Mutant tracheal terminal cells show a gas-filling defect at the stalk cell to terminal cell connection - most gaps are present in heterozygous stalk cell tubes adjacent to Vha26^okg-696 mutant cell clones. The defects are 100% penetrant with late onset (third larval instar). The stalk cell-terminal cell interface is also affected: 24% of Vha26^okg-696 cells exhibit stalk cells aberrantly forming two or more connections to a neighbouring terminal cell, and 9% of Vha26^okg-696 cells show a more severe defect in which long, branched autocellular, seamed tubes extend well beyond the terminal cell nucleus.

Vha26^okg-696 dorsal trunk clones are not fully integrated into the epithelium - cells are oval (not hexagonal) in shape. Vha26^okg-696 stalk cell clones have abnormal autocellular and intercellular junctions - these cells are detached from the epithelium or contribute a very short segment of autocellular tube.

Tubulogenesis in Vha26^okg-696 embryos is intact - ie. tube architecture only becomes disrupted over time as the the tracheal system increases in size.

oak-gall⁶⁹⁶ mutants exhibit thick and severely pruned terminal cells. There is defective intercalation/auto-cellular tube formation along with an auto-/sub-cellular tube gas-filling defect. Dorsal trunk cells are rounded and contribute minimally to multicellular lumen.