Organization of the cuticle of an aquatic fly larva

The aquatic, apneustic larva of the midge, Chironomus riparius, has a very thin (up to 5 micrometers), readily deformable, post-cephalic cuticle. The ultrastructure of this cuticle from newly moulted and older final instar animals, and exuvia shed at pupation, has been examined using routine methods and also after the extraction of proteins with formamide and acetic acid. From the results described, and using established criteria, it is inferred that an exocuticle is present and represents about 25% of the thickness of the mature procuticle, the remainder being endocuticle. Therefore, it would seem that this exceptionally delicate cuticle conforms to the conventional plan of tanned or sclerotized solid cuticles, unlike those reported in the larvae of cyclorrhaphous dipterans such as blowflies or other soft-bodied insects. This is the first account, using experimental techniques, of the fine structure of sectioned cuticle from nematocerous dipteran larvae. It also indicates the value of the exuvium as a source of information about cuticle structure.