EcR¹³⁹/EcR^M554fs third instar larvae have the same number of Burs-immunoreactive CCAP neurons as wild-type controls. At 24-48 hours after puparium formation there are more Burs-immunoreactive abdominal CCAP neurons than in +/EcR^M554fs controls and some CCAP neurons retain larval features such as small soma size and larva-like projections.

EcR¹³⁹/EcR^M554fs mutants show a range of lethal phases and a loss of coordination of larval wandering and pupariation behaviour. Almost 70% of EcR¹³⁹/EcR^M554fs mutants survive to the third instar larval stage and these mutant larvae show abnormal larval wandering behaviour. Unlike wild-type larvae, EcR¹³⁹/EcR^M554fs third instar larvae continue feeding and often fail to wander in search of a suitable pupariation site, resulting in their pupariation on food. The mutants seem to physically resist pupariation and their aberrant movement causes the formation of a misshapen puparium. Over 60% of EcR¹³⁹/EcR^M554fs mutants survive to pupal stage P5 and most progress through head eversion, eye development, and leg and wing extension. Dessication and necrosis of the pupa is frequently evident at this stage. Additionally, puparium formation is defective; the puparium fails to shorten and tan normally, and the cuticle fails to harden to wild-type levels. Around 15% of EcR¹³⁹/EcR^M554fs mutants survive to pharate adult stage P15, but these animals fail to eclose and degenerate within the pupal case. EcR¹³⁹/EcR^M554fs pharate adults have abnormally short legs, with rounded tarsal segments and kinked femurs.

60% of EcR¹³⁹/EcR^M554fs mutants survive to the second larval instar stage, 40% survive to the third instar and pupal stage, but all are dead by the adult stage.