The role of field defects for ground beetles (Coleoptera, Carabidae) diversity and ecosystem services in oilseed rape

GONZÁLEZ, EZEQUIEL; SEIDL, MIROSLAV; STROBL, MARTIN; KADLEC, TOMÁS; SASKA, PAVEL; KNAPP, MICHAL

Halle

Congreso; German Entomology Congress; 2019

Agricultural landscapes under an intensified production are characterized by species losses and homogenization of communities. Therefore, fragments of non-crop habitats immersed in these landscapes are fundamental because they can act as refugees for important groups such as insects and thus be relevant elements for biodiversity conservation. At the same time, these non-crop habitats can also act as sources of beneficial organisms and ecosystem services for adjacent crops. Among the different types of non-crop habitats, field defects are temporary patches where sown plants are poorly developed and other plant species can emerge. These defects can be common and relatively large in years with extreme weather conditions. However, their relevance as habitat for beneficial insects and ecosystem services for crops is unknown. Here, we investigated the species richness and activity-density of ground beetles (Coleoptera, Carabidae) and quantified two ecosystem services closely linked with their activity (pest and weed seed predation) in field defects within oilseed rape fields. Furthermore, we evaluated the relationship between ground beetles abundance and ecosystem services in order to test their contribution to these important services for crops. Ground beetles were sampled in 20 fields located in the central region of the Czech Republic on two occasions using pitfall traps in three habitats within each field: field defects, field interiors and crop-defect boundaries. Ecosystem services were measured in 10 of these fields using artificial caterpillars made of plasticine and seed cards of two common weed species (Taraxacum sp. and Stellaria sp.). We used GLMMs for statistical analyses. In total, 27076 individuals from 72 species of ground beetles were collected. Species richness of carabids was lower in field defects than within fields and boundaries and increased in the second sampling period. Activity-density showed a similar pattern but a significant interaction between habitat and sampling period was found: the increase in number of individuals during the second period was higher for field interiors. Mean pest predation rate was 50%, with small mammals (55% of attacks) and insects (44%) as the dominant predators. Total pest predation and predation by insects increased in the second period but did not differed between habitats. Predation by small mammals was similar across habitats and sampling periods. Insect predation was positively related to the abundance of medium and large carnivorous carabids. Seed predation rates were similar for Taraxacum (27%) and Stellaria (25%) and, for both species, there was an interaction between habitat and sampling period, with stronger differences between habitats in the first period. Predation of Taraxacum seeds was related to the abundance of large omnivorous carabids, while predation of Stellaria seeds was positively linked to medium omnivorous carabids and negatively to large herbivores. This research was supported by grant GAČR 18-26542S.