Ziel des Reduktionsprogramms chemischer Pflanzenschutz ist es, die Anwendung von Pflanzenschutzmitteln (PSM) auf das notwendige Maß zu begrenzen (Backhaus & al. 2005). Als geeigneter quantitativer Indikator für die Kennzeichnung der Pflanzenschutzmittel-Anwendungsintensität findet der Behandlungsindex Verwendung. Praxisstudien sollen zeigen, wie sich eine längerfristige Reduktion der Anwendung von PSM auf betrieblicher Ebene auf den ökologischen Status quo von Ackerflächen auswirkt.Reduction programs are designed to reduce chemical plant protection to a minimum. The intensity of plant protection can be measured by the treatment frequency index (BI). This study is interested in the ecological impact of a long-term reduction of chemical plant protection in commercial crop cultures. It investigates the effects of a 50 % treatment reduction on Araneae at three fields in Ochtmersleben (Saxony-Anhalt). In 2003, data collection focused on fields of winter wheat (100 % application, BI 3.5 vs. 50 % application, BI 1.9), spring wheat (100 % application, BI 4.6 vs. 50 % application, BI 0.8) and sugar beet (100 % BI 5.4 vs. 50 %, BI 2,7). In 2004, plots of winter wheat (100 %, BI 5.4 vs. 50 %, BI 3.3), spring wheat (100 %, BI 5.8 vs. 50 %, BI 4.0) and peas (100 %, BI 2.9; 50 %, BI 1.4) and in 2005: winter wheat (3.8 vs. 2.1), pea (4.1 vs. 2.2) and winter wheat (6.25 vs. 3.3) were investigated. Insecticides were applied in 2004 and 2005. In 2003-2005, 11,120 spiders belonging to 60 species out of 14 families have been documented. Activity density peaked in the 50 % variant of fields 1 - 3 (field 1: 2,373, field 2: 1,908, field 3: 1,940 spiders). It was lowest in field 3 (100 %) with 1,564 spiders. In 2003, a total of 6,951 spiders belonging to 41 species out of 12 families were caught in pitfall traps during the period 01/06/03 - 27/06/03. Activity density peaked in the 50 % variant of winter wheat with 1,427 individuals. It was lowest in both sugar beet variants (100 % variant: 891 specimens, 50 % variant: 1,074 specimen). The impact of plant protection on the spider activity was stronger when the measures were applied at an early date. The intensity of plant protection also influenced the species diversity (e.g. sugar beets 50 % variant: 15 species; 100 % variant: 10 species). In 2004, 1,341 spider individuals were collected during the period 01/06/04 - 06/07/04. The massive 80 % drop of spider activity compared to the previous year was likely due to the application of insecticides. A total of 41 species belonging to 12 families were identified. Again, Araneae activity peaked in winter wheat (650 specimen), followed by spring wheat (435 specimen) and peas (256 specimen). In 2005, a total of 2,828 individuals (Araneae) belonging to 38 species out of 9 families were identified (collecting period 08/06/05 - 06/07/05). More individuals (986) were found in winter wheat (50 %, field 1) compared to winter wheat (50 %, 659 species, field 3) and peas (50 %, 238 species, field 2). The results indicate that the impact of insecticides on the spider population was stronger the earlier insecticides were applied. In summary, a long-term reduction of chemical plant protection of 50 % did have positive effects on spider coenoses
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