Quantità di adulti di Chirothrips manicatus Haliday (Thysanoptera Terebrantia) valutata su pannocchie di Arundo pliniana Turra (Gramineae) in Basilicata

Abstract

AMOUNT OF CHIROTHRIPS MANICATUS HALIDAY ADULTS (THYSANOPTERA TEREBRANTIA) EVALUATED ON COBS

OF ARUNDO PLINIANA TURRA (GRAMINEAE) IN BASILICATA

Number of adult thrips on A. pliniana cobs was monitored in 3 localities of Matera province (Southern Italy). Samples of cobs were collected every 15 days from mid-July to early January in each locality. A supplementary sample was collected in a single locality at mid-March. All samples included 90 cobs assembled from 3 separate groups of plants; in the laboratory, they were kept for drying in open basins. Adult thrips were daily collected from each sample as long as they left cobs, until their number did become lower than 15 for both sexes.

A very different amount of C. manicatus males and females was obtained throughout, and presence of other species of thrips was always found very low. Females of C. manicatus predominated from July to September. Male outbreaks occurred in October-November, when up to 18 thousands of males were obtained from a single sample. In December-January, females turned to be predominant, and no male was found in the supplementary sample of mid-March.

In author’s opinion, the arrhenotokous parthenogenetic reproduction of unmated females causes the autumnal outbreaks of C. manicatus males. Then, the latter trend to disperse in the environment, whereas most females stay on dead cobs for overwintering.

Key words: sex ratio, male outbreaks, overwintering.

È stata quantificata la presenza di adulti del terebrante Chirothrips manicatus Haliday sulle pannocchie della graminacea Arundo pliniana Turra in tre zone della provincia di Matera. I dati sono stati ottenuti da campioni di 90 pannocchie, prelevati in ciascuna zona ogni 15 giorni circa, da metà-luglio a metà-gennaio. Inoltre, è stato prelevato un campione supplementare a metà-marzo.

I risultati mostrano che le pannocchie di A. pliniana sono sede di una massiccia proliferazione di maschi di C. manicatus in ottobre-novembre. Secondo l’autore, questa sovrabbondanza di maschi può essere dovuta alla riproduzione per partenogenesi arrenotoca di femmine rimaste in maggioranza vergini a causa della scarsità di maschi nel precedente periodo estivo. All’inizio dell’inverno, le pannocchie sono popolate da una predominanza di femmine, probabilmente perché queste restano a svernare sulle pannocchie stesse, mentre i maschi si disperdono nell’ambiente. L’esame del campione prelevato a metà-marzo sembra confermare questa differente tendenza nei due sessi.

Parole chiave: sex ratio, eccedenza di maschi, svernamento.