dsb^ko mutants die before reaching pupal stage with almost 60% dying during second instar stage. The larvae are much smaller and thinner than controls: the decreased body size is noticeable as soon as 24hr after larval hatching and the difference grows more pronounced as the development progresses. dsb^ko larvae are more transparent, suggesting less fat accumulation and display feeding behavior defects and yeast paste avoidance. There are morphological abnormalities in the airways of first instar mutant larvae: the transverse angles formed at the junction between the dorsal trunk and the transverse connective branches are altered due to defective dorsal trunk elongation. The defective elongation becomes more obvious in older larvae when the dorsal trunk becomes stretched until finally the posterior spiracles get internalized into the body cavity, trunk breaks are also frequently observed. The gross morphology of filzkorper is unaffected in dsb^ko mutants and all mechanosensory hairs surrounding the opening of each spiracle are present but liquid clearance at, as well as water tightness of, the posterior spiracles is considerably impaired. The ultrastructure of the spiracles (shape of the spiracular plate, distribution and structure of the hairs, patterning of the openings) in dsb^ko mutants is indistinguishable from wild-type controls, although occasional electron dense clumps between more electron lucent zones in the procuticle. No signs of cell death in cells surrounding the spiracular lumen and the cuticle at the epidermis appear normal.