Induces the early late puff 78C which triggers puparium formation and development. Isoform A is expressed only in mid-pupal stages, while isoform B is maximally expressed in newly formed prepupae and immediately following isoform A in mid-pupae. Isoform A and isoform B require ecdysone for activity. Isoform B also requires ecdysone-induced proteins for maximal expression. Belongs to the nuclear hormone receptor family. NR1 subfamily.