The association of Tarsonemus mites (Acari: Heterostigmata) with different apple developmental stages and apple core rot diseases

Abstract

Information on the role of mites in the genus Tarsonemus Canestrini and Fanzago, 1876 in the epidemiology of apple core rots (wet and dry) is limited. The aims of this study were to (1) assess the effect of different apple developmental stages (buds, blossoms, 4-cm diameter fruit, mature fruit and mummies) on the relative abundance of Tasonemus mites, (2) determine if there is a tendency of Tarsonemus mites to be associated with wet core rot (WCR) and dry core rot (DCR) apples, and (3) evaluate the suitability of three core-rot-associated fungal genera as food sources for the mites. Investigations into four orchards, two core-rot-susceptible (Red Delicious) and two-core-rot resistant (Granny Smith), revealed that Tarsonemus mites were the dominant mite genus in all the apple developmental stages in all orchards. The Tarsonemus mites had the highest incidence in mature fruits and mummies in all the orchards. In the cores of healthy and DCR Red Delicious fruits, Tarsonemus mites had a high occurrence of 56% and 84%, respectively. In these fruits, a significant association was found between DCR and the presence of mites in the core. In contrast, in Granny Smith fruits, mites were restricted to the calyx tubes, and only a calyx tube decay symptom was identified. The Tarsonemus mites were fungivorous and reproduced on cultures of a Cladosporium sp. Cultures of Alternaria sp. and Penicillium sp. were unsuitable for mite reproduction, even though the mites did ingest a red fluorescently labeled Alternaria sp. culture. The survival and reproduction of mites on fungal cultures were better at 30°C than at 25°C.