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The Carpathian Basin was until the middle of the 20th century an important territory for locust outbreaks. This paper combines the earlier data and our own research related to the present status of three most important locust species of the period mentioned. It appeared that during the 19th and 20th centuries populations of Calliptamus italicus and Dociostaurus maroccanus generally decreased, and even Locusta migratoria lost its earlier economic importance in the Carpathian Basin/Hungary. In any case, the extensive and deleterious outbreaks known especially from the 14th to 19th centuries seem to stop in the Carpathian Basin. Beside the large waterway-regulations (= drying up the Pannonian Plain), the rapidly intensified agriculture might be the main reason for stopping of the earlier deleterious outbreaks and damages caused by L. migratoria, however, the desiccation of the Pannonian Plain temporarily created favourable habitats for extensive outbreaks of D. maroccanus and other xerothermous (e.g. C. italicus) species. Environmental changes evoked by a new trend in the agricultural land-use, in making extended surfaces of uncultivated (set-aside) lands/fallows, seem to provide suitable habitats for scattered local outbreaks in the future too, as was the case in 1993 with the Moroccan locust in Central Hungary.

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The various essential spectra of a linear operator have been surveyed byB. Gramsch andD. Lay [4]. In this paper we characterize the essential spectra and the related quantities nullity, defect, ascent and descent of bounded spectral operators. It is shown that a number of these spectra coincide in the case of a spectral or a scalar type operator. Some results known for normal operators in Hilbert space are extended to spectral operators in Banach space.

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