Ontogenesis, transfer and repair of mouthpart deformities during moulting in Chironomus riparius (Diptera, Chironomidae)

Ontogenesis, transfer and repair of larval chironomid deformities during mo ulting are described for the first time. Third instar Chironomus riparius l arvae from a contaminated stream were individually reared to fourth instar in the laboratory. Mentum and mandible deformities present in the third ins tar exuvial head capsule were then compared with deformities in the fourth instar larva. Instar IV larvae displayed higher deformation frequencies tha n instar III larvae. The majority of the deformities in instar III were ide ntically passed on during moulting. Partial and complete repair occurred to some extent, indicating that chironomid mouthpart deformation can be rever sible. The frequency of deformed instar III larvae gaining additional defor mities after moulting, was equal to the frequency of normal larvae with def ormities after moulting. This shows that the presence of deformities does n ot increase the susceptibility for the formation of new deformities. The ef fects of physical tooth damage on the formation of mouthpart deformities wa s also investigated, but no relationship was found between tooth breakage/a brasion and deformation. The difference in deformation frequency between in star III and IV larvae once again stresses the importance of separate scree ning of different instars for biomonitoring and toxicity testing purposes.