Predators as biological control agents in winter oilseed rape fields-results on predators from the EU-Project MASTER

摘要

The results from our research laboratory and field experiments indicate that there is a reziproke correlation between predator density and pest problems. It could be shown:1. the ICM system leads during the time of pest attack and larval dropping to an increase of the numbers of ground beetles (Coleoptera: Carabidae) in oilseed rape as well as in the subsequent crop winter wheat Thus, the ICM-system shows advantage to maintain biodiversity.2. in all years the activity densities of ground beetles and spiders were significantly higher in the ICM system.3. there are spatio-temporal associations between certain predator species and pest species which in most cases are clearly related to the management intensity.4. comparing the hatching rates of the new pest generation, differences between die ICM and STN systems (part in respect to insecticide treatments) are not significant This demonstrates the effectiveness of natural enemies and can be judged as a plus for the ICM-system in which no insecticides where applied.5. if a comparatively high no. of Staphylinidae-larvae occurs at the right time (coincidence with peak of Meiigethes-larvae) and the abundance of Meligethes-larvae is comparatively low, the effect of predacious rove beetle larvae on Meligethes spp. population development is higher as that of insecticide applications. Thus, under certain circumstances Staphylinidae-larvae can replace insecticide treatments.6. Integrated crop management (ICM) seems to promote building of horizontal webs of Linyphiid-spiders and is an indicator of their higher abundance and presence in the field. As main factor reduced tillage could be identified.7. Thus, the Integrated Crop Management system ICM promotes predators by the following three key features:1. Lowo insecticide use. 2. Reduced tillage (mulching). 3. Less distance to landscape structures like hedgerows, extensively managed field margins or fallows. Regardless of that there was a 10% - 20% higher yield in recorded in STN systems. In the average of 4 years a (ploughed) STN-system with reduced insecticide applications (2,0 insecticide applications in a more extensive STN system vs. 5,0 in a more intensive STN system) shows best yield. However, due to costs farmer reduce ploughing in oilseed rape anyhow, so a mixed system of ICM and STN would be most realistic and promising.8. Furthermore the following results with practical implications were achieved:9. Staphylinidae-larvae (Tachyporus spp.) are in connection with population development of Meligethes snp, an object for a phenological model within decision support systems.10. The reputation of Amara similata (Coleoptera: Carabidae) as more or less strictly phytophagous and non- relevant as predator could be clearly revised. A. similata seems to be an important predator with clear preference to Dasineura brassicae. Amara similata obviously has skills to detect D. brassicae-larvae from outside in pods which are still closed This has implication on the practice as for example in France Amara similata was judged as pest as this species was seen climbing up the oilseed rape plant and feeding on pods and controlled with insecticides Now it is clear that they attack only pods infested by Brassica pod midge which loose their seeds anyway by splashing early through the toxin secretion of the pest larvae.