Appunti di storia naturale su uno Ptilide partenogenetico: Ptinella mekura Kubota (Coleoptera)

Abstract

SOME REMARKS OF NATURAL HISTORY ON A PARTHENOGENETIC PTILIID,

PTINELLA MEKURA KUBOTA (COLEOPTERA)

Many tens of Ptinella mekura specimens were collected in a garden in Southern Italy, where they mainly occurred under man-made accumulations of grass and pine needles on coniferous humus; they sustained laboratory conditions very well and led to several generations in single vessels, throughout many weeks or months, and even for more than one year. Only wingless virgin females were collected in the field, and also the individuals born in laboratory were so.

Females possess a very large oviduct, where they mature a single large egg at a time. Eggs exhibit a predetermined ecclosion line and a characteristic frame to adhere at substratum. Egg development is 8-10 days long.

Fecundity was regarded as the number of eggs deposited by single females within 15 days after the installation of a rearing; it was evaluated by 4 series of rearings (6 rearings per series), respectively starting from 1, 2, 5 and 10 females collected in the field. 1 egg per day was recognized as the maximum value of fecundity.

The larval development is 15 days long and includes 2 instars. The number of the larval instars was evaluated on a statistic basis, by considering together the width of the head capsule and the length of the urogomphi in 25 specimens of larvae at random.

Larvae pupate after they have built a spherical chamber by soil particles. The pupal development is 5 days long. Freshly emerged adults are able to ovodeposit after 10 days.

Because literature does not report the presence of males in the collections from the whole world (Japan, Europe and USA), Ptinella mekura can be regarded as “obligatory and constantly parthenogenetic species”, according to the terminology of RETNAKARAN & PERCY (1985), in spite of the morphological constancy of its spermatheca.

Key words: Coleoptera, Ptiliidae, Ptinella mekura, rearing, parthenogenesis.

Numerose informazioni sul comportamento e sul ciclo vitale di Ptinella mekura Kubota sono state raccolte sfruttando le risorse di un giardino ricco di questa specie e installando numerosi allevamenti, di cui alcuni mantenuti per più di un anno.

Sono stati studiati gli organi interni, sono state ottenute le uova, è stato seguito lo sviluppo delle larve, è stata osservata la costruzione della cella pupale, è stata calcolata la fecondità massima delle singole femmine, è stata verificata per via diretta la capacità di riproduzione partenogenetica della specie.

Considerando i dati delle collezioni, Ptinella mekura viene giudicata quale specie completamente e costantemente partenogenetica.

Parole chiave: Coleoptera, Ptiliidae, Ptinella mekura, allevamento, partenogenesi.