Transheterozygous Mbs³/Mbs^P2r31 animals grow slowly. They become wandering third instar larvae 6 to 7 days after egg laying (AEL) as compared with the normal 5 days AEL. After starting to wander, the mutant larvae are semi-paralysed, and survive for several days without forming puparium. In such mutant larvae, imaginal discs continue to grow and develop to a slightly larger size than that of wild-type discs. These mutant imaginal discs, compared with wild-type, are disorganised and multi-layered. Furthermore, adjacent imaginal discs are frequently fused to each other, suggesting a tumorous growth of imaginal cells.

In the wild-type wing imaginal disc, marked cells are observed within a straight stripe along the anterior-posterior boundary. In contrast, the anterior-posterior boundary in Mbs³/Mbs^P2r31 mutant discs, as visualised by marked cell clones, appears diffuse, not well defined.

Lethal phase of Mbs^P2r31 mutants spans from the third larval instar to the early pupal stage. Mbs^P2r31/Df(3L)th117 animals survive to the third larval instar.