STUDI SULLE LARVE DEI COLEOTTERI DITISCIDI IV. Morfologia dei tre stadi larvali di Copelatus haemorroidalis F.

Abstract

È trattata la morfologia esterna dei tre stadi larvali di Copelatus haemorroidalis F. (Dytiscidae, Colymbetinae) con l'intento di studiare le variazioni che essa subisce nel corso dello sviluppo larvale e di paragonarla con quella delle specie precedentemente esaminate; viene considerato con particolare attenzione il comportamento della chetotassi delle larve neonate. Si mettono in evidenza, inoltre, i caratteri che, nell'ambito della subf. Colymbetinae, appaiono esclusivi di specie del genere Copelatus.

MORPHOLOGY OF THE THREE LARVAL INSTARS OF Copelatus haemorroidalis F.

The author relates about the characters that differentiate among them the three larval instars of Copelatus haemorroidalis F. This species has been taken into consideration because it belongs to the tribe Copelatini of the subf. Colymbetinae (in the preceding papers of the author some species of the tr. Agabini and tr. Colymbetini of the same Subfamily were examined).

The morphology of this species is furthermore compared with that of the previously treated species and, in comparison with this, it showes some peculiar characters mainly règarding the head appendages: antennae with two appendages at the apex of the third segment, third antennal segment with three setae, mandibules without mandibular canal, maxillae with big claw-like appendages (in addition to the galea). Within the species of subf. Colymbetinae that are treated in the papers of the consulted bibliografy none of these characters is present, except in other species of the same tribe.

Comparing the chetotaxy of the first instar larva of Copelatus with the chetotaxy of the previously treated first instar larvae, it is noticed that inter- or intraspecific variability may be found in the number of setae of determinate setae groups (setae of clypeal edge, dorsal face of prelabium, pronotum and femur); in different Genera it may be also noticed a little difference in the chetotaxy of thoracic sternites and pleurites and the presence or absence of the seta V2 in the abdominal VII and VIII segments. All the other setae of the fìrst instar larva are strictly constant and homologous in the since now examined species.