2. Beziehungen zwischen Schaedlingen und Nuetzlingen in Agraroekosystemen unter Beruecksichtigung der Wechselwirkungen zwischen Produktionsstandort und Randbiotopen sowie des Einflusses von Pflanzenschutzmitteln. 2.3. Die Regulation der Populationsdichte von Getreideblattlaeusen durch Antagonisten: Einflussfaktoren.
1994
Groeger U. | Ohnesorge B.
The population dynamics of cereal aphids and their antagonists were monitored at two sites near Stuttgart: at Hohenheim (narrow cereal fields, many extensive orchards, gardens and woods) and Muenchingen (large fields, relatively few refuges for antagonists). During winter and spring, winter barley and roses, during summer, winter wheat fields were examined. By trap plants (potted wheat plants which were artificially infested with aphids) the first appearance and the spatial distribution of antagonists were monitored. The investigations yielded the following results: - Survival of hibernating virgins of Sitobion avenae was governed by winter temperature: In 1988/89 many virgins survived (minimum temperatures at soil level always above -10 degrees C), in 1990/91 practically no virgins survived (minimum temperature near -20 degrees C. - Early leaf fall in autumn 1989 reduced considerably oviposition of Metopolophium dirhodum on the winter host rose. - Intensity of immigration governed the dormancy among cereal aphid species and, to a smaller extent, the resulting local density of aphid population. It was not responsible for the from year to year changing intensity of aphid outbreaks. - Syrphids proved to be the key factor in winter wheat. The temporal course of their oviposition was crucial for their efficiency: A temporary reduction during the period of maximum aphid population growth, which was caused by cold and wet weather, triggered in June 1990 a serious cereal aphid outbreak - a rare event in the area of Stuttgart. - Syrphid females ready for oviposition are present very early in the year. Trap plants in the vicinity of antagonists refuge habitats caught syrphid eggs early in March, in wheat fields from the beginning of May onwards.
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