduval (Lepidoptera : Pieridae) consists of the brain, 12 ganglia and the connectives. During metamorphosis, connective shortening and ganglionic fusion occur in 3 phases. In the 1st phase, from full-grown larva to newly emerged (0-day) pupa, each connective between the ganglia and the brain shortens, and the overall length of the CNS decreases to 60% that of the full-grown larva. In the 2nd phase, from 0-day pupa to 3-day pupa, some ganglia move and the associated connectives shorten or lengthen with slight shortening of the overall length of the CNS. The subesophageal ganglion moves anteriorly to just beneath the brain. The meso- and metathoracic ganglia and the 1st and 2nd abdominal ganglia move anteriorly and fuse into a pterothoracic ganglion. The 6th, 7th, and 8th abdominal ganglia fuse into the last abdominal ganglion. In the 3rd phase, from 3-day pupa to adult, the connectives between the subesophageal and prothoracic ganglia, and between the pterothoracic and 3rd abdominal ganglia lengthen, and this increases the length of the CNS to 110% that of the 0-day pupa. Eventually the adult has a brain and 7 ganglia.