Relationship between seed predation and activity-density of carabid beetles in farmland: A meta-regression

Carabid beetles are able to regulate weeds through seed predation. Our understanding of the role of carabids in arable crop systems is obscured by high variation across studies in weed seed removal and carabid abundance. Here we conduct an overarching synthesis of the relationship between seed removal and carabid activity-density. Using a database comprising 4919 data records from 25 published studies, we identify the average relationship between seed removal and carabid activity-density. With a mean carabid activity density of 3.11 beetles trap −1 day −1 and a mean seed exposure duration of 5.95 days, the probability of seed removal on sentinel seed devices was 35 %. We found that higher abundances are required to achieve more substantive seed removal rates, e.g., 17.04 beetles trap −1 day −1 for a removal probability of 80 % after one week of exposure. Such densities are rarely observed in the field, suggesting that carabid populations need to be promoted e.g., by more sustainable farming practices in order to provide higher weed seed predation rates. • For each carabid sampled per trap per day, the odds of seed survival decrease by 2.3 % • Methodological differences explain variation in carabid seed removal among studies • Achievable carabid densities could lead to effective seed control • Augmentation and conservation of carabids are essential for effective weed control