STUDI SULLE LARVE DEI COLEOTTERI DITISCIDI VII

Abstract

SOME REMARKS ON THE EVOLUTIONISTIC MEANING OF THE BEHAVIOUR OF THE MANDIBULAR

CHARACTERS IN THE LARVAE OF SOME SPECIES OF THE SUBF. Dytiscinae

The purpose of this paper is to provide data for the inspection of an hypothesis that the author sketched out in a previous paper (DE MARZO, 1976b) - that the patterns of mandibula of the larvae of the subf. Dytiscinae have their morphogenetic origin in the mandibular pattern of the larva of Melanodytes pustulatus (subf. Colymbetinae). The mandibulae of 8 species (5 genera, 5 tribes) of the subf. Dytiscinae are described in detail and the data collected in this way are analized. Five patterns of mandibula are singled - one pattern for each genus taken into consideration - whose characteristics

appear such to support the initial hypothesis.
The five patterns, in fact, look to have a common ongm, mainly because they ali

show a pubescence - on the ventral lip of the fare orifice of the mandibular groove - which is interpreted as inherited from an unique pattern, having that pubescence. In the opinion of the author, this precursory pattern might be the pattern of Melanodytes pustulatus.

Viene vagliata l'ipotesi di lavoro, avanzata in un precedente studio. secondo la quale i modelli di mandibola delle larve della subf. Dytiscinae deriverebbero dal modello osservato nella larva di Melanodytes pustulatus Rossi (subf. Colymbetinae). A tale scopo, vengono dettagliatamente esaminate ed analizzate le caratteristiche delle mandibole delle larve di otto specie della subf. Dytiscinae. Vengono così individuati cinque modelli di mandibola, uno per ciascuno dei generi presi in considerazione, le cui caratteristiche appaiono tali da sostenere l'ipotesi di lavoro suddetta.