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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.

Description / Table of Contents: Summary The occurrence, phenology, and importance of natural enemies of the Colorado potato beetle Leptinotarsa decemlineata (Say) was studied near Belleville, Ont. Canada) in 1956. Specific predators. Perillus bioculatus (Fab.), and parasites, Doryphorophaga doryphorae (Riley), were most important. The mortality of egg and larval instars of the pest up to the mature L4 was observed quantitatively on plants partly unprotected, partly semiprotected and caged (total population counted: 12.800 eggs). Comparison of results showed that birds and running predators are of no particular importance as limiting factors; flying predators, however, reduce the survival of L4 from about 46% to about 23%. Parasitization by D. doryphorae was low at the beginning (0–5%), but increased later up to 50%. The time-coincidence of host larvae and parasites was very poor and no second generation of the beetles occurred. The tachinid probably hibernates as puparium in the soil. The total mortality of potato beetles at Belleville, 1956, was insufficient to avoid defoliation. From this might be concluded that integration of biological and chemical control methods will be advisable in Central Europe. Further studies are necessary before another attempt of colonizing natural enemies of the potato beetle in Europe can be recommended.

Description / Table of Contents: Steel embrittlement by hydrogen sulfideTensile tests in a pressurized vessel filled with hydrogen sulfide and its mixtures with air or hydrogen show, that at 18 and 130 at hydrogen sulfide produces steel embrittlement in a way comparable to hydrogen; the extent of embrittlement, however, is considerably higher in the case of hydrogen sulphide. Addition of air does not show any influence on embrittlement, while in mixtures with hydrogen embrittlement is less pronounced than under the effect of the pure components. When carrying out such experiments it is necessary to take into account that the experimental apparatus is contaminated by hydrogen sulfide for some time after the experiments, so that during subsequent experiments with pure hydrogen a side effect due to hydrogen sulfide must be expected; this means that in such cases the values obtained are below those obtained for embrittlement in pure hydrogen.