MSc Wencke Ladwig

Previous studies had indicated that the densities of granivorous beetles in the state of Mecklenburg-Vorpommern (N-Germany) are so low that they might be limiting weed control via seed predation. If so, enhancing beetle densities should lead to higher predation rates. Furthermore, an observation in a greenhouse experiment seemed to suggest that seed predation by granivorous beetles is lower when carnivorous beetles are present than when they are absent.

To confirm or reject these hypotheses, I conducted a field study using 1 m² enclosures that allowed the artificial manipulation of beetle numbers and identity in the field, and seed cards to estimate seed consumption. The purpose of my study was to investigate

1) if densities of granivorous carabid beetles in arable fields are limiting predation of weed seeds, and

2) if seed predation rate by granivorous beetles is influenced by the presence of carnivorous beetles

Over a period of 23 days, about 4% of the seeds of Poa annua and Stellaria media were consumed when a natural density of beetles was present (approx. 5 carabids per m2), confirming earlier observations made in Mecklenburg-Vorpommern. When instead the exclosures contained 10 granivorous beetles (two Harpalus rufipes and eight Harpalus affinis), seed predation rates increased to 16.5%. When both granivorous and carnivorous beetles (two Pterostichus melanarius and eight Poecilus cupreus) were present, predation rates decreased to 14.2%.

Consequently, augmentation of carabids did enhance seed predation rates. However, we could find no proof that carnivorous beetles would interfere with the activity of the granivorous carabids.

Wencke Ladwig. Einfluss carnivorer Laufkäfer auf die Samenprädation durch granivore Laufkäfer in einem Winterweizenschlag. MSc thesis Universität Rostock 2012.

Supervisor; Friederike de Mol,Paula R. Westerman

Project duration; June – August 2012