Expression of Spn4^4.1.Scer\UAS under the control of Scer\GAL4^dimm-929 (which drives expression in ~200 peptidergic CNS neurons and in the peritracheal Inka cells) results in a significant increase in both larval and pupal lethality. There are no apparent defects in either embryonic development or hatching. The first instar larvae exhibit no significant defects in either locomotion or feeding behavior; however, there is a block of developmental progress at a characteristic point in larval ecdysis for many Spn4^4.1.Scer\UAS inserts that results in larval death (the strongest effects are found with P{UASp-Spn4.1}283). Some Spn4^4.1.Scer\UAS larvae survive to pupation, wherein they are observed as partially collapsed within their pupal cases.

Lethality and molting defects are observed when Spn4^4.1.Scer\UAS is expressed using Scer\GAL4^how-24B to drive expression in muscles and other mesodermally derived tissues, nerves, and trachea, as well as a subset of cells in the CNS (with the larvae arresting development at the L1 to L2 ecdysis).

Larvae overexpressing Spn4^4.1.Scer\UAS under the control of Scer\GAL4^how-24B or Scer\GAL4^dimm-929 are able to proceed to the sclerotised double mouthhooks and double ventral plates stage normally but then remain trapped there for up to 24 hours (compared to the whole period lasting for about 1 hour in wild-type).