At stage 15, the dorsal trunk lumen in knk² mutants remains constricted at branch fusions and the tube between fusion junctions becomes excessively overgrown compared to wild-type, exhibiting a cystic-like appearance. Stage 16 knk² mutant embryos display irregular tracheal tube shapes, but do not exhibit defects in branch patterning, compared with wild-type embryos. During stage 16, the knk² mutant dorsal tube becomes extensively elongated compared with the wild-type trunk. The lumen of the narrower multicellular ganglionic branches is discontinuous in knk² mutants at the border of the ventral nerve cord. Lumen expansion from stage 14 to 15 does not involve cell division and relies on coordinated growth of the apical cell surfaces. knk²/knk¹ larvae exhibit a dilated cuticle with a strongly deformed and melanised head skeleton.

Homozygous embryos have defects in the head skeleton and denticle belts.