Nuovi dati anatomici e citologici sul presunto simbiosoma dei Coleotteri Meliridi

Abstract

NEW ANATOMICAL AND HISTOLOGICAL DATA ON THE SUPPOSED SYMBIOSOME OF THE MELYRIDS (COLEOPTERA)

Observation by light- and electron microscopy was carried out to discuss the biological signifi- cance of the mulberry-shaped organs of the female Melyrids, here referred as “Holmgren’s organ”. This was differently regarded by authors, either as group of oenocytes or as symbiotic transmission device.

The new data on this organ show its presence in both adult females and males of Henicopus, Dasytes and Psilothrix; its absence in Divales and Danacaea; its presence in last-instar larvae of Psilothrix viridicoerulea (Geoffr.); its sex dimorphism in adult; its lack of sex dimorphism in larvae; its regression during the reproductive season in both males and females; its lack of cytopla- smatic structure which can be referred to microorganisms.

A review from the literature leads the author to regard the term “oenocyte” as very poor of cytological significance if not referred to single species. So, the Holmgren’s oenocytes are defined as follows: large size, globose shape, large nuclei, lacking in cell polarity, located without metameric order, connected with the gut in both females and larvae, free in the hemocoel in males, trending to regress in both adult females and males possibly in correlation with the gonad development.

Key words: Melyridae, symbiosis, oenocytes, fine structure.

Il classico organo femminile di Dasytes niger, qui indicato come “organo di Holmgren”, viene rivisto in merito al suo significato funzionale dopo l’acquisizione di nuovi dati sulla sua presenza negli adulti dei due sessi di altre specie di Meliridi e nelle larve di Psilothrix viridicoerulea. Lo studio ultrastrutturale conferma la tesi originale dello scopritore, riguardo alla natura ghiandolare dell’organo e, data la mancanza di strutture riferibili a microrganismi, esclude la tesi di un suo ruolo nell’endosimbiosi.

Viene fatta una rassegna bibliografica sulle caratteristiche dell’enocita, dalla quale risultano attribuite a questo termine un gran numero di caratteristiche diverse e variabili che lo rendono povero di significato senza l’indicazione della specie considerata.

Parole chiave: Melyridae, simbiosi, enociti, ultrastruttura.