Research and management oriented sampling plans for vine inhabiting Scaphoideus titanus grape leafhopper nymphs

This paper summarizes the methodology used for describing the spatial distribution of the grape leafhopper Scaphoideus titanus in a vineyard located in Southern Switzerland and presents sampling plans for research and management purposes. The sampling technique consisted of repeated visual counts of S. titanus nymphs. In general, a vineyard is a highly structured environment whose influence on spatial distributions is studied by analyses of variance and quantified by regression models developed in a stratified and multi-stage sampling universe. First, a regression model was applied to the relationship between the proportion of infested trunk shoot leaves and the mean density of trunk shoot leaves. This allowed the translation of a critical density for entering the vineyard in an adaptive management (AM) program into a critical proportion. A sequential binomial sampling plan was developed to efficiently decide whether a vineyard should be included into the AM program or not. Second, the spatial distribution in the entire vine plant canopy was analysed. Since there were significant differences between densities on trunk shoots and productive shoots, two different sampling plans were designed. However, there were no significant differences between other strata (parts of the vineyard, leaf position within shoots), so that they were disregarded in sampling plan design. The mean crowding - mean regression model, with the intercept set to 0, indicated aggregated distributions at the vineyard, shoot type and shoot levels. On the basis of this statistics, enumerative and sequential sampling plans are proposed and implemented in the AM framework. The here presented sampling techniques are advantageous over the previously used beating tray method and the sampling plans are useful for research and management purposes.