Grape downy mildew spread and mite seasonal abundance in vineyards: effects on Tydeus caudatus and its predators |
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| Institution: | 1. Applied Molecular Solutions Research Group, Environmental and Animal Sciences, Unitec Institute of Technology, Private Bag 92025, Victoria Street West, Auckland 1142, New Zealand;2. Bio-Protection Research Centre, PO Box 85084, Lincoln University, Lincoln 7647, New Zealand;3. Department of Entomology, Washington State University, Pullman, WA 99164-6382, USA;1. Critical Care Medicine Research Group, Department of Intensive Care, Tampere University Hospital, Tampere, Finland;2. Department of Surgical Sciences, Division of Anesthesiology and Intensive Care, Uppsala University, Uppsala, Sweden;3. Faculty of Social Sciences, University of Tampere, Tampere, Finland;4. The Immunopharmacology Research Group, Faculty of Medicine and Life Sciences, University of Tampere, Tampere University Hospital, Tampere, Finland;5. Department of Neurology, University of Tampere and Tampere University Hospital, Tampere, Finland |
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| Abstract: | Tydeus caudatus (Acari: Tydeidae) can prey upon grape eriophyoid mites but little is known about its alternative foods. Observations carried out during 1999–2003 in a commercial vineyard located in northeastern Italy showed that densities of T. caudatus were often correlated to downy mildew spread on the vegetation. Densities of T. caudatus increased in late summer when downy mildew symptoms occurred on a high number of leaves. The predatory mite Paraseiulus talbii (Acari: Phytoseiidae) increased in late season following the increase of tydeids. On several sampling dates, T. caudatus populations were significantly higher on leaves with downy mildew symptoms than on leaves without symptoms. Tydeid densities were often positively correlated to the extent of leaf surface showing symptoms. These relationships were sometimes found regarding P. talbii. In two experimental vineyards colonised by T. caudatus, untreated plots or plots treated with different fungicides to control downy mildew were monitored during 2002. Downy mildew infections rapidly spread in the control plots while they were effectively controlled on fungicide-treated plots. In both vineyards, T. caudatus densities reached significantly higher densities in the control than on fungicide-treated plots. A field study showed that most of these fungicides did not reduce tydeid populations when downy mildew was virtually absent. Isoelectric-focusing electrophoresis (IEF) was used to detect downy mildew in mites. Glucose phosphate isomerase (GPI) was selected from among different enzymes. A high proportion of T. caudatus females, collected from infected leaves, and analysed under IEF showed a GPI isozyme allele corresponding to the downy mildew isozyme in addition to the tydeid intrinsic alleles. This phenomenon was also observed for P. talbii but with a lower incidence. All T. caudatus females confined on symptomatic leaves became positive by IEF after few hours but the same did not occur with P. talbii. A high proportion of P. talbii females became positive after preying on tydeids collected from symptomatic leaves or reared on pollen and then confined on symptomatic leaves. |
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