Lethal from embryonic to pupal stages, with 16% of homozygotes dying at the embryonic stage and 60% at the pupal stage. Most pupae stopped development in the early pupal period, displaying a misshapen puparium. The majority of mutants fail to shorten their body to form the characteristic shape of a prepupa and form long prepupae instead, also failing to evert anterior spiracles. Very rare mutant animals reach pharate adult stage - these show abnormal body proportions, and some are headless. Larval wing, haltere and eye-antennal imaginal discs are significantly smaller than wild type.
NAT1ex1 mutants frequently have extra scutellar bristles on the scutellum.
In contrast to wild type where the larval salivary gland degenerates early in the pupal stage, the gross structure of the salivary gland is still intact 24h after puparium formation.