STUDI SULLE LARVE DEI COLEOTTERI DITISCIDI VIII

Abstract

MORPHOLOGY OF THE THREE LARV AL INST ARS OF O r e o d y t e s r i v a l i s GYLL. AND H y p h y d r u s aubei GANGLB. AND SOME REMARKS ON THE BEHAVIOUR OF THE ESOSKELETRIC CHARACTERS IN THE LARVAL FORMS OF THE SUBF. Hydroporinae

The three larval instars of two species of the subf. Hydroporinae are described and compared each other. These species, Hyphydrus aubei and Oreodytes rivalis, belong respec- tively to the I and to the XX - and last - european genus of the Subfamily; they are, besides, largely different under the point of view of the larva! morphology, because they show a very different shape of the «frontal horn», which is a peculiar structure of the Hydroporinae larvae.

Such a choise allows to identify the characters whose behaviour shows a tendency to be variable, or constant, in the ambit of the Subfamily.

In the last part of the paper the author analizes some characters of the two species, taking into consideration data regarding other species of the same and other subfamilies. Particularly he points out the behaviours which may reasonably regarded as primitive ones, i.e., which may attributed to the ancestral larva! form, from which the present larva! forms of the subf. Hydroporinae rise, or may attributed to a some more primitive larva! form, from which the subff. Hydroporinae, Laccophilinae and Colymbetinae rise together.

The author bases the discussion on the more commonly accepted phylogenetic theory on the origin of the subfamilies of the Dytiscidae (GUIGNOT, 1931-33, page 889). In the opinion of the author, the data exposed in the present paper support that theory.

Viene fatta la morfologia comparata dei tre stadi !arvali di due specie della subf. Hydroporinae, molto distanti fra loro dal punto di vista della Sistematica immaginale e molto diverse per quanto concerne le caratteri- stiche più appariscenti della loro morfologia !arvale. Si è ritenuto di potere, con tale scelta, individuare più agevolmente i caratteri che tendono ad un compor- tamento variabile e quelli che tendono ad una staticità di comportamento nel- l'ambito della Sottofamiglia. Sulla scorta dei dati cosl ottenuti, e tenendo presenti anche dati ricavati dalla bibliografia, vengono avanzate ipotesi sul significato filogenetico del comportamento di alcuni caratteri nelle subfi. Hydroporinae, Laccophilinae e Colymbetinae.