obst-E^KO homozygotes and obst-E^KO/obst-E^Del transheterozygotes are first instar larval lethal. No apparent morphological defects are observed in the cuticle of the obst-E^KO or obst-E^KO/obst-E^Del mutant first instar larvae, but the hindgut (although morphologically normal during embryogenesis) protrudes out of the anus in these larvae - likely constituting the primary reason for their lethality.

obst-E^CPTI100067/obst-E^KO as well as obst-E^CPTI002377/obst-E^KO transheterozygous pupae are longer and thinner than wild-type and have significantly higher axis ratio (AR, length/width), despite having normal appearance and AR in the larval stages. The AR of obst-E^KO heterozygous pupae is comparable to controls.

Scer\GAL4^Act5C.PU-driven expression of obst-E^Scer\UAS.b rescues the lethality of obst-E^KO/obst-E^Del transheterozygotes but the 'rescue' pupae show body shape defects (are thinner and longer than controls) due to failed shape change and contraction upon dehydration of the larval cuticle during metamorphosis. The prepupae show normal internalization of the anterior segments but the anterior spiracles fail to evert and remain encapsulated within the puparium. In contrast to wild-type, no ridges are observed on the inner surface of third instar larval cuticle of the mutant animals and the surface appears essentially flat with the exception of a narrow lateral region where some of the ridging is partially preserved. Although the general three-layer organization of the cuticle is maintained, unlike the lamellae in wild-type, the lamellae in the procuticle layer of the mutants are flat, of constant thickness and tend to contain unidirectional arcs. No apparent morphological aberration are observed in the cuticle of first or second instar larvae.