SEGNALAZIONE DI UN ACARO TETRANICHIDE DANNOSO AL CASTAGNO IN SICILIA

Abstract

Viene segnalata la presenza in Sicilia di Oligonychus bicolor (Banks), Acaro Tetranichide dannoso al Castagno e ad altre latifoglie, precedentemente noto solo per la Regione neartica.

Dopo la descrizione morfologica della specie, illustrata con disegni originali, sono indicate le sue piante ospiti e la distribuzione geografica; quindi viene descritta la sintomatologia delle alterazioni indotte dall'attività fitofaga dell'Acaro sulle foglie del Castagno e illustrato brevemente il suo comportamento bio-etologico nelle zone orientali della Sicilia.

A Tetranichid mite, Oligonychus bicolor (Banks), new to Italy has recently been found in Sicily on chestnut and oak. Here, in the eastern part of the island, this mite was found heavily infesting chestnut leaves, feeding on the upper surface.

Until this record the mite was known only in the nearthic region; in fact its distribution interests some areas of the United States, particularly on the east coast, and south-eastern Canada.

The adult female of O. bicolor measures, on an average 0,35 mm in length and the species may be recognized by some microscopic characteristic, both of female and male.

On chestnut leaves the mite lives along the midrib and lateral veins, where it determines evident discoloration of the infested areas due to its feeding activities. Here the mite secretes silken threads, under which it lives and the female lays the summer eggs which are well attached to the upper surface of the leaf. During the summer months there are various generations, so the leaf infestation is protracted throughout this whole season. The female lays ber winter eggs, starting from about the middle of September, on the twigs and small branches of the host. These eggs hatch from about the first week in May. Both the winter and summer eggs are very similar in form (union-shaped with rather long dorsal filament) and colour.

The infested leaves are not subjected to any deformation or to any appa· rent decrease in development, and it has not been observed if there is a premature leaf drop. So the damage consists principally in the discoloration of the infested areas of the leaves that, sometimes, is very evident. It is important to note that in some extreme cases single trees have been observed with all their leaves infested by the mite.