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Description / Table of Contents: Summary The effect of 5 herbicides widely used in agriculture (active ingredients: alachlor, chlorfenpropmethyl, desmetryne, phenmedipham, propachlor) were studied, mainly in the laboratory, by measuring the reduction of beneficial capacity of three entomophagous insects showing quite different behaviour. The egg parasiteTrichogramma cacoeciae March. reacted very strongly in laboratory tests as well as in the field under the influence of the herbicides. Contact toxicity tested on residues on glass plates caused a reduction of the degree of parasitization leading to total mortality of the population, in contaminated cages for some preparations. Part of this effect was caused by the zero formulation examined simultaneously. In the study of the contact toxicity of the spray deposit on single leaves as well as on whole plants the strong effect onTrichogramma by some of the preparations was shown. This direct toxic effect should be discerned from a repellent effect which was probably more important in the field. In addition to this direct contact effect of spray deposits also systemic application caused an effect after transportation of herbicides through the soil and the plant. This was clearly demonstrated by a reduction of the degree of parasitization in comparison to untreated controls. The herbicides studied do not seem to have any influence onChrysopa carnea Steph. larvae. No effect was visible, neither in tests of contact toxicity or contaminated sandy soil nor in choice experiments on a repellent action of the residue or after topical application of the preparations. — Also after peroral application through an artificial food chain no influence of the preparations could be demonstrated. Only the overdosage of one herbicide increased the mortality rate of the test larvae. The adults showed also no repellent reaction against the herbicides tested in choice experiments. The syrphidEpistrophe balteata DeG., however, reacted in a more sensitive manner on the influence of herbicides. Both, in contact experiments of toxicity as well as in choice experiments for a possible repellent effect an influence on the larval stages of the herbicides examined was shown. The peroral intake over an artificial food chain had no effect on the larvae after systemic application of the herbicide. If, however, the same herbicide was sprayed directly on the plant, an increase of larval nortality was observed. Adults of this syrphid showed also reactions on herbicide residues. Females during egg deposition avoided surfaces previously treated by the herbicide (phenmedipham). In tests on a possible ovicidal effect of herbicides on the eggs of all 3 entomophagous species only one herbicide (chlorfenpropmethyl) reduced the rate of egg-hatching of syrphids quite clearly. In summing up it can be said that damages as observed depend on the species as well as on the herbicide applied and the type of application. Losses of sensitive entomophagous species in the field might well be possible according to the results obtained in experiments using certain herbicides.