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Organic cropping practice decreases pest abundance and positively influences predator-prey interactions
- Jacobsen, Stine K., Moraes, Gilberto J., Sørensen, Helle, Sigsgaard, Lene
- Agriculture, ecosystems & environment 2019 v.272 pp. 1-9
- Araneae, Hymenoptera, Phytoseiidae, Tetranychus urticae, Urtica dioica, agroecosystems, habitats, herbaceous plants, insect pests, leaves, natural enemies, organic production, parasitoids, phytophagous insects, predator-prey relationships, predatory mites, species abundance, species richness, strawberries, vegetation
- Cropping practice influence arthropod species abundance and diversity in agroecosystems, thus impacting populations of insect pests and their natural enemies. A field study was conducted to investigate whether pest and natural enemy abundance was higher in organic compared with conventional strawberry fields, and whether the non-managed vegetation surrounding the field impacted natural enemy abundance and diversity in and around the field sites. The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and predatory mites were sampled from strawberry leaflets and the leaves of wild herbaceous plants from the surrounding vegetation. Insect predators, hymenopteran parasitoids, spiders and herbivores were collected from the same habitats. Abundance of T. urticae was ten-fold higher in conventional compared to organic strawberry fields, whereas the ratio of spider mite to predatory mites was 9.5 times lower in organic compared with conventional strawberry fields. The 14 species of predatory mites identified were all from the family Phytoseiidae, and predominantly found on stinging nettle, Urtica dioica L. (Rosales: Urticaceae) (> 80% of individuals), in the surrounding vegetation. There was no significant effect of cropping practice on the density of insect predators and spiders, while the density of insect parasitoids and insect herbivores was higher in the organic compared to the conventional sites. Total species richness at the edge of organic fields and in the surrounding vegetation of both organic and conventional sites was higher than in the other sampling sites. This study demonstrates the major impact of cropping practice on T. urticae abundance and on the prey to predator ratio, whilst also emphasizing the importance of the surrounding vegetation as a source of natural enemies of phytophagous arthropods.