Heat induced expression of EcR^B2.hs (using a single heat shock for 45 minutes at 37^oC) results in more than 50% lethality if the heat shock is started between 5 hours before puparium formation to 0.5 hours after puparium formation.

EcR^M554fs/EcR^V559fs larvae rescued through the moult to the third instar by repeated heat shocks (resulting in expression of EcR^B2.hs) show normal anterior progression of retinal differentiation in the eye discs. Discs are seen in which the furrow has traversed the entire eye field, reaching the antennal boundary (this represents a late stage of eye disc development that is normally only reached following pupariation).

EcR^M554fs/EcR^V559fs animals which have been rescued to the first larval instar stage by expression of EcR^B2.hs during embryogenesis have normal appearance and movement until the end of the first instar stage. If no further heat pulses are given, they arrest as first instar larvae. The arrested larvae survive for 1-2 days. Most rescued larvae arrest with both first and second instar mouth parts and posterior spiracles. Arrested larvae also appear to retain the first instar cuticle as well as the newly formed second instar cuticle.

EcR^M554fs/EcR^V559fs animals which have been rescued to the second larval instar stage by expression of EcR^B2.hs during embryogenesis and the first larval instar stage have normal appearance and movement until the end of the second instar stage. If no further heat pulses are given, they arrest as second instar larvae. Most rescued larvae arrest with duplicated larval cuticle and both second and third instar mouth hooks and posterior spiracles. The arrested larvae survive for 1-2 days.

EcR^M554fs/EcR^V559fs animals which have been rescued to the third larval instar stage by expression of EcR^B2.hs during embryogenesis, first and second larval instar stages appear normal at the beginning of the third instar stage. Progression through the third instar stage is significantly delayed. The mutant larvae generally stop feeding and begin wandering 48-72 hours following the second to third instar moult (wild-type larvae stop feeding and begin wandering 24-36 hours after the previous moult). Most mutant wandering larvae are able to clear their gut of food (as occurs in wild type). Most mutant larvae become stationary within 24-36 hours after beginning wandering (this occurs 12-24 hours after initiation of wandering in wild-type larvae) but retain their larval morphology without outward signs of pupariation. The mutant larvae can initially resume crawling and mouthpart movements if stimulated with a needle ("stage 1b"). Subsequent phenotypes are not seen in wild-type larvae. The larvae become incapable of resuming mouthpart movement or locomotion when stimulated with a needle ("stage 2"). This stage can be divided into three parts. In "stage 2a" the mutant larvae wriggle the posterior portion of the body, although the anterior tip of the larva appears to be fixed to the side of the culture vial. In "stage 2b" the mutant larvae have ceased wriggling but will resume wriggling if stimulated by a needle. At this stage, brown spots that may indicate necrosis begin to appear on the cuticle of some larvae. "Stage 2c" mutant larvae do not resume posterior wriggling when stimulated by a needle. Most stage 2c larvae have brown areas present on the cuticle. Throughout stage 2, mutant larvae continue to show dorsal medial abdominal contraction (ie. heart pumping), which is no longer detectable in wild-type larvae between 1-7 hours after pupariation. "Stage 3" mutants lack any response to stimulation and have ceased dorsal medial abdominal contraction. Necrotic patches of tissue continue to accumulate and the larvae ultimately deteriorate. Imaginal discs from mid-third instar EcR^M554fs/EcR^V559fs animals which have been rescued to the third larval instar stage by expression of EcR^B2.hs during embryogenesis, first and second larval instar stages are indistinguishable from wild type. Leg discs initiate elongation in the mutant larvae but arrest shortly afterwards. The gastric caeca from mid-third instar mutant larvae appears normal and shortening of the gastric caeca is initiated. However, gastric caeca shortening is not completed, and appears to arrest at a stage comparable to 2 hours after pupariation in wild type. The larval salivary glands persist in mutants. The midgut imaginal cells appear normal in mid-third instar mutant larvae, but do not proliferate.