Both, investigations and evaluation of plant protection effects on beneficial arthropods in fields succeed only by using bioindicators which respond to different environmental variables or changes (stressors) with measurable state reactions. In field crops a range of indicators is suitable, single species as well as whole taxonomic groups and so-called guilds (predatory mites, specialized aphid predators, epigeous arthropods, predatory flies, aphid parasitoids and parasites of rape pests). Population responses in quantity (density, motoric activity) and quality (species composition, dominance structure, diversity, phenotypical variability, biological capacity) have to be considered. Unfortunately, the methods available for all interesting indications have their limitations and are different suitable in several field crops. Field studies should be realized as direct comparisons of plant protection types at the same site considering short-term and sustainable effects. A description of status of beneficial communities at different sites does not be a sufficient base for the incidences of an ecological impact of plant protection. For investigation of sustainable effects the data samplings have to carry out over a year as minimum. Because clear outlines of ecological values for agro-ecosystems do not exist the interpretation of findings including different groups of beneficial arthropods is difficult. Considering our view on tritrophic systems with interspecific and intraspecific interactions a combined approach for evaluation should be established. An important aim is to standardize methodical conceptions of field studies and to develop interpretation helps.