Monitoring deformities of Chironomus riparius Meigen, 1804 (Diptera, Chironomidae) larvae from first to fourth instar: a potential tool for investigating their origin

Abstract

We monitored changes in the morphology of the mentum and mandibles of Chironomus riparius MEIGEN, 1804 larvae over the entire larval development process. Larvae were reared in isolation in individual tubes containing clean water. Head capsules of each instar were collected just after moulting and mounted on microscope slides. Study of the head capsules showed that deformities may arise in any of the larval instars, and may be maintained or partially or completely repaired in subsequent moulting processes. Moulting from the first to the second instar presented special characteristics: notably, the common mandible deformity missing tooth with gap was never transferred to second-instar larvae, while other types of deformity were preserved during the first- to second-instar transition. Interestingly, the missing tooth with gap deformity often occurs in several larvae from a single egg-mass. These results thus provide support for the hypothesis that repeated deformities in first-instar larvae from the same egg mass are not due to the same causes as other deformity types. In the light of the present and previous results, we discuss what physiological mechanisms may account for the origin of deformities.