WP3 - Population development of solitary wild bees, bumblebees and honeybees
To investigate the effects of organic farming, semi-natural habitats and flower strips on populations of wild bees and honeybees, 1) trap-nests for cavity-nesting bees and wasps, 2) bumblebee colonies and 3) honeybee colonies will be placed in the center of the study landscapes and the population development of the colonies will be recorded.

1) Trap-nests
Cavity-nesting bees, wasps, and their natural enemies can be recorded in a standardized manner using nesting trap-nest. To investigate the interactions between landscape factors (proportions of organic farming, semi-natural habitats and flower strips) on the population development of wild bees and their natural enemies, we will set up four posts with two trap-nests each in the center of the study landscape in March/April 2022. In September 2022, the nest boxes will be brought to the lab to determine population size, parasitism rates, and hatching success.

2) Bumblebee colonies
Bumblebees are active for extended periods of time as they build their colonies over several generations of workers. They also have a broad food spectrum. Therefore, in addition to stem-nesting bees active over shorter periods of time, we plan to study colony development and reproductive success of bumblebees (B. terrestris L.). Two young B. terrestris colonies will be established in the center of the study landscapes. We will regularly record the weight gain of the bumblebee colonies and also the presence of counterparts and the reproductive success of the bumblebees.

3) Honeybee colonies
Honeybees are also generalist flower visitors that are active over an extended period of time. We will establish four young honeybee colonies in the center of each landscape. We use young colonies because they have shorter collection distances than large economic colonies and thus their development is more dependent on resource availability in the surrounding area. At monthly intervals (about every 4 weeks), various parameters of colony development are recorded (including colony strength and parasite infestation).