Variation in Herbivory-induced Volatiles Among Cucumber (Cucumis sativus L.) Varieties has Consequences for the Attraction of Carnivorous Natural Enemies

In response to herbivory by arthropods, plants emit herbivory-induced volatiles that attract carnivorous enemies of the inducing herbivores. Here, we compared the attractiveness of eight cucumber varieties (Cucumis sativus L.) to Phytoseiulus persimilis predatory mites after infestation of the plants with herbivorous spider mites (Tetranychus urticae) under greenhouse conditions. Attractiveness differed considerably, with the most attractive variety attracting twice as many predators as the least attractive variety. Chemical analysis of the volatiles released by the infested plants revealed significant differences among varieties, both in quantity and quality of the emitted blends. Comparison of the attractiveness of the varieties with the amounts of volatiles emitted indicated that the quality (composition) of the blend is more important for attraction than the amount of volatiles emitted. The amount of (E)-β-ocimene, (E,E)-TMTT, and two other, yet unidentified compounds correlated positively with the attraction of predatory mites. Quantities of four compounds negatively correlated with carnivore attraction, among them methyl salicylate, which is known to attract the predatory mite P. persimilis. The emission of methyl salicylate correlated with an unknown compound that had a negative correlation with carnivore attraction and hence could be masking the attractiveness of methyl salicylate. The results imply that the foraging success of natural enemies of pests can be enhanced by breeding for crop varieties that release specific volatiles

NONLINEAR-REGRESSION METHODS FOR MODELING OF HETEROSCEDASTIC RETENTION DATA IN REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

New models have been developed that accurately describe the response surfaces of capacity factors that are a function of changes in the pH and the fraction of organic modifier in reversed-phase high-performance liquid chromatography (RP-HPLC). The purpose of this article is to illustrate one of the problems of nonlinear modeling of capacity factors; it is an extension of the articles on this nonlinear modeling in RP-HPLC that have appeared during the last three years. The main subject of this paper is a description of the methods that can be used in building correct models for the capacity factor as a function of both pH and modifier content of the mobile phase. The heterogeneity of the variance across all capacity factors causes the ordinary nonlinear least squares method to be less appropriate for regression. Two methods are described that take account of the effect of the heterogenic error structure of capacity factors in the modeling procedure. These two methods are then compared with the standard nonlinear modeling procedure

MULTICRITERIA DECISION-MAKING

Interest is growing in multicriteria decision making (MCDM) techniques and a large number of these techniques are now available. The purpose of this tutorial is to give a theoretical description of some of the MCDM techniques. Besides this we will give an overview of the differences and similarities of the techniques discussed. We have tried to select those techniques that are most frequently described in recent publications on analytical chemical and pharmaceutical subjects and, more important, that give a good survey of the diversity of techniques. We describe five different MCDM methods: Pareto optimality, desirability functions, overlay plots, utility functions and PROMETHEE. These techniques are compared to each other by applying them to a decision making problem in tablet manufacturin