In the larval respiratory system, B5- lacZ expression is observed in imaginal tracheoblasts, which are easily identified by their small size compared to neighboring larval tracheal cells and close association with the larval tracheal network. Two types of clusters are seen, one round and one elongate. Round clusters are found in thoracic segments only, and are situated next to the dorsal longitudinal trunk. Elongate clusters are stretched along the visceral and spiracular branches, which emanate from the transverse connectives and are segmentally repeated down the length of the larval trunk. Larval glands that express B5- lacZ include the imaginal ring of the salivary gland, the ring gland , the lymph gland and pericardial cells flanking the length of the aorta.
Alimentary expression includes the foregut and hindgut imaginal rings, and midgut imaginal islands.
In the male, B5- lacZ is found in apically associated cells of the testis. These cells correspond to the mitotically dividing gonial cells and remain positive in the adult male, where expression is concentrated at the anterior tip of the testis. Drosophila metamorphosis is characterized by diverse developmental phenomena, including cellular proliferation, tissue remodeling, cell migration, and programmed cell death. Additional pulses of ecdysone further coordinate these processes during the prepupal and pupal phases of metamorphosis. Larval tissues such as the gut, salivary glands, and larval-specific muscles undergo programmed cell death and subsequent histolysis.