Research and management oriented sampling plans for vine inhabitingScaphoideus titanus grape leafhopper nymphs
Abstract: This paper summarizes the methodology used for describing the spatial distribution ofthe grape leafhopper Scaphoideus titanus in a vineyard located in Southern Switzerland andpresents sampling plans for research and management purposes. The sampling techniqueconsisted of repeated visual counts of S. titanus nymphs. In general, a vineyard is a highlystructured environment whose influence on spatial distributions is studied by analyses of varianceand 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 trunkshoot leaves and the mean density of trunk shoot leaves. This allowed the translation of a criticaldensity for entering the vineyard in an adaptive management (AM) program into a criticalproportion. A sequential binomial sampling plan was developed to efficiently decide whether avineyard should be included into the AM program or not. Second, the spatial distribution in theentire vine plant canopy was analysed. Since there were significant differences between densitieson 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 positionwithin 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 thevineyard, shoot type and shoot levels. On the basis of this statistics, enumerative and sequentialsampling plans are proposed and implemented in the AM framework. The here presentedsampling techniques are advantageous over the previously used beating tray method and thesampling plans are useful for research and management purposes.