Comparison of flower constancy and foraging performance in three bumblebee species (Hymenoptera: Apidae: Bombus)

The three bumblebee species Bombus terrestris (Linnaeus 1758), Bombus lapidarius (Linnaeus 1758), and Bombus pascuorum (Scopoli 1763) showed consistent differences in their respective levels of flower constancy when foraging on three different pairs of flower species. B. terrestris was always the most flower constant, followed by B. lapidarius, with B. pascuorum the least flower constant species. These interspecific differences in flower constancy were related to foraging performance under field conditions near Würzburg, Germany in 1999 and 2001. B. terrestris was more flower constant, and predominantly outperformed B. lapidarius at collecting nectar in both years. As B. terrestris is also the larger of these species, these data also support the idea that larger bees are more efficient at nectar foraging, i.e. they bring home more nectar per unit time. However B. pascuorum, the least flower constant of the three species tested, was the most efficient of them at collecting nectar, collecting 50% more nectar than B. terrestris per hour. Therefore flower constancy appears to be a relatively poor predictor of species foraging performance, which is likely to be influenced simultaneously by many other factors including worker body size, tongue length, and foraging range