Hemizygous larvae are smaller than wild-type larvae from the late second instar onwards, with the defect becoming more striking during the third instar. The moult from second to third instar is delayed by approximately 12 hours in mutant animals, and the third instar is extended by two days compared to controls. Mutant animals fail to undergo metamorphosis, dying at the end of the third larval instar or shortly after, forming abnormal elongated pupae.

Whole body triglyceride levels are significantly decreased in mutant third instar larvae compared to wild type.

Fat body cells are smaller than in controls in mutant third instar and wandering larvae. However, homozygous clones of cells in the larval fat body are equal in size to the surrounding heterozygous cells and starvation has no differential effect on cell size within the mutant clones.

Homozygous third instar larvae have a pronounced brush border in the midgut epithelia (as occurs in wild type), but the mutant midgut epithelial cells show marked vacuolation. The midgut musculature has a ragged appearance in late mutant third instar larvae, with both the circular and longitudinal muscles being smaller than in controls. The thickness of the hindgut muscle fibres is also reduced in the mutant larvae compared to wild type.

Mutant third instar larvae transferred to dyed food show a similar amount of dyed food in their gut as control larvae after 24 hours feeding. However, the mutant larvae show a defect in gut clearance, with significant amounts of dyed food remaining in their guts even 24 hours after removal of the dyed food (most wild-type larvae clear the dyed food from their guts within 10 hours).

Peristaltic contractions are not seen in freshly dissected mutant third larval instar midguts, in contrast to the spontaneous muscle contraction seen in the majority of wild-type guts.