A long-term study on the population dynamics of the grape leafhopper (Empoasca vitis) and antagonistic mymarid species

The population dynamics of the grape leaf-hopper (Empoasca vitis) and its egg parasitoids (Mymaridae) were studied at five representative sites in the Franconian wine-growing region from 1998 to 2001. In contrast to other German wine-growing areas, only one generation of grape leafhoppers per season was observed. In general, irrespective of the application of insecticides, the peak density of the first generation was much lower than that of immigrating grape leafhoppers. As the observed mymarid:leafhopper ratios (1:0.8-1:4.8) of the first generation were extremely high, egg parasitoids might be effectively controlling the grape leafhopper in Franconian vineyards. Slightly elevated leafhopper densities at the end of the growing season were caused by migrating sister species. Intervention thresholds were rarely reached; however, stress symptoms as discoloured intercostal leaf areas or rolled leaf edges were widespread. Over the whole study period three mymarid species occurred at all monitoring sites: Anagrus atomus, Stethynium triclavatum and a species, not previously reported in the German wine-growing region, Anagrus avalae. The dominance relationships of these species were site-specific, differing more strongly between than within sites; however, differences could not be related to the kind of management or natural surrounding of the vineyards. A hatching experiment confirmed the biological significance of A. avalae as an effective antagonist.