Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca)

Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.     

Variance in leaf spot susceptibility in chestnut trees of different species and hybrids

Journal of Plant Diseases and Protection - Prior to the first occurrence of chestnut blight in 1976, leaf spot caused by Cylindrosporium castaneae was one of the most important diseases of European...     

Entomofauna jetele (Trifolium pratense L.) a jejívývoj. Entomofauna des Kleefeldes (Trifolium pratense L.) und ihre Entwicklung

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LATEX paint as an antifeedant againstHylobius abietis (L.) (Col., Curculionidae) on conifer seedlings

LATEX paint in water solution applied to newly planted conifer seedlings was found to prevent damage byHylobius abietis adult weevils for the whole season. Treatment of the basal third of the trunk was sufficient. Also, utilisation of the results as a model for deerantifeedant treatments and protection againsts the weevils is recommended.With 1 figure     

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Experimentelle Infizierung einiger anБereuropäischerPinus-Arten durch die KiefernnadelgallmückeThecodiplosis brachyntera (Schwägr.)(Diptera,Cecidomyiidae)

Zusammenfassung Die KiefernnadelgallmückeThecodiplosis brachyntera (Schwägr.), die in Europa anPinus sylvestris L.,P. mugo Turra undP. nigra Arnold lebt, wurde im Arboretum Bolevec in Westböhmen auch an der nordamerikanischen KiefernartPinus resinosa Aiton und den ostasiatischen KiefernartenPinus tabuliformis Carriere undP. yunnanensis Franchet festgestellt.Experimentell gelang es durch die Kiefernnadelgallmücke vonPinus mugo subsp.mughus (Scop.) Domin, auch die obengenannten außereuropäischen Kiefernarten und als Kontrolle die europäischen ArtenPinus sylvestris L. undPinus mugo subsp.uncinata (Ant.) Domin zu infizieren. Experimentelle Infizierung war erfolglos an den Kiefernarten:Pinus cembra subsp.alpina (Rikli),P. strobus L.,P. rigida Miller,P. radiata D. Don.,P. echinata Miller,P. contorta Douglas undP. thunbergii Parlatore.Die Ursache der Nichtinfizierung der untersuchten Kiefernarten kann folgenden Ursprung haben: Unterschiede in dem Chemismus, besonders in der Qualität und Quantität der Terpene im Innern der Nadeln, oder: Unterschiede in der Gestalt der Nadeln, besonders die Nichtanwesenheit der Nadelscheide, die den Basalteil der Nadeln umhüllt und deshalb die Entwicklung der Eier und Larven nicht ermöglicht, oder aber: es waren morphologisch die Nadeln in der Zeit der Infizierung für die Eiablage nicht geeignet — entweder noch mit Schutzschuppen bedeckt, oder schon zu groß entwickelt.Die befallenen Nadeln der außereuropäischen Arten waren verkürzt, in dem Basalteile grö ßtenteils einige mm zusammengewachsen. Die Lavalkammer befand sich in der Mehrzahl der Fälle in der Nadelbasis.Nach den gewonnenen Ergebnissen erscheint es notwendig, eine taxonomische Revision der 5 von 11 nordamerikanischen Kiefernarten beschriebenen Gallmückenarten durchzuführen.

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Summary The Needle shortening gall midgeThecodiplosis brachyntera (Schwägr.) occurring in Europe on the pinesPinus sylvestris L.,P. mugo Turra andP. nigra Arnold was found in an Arboretum in Bolevec in Western Bohemia on the North American speciesP. resinosa Aiton and on the East Asian speciesP. tabuliformis Carriere andP. yunnanensis Franchet.The following non-European species:Pinus resinosa Aiton,P. tabuliformis Carriere andP. yunnanensis Franchet and European species:P. sylvestris L. andP. mugo subsp.uncinata (Ant.) Domin were experimentally infested withThecodiplosis brachyntera (Schwägr.) fromPinus mugo subsp.mughus (Scop.) Domin. The experimental infestation was not successful in the case ofPinus cembra subsp.alpina (Rikli),P. strobus L.,P. rigida Miller,P. radiata D. Don.,P. echinata Miller,P. contorta Douglas andP. thunbergii Parlatore.The failure to infest some pine species might have three causes: the chemical compositions of the pine needles differed; the sheath shielding the basal part of brachyblast was missing; the needles of some pine species were not in the right state for oviposition and development of larvae at the time of infestation — they were either too mature or completely covered with scales.Infested needles of the non-European species were considerably shortened compared with non-infested ones. Their basal part usually coalesced for several mm and in most cases the larval chamber was situated right in the base of the needle.Results mentioned above showed the necessity of revision of the taxonomic position of 5 gall midge species developing in the bases of 11 North-American pine species.

     

Metody Chovu Hmyzu

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The expansive Russian wheat aphid,Diuraphis noxia (Mordw.) detected in the Czech Republic

The Russian wheat aphid,Diuraphis noxia (Mordw.) has been detected in southern Moravia, the Czech Republic in June, 1995. Its location is related to its incidence in central Hungary. The further predicted area of distribution covers the grain-maize growing districts of southern Moravia (Czeck Republic), neigh-bouring parts of Austria, southern and south-eastern parts of the Slovak Republic. The aphid is classified as a species expanding to the north from its mediaterranean area of distribution, apart of extensive areas (North to South Americas, S. Africa, expected in Australia) which it has covered thorugh accidental introductions and further spread over the world.     

Der Einfluß von Systox auf einige Insektenarten des Zuckerrübenfeldesvon Systox auf einige Insektenarten des Zuckerrübenfeldes

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