Foraging trip duration of bumblebees in relation to landscape-wide resource availability

1. The study tested the hypotheses that bumblebees have shorter foraging trips in environments that provide abundant resources than in environments that provide sparse resources, and that shorter foraging trips translate into greater colony growth. 2. Six even-aged Bombus terrestris colonies were established in contrasting resource environments. Three colonies had access to abundant resources (Phacelia tanacetifolia fields with high flower densities), and three colonies were placed in an environment with sparse resources (scattered semi-natural habitats with food plants at lower densities). 3. A total of 870 foraging trips of 220 marked B. terrestris foragers were observed using automated camcorder recordings. 4. The duration of foraging trips was shorter in environments with abundant resources (66 +/- 4.6 min) than in environments with sparse resources (82 +/- 3.7 min). Within 34 days colonies that had access to abundant resources gained significantly more weight (129 +/- 40 g) than colonies foraging on sparse resources (19 +/- 7 g). 5. Thus, the spatial distribution and quality of resources at landscape level affected the duration of foraging trips and the colony growth. It was concluded that future conservation schemes need to improve the spatial and temporal availability of resources in agricultural landscapes to counteract the ongoing decline of bumblebees.