City bees do better than country bees

Wild bees do better in cities and suburbs than farmland, according to new research. The finding has implication for the ecological management of key pollinator species, and reveals agricultural land to be a poor source of bee-friendly nutrients and shelter.

A team of scientists led by biologist Ash Samuelson of the Royal Holloway University of London, in the UK, decided to investigate how environment affected the reproductive successful of the bumblebees (Bombus terrestris).

To do so, the researchers first caught 176 wild queens in London’s famous Windsor Great Park. After excluding any found to be carrying parasites, the insects were transferred to breeding boxes.

Eventually, 43 colonies were founded. These were then placed at carefully selected sites, ranging from the city CBD to suburban and village gardens, as well as nearby agricultural areas.

The scientists then visited each colony every week, monitoring reproductive frequency, food stores, disease and longevity. The results were correlated with land use patterns in the immediate vicinity.

Across all measures, the colonies established in the inner city and suburbs performed better than those in rural areas.

In a paper published in the journal Royal Society Proceedings B, Samuelson and colleagues say that they were not surprised bumblebee populations in suburban areas did well, “due to the combination of abundant gardens and proximity to semi-natural habitat”.

The same factors could not be advanced to explain the robust good health of the inner-urban colonies.

“We found no direct effect of the proportion of flower-rich habitat surrounding colonies on colony success,” the scientists write.

However, they concede that the absence of food sources in the mean streets of London might be more apparent than real. They note that measures of floral abundance “are not available because are not possible in urban areas due to access restrictions to gardens”.

They also cite a number of possible reasons to account for the poor performance of country colonies, including sparsity of food-flowers because of monocultured cereal crops, and exposure to agricultural chemicals.

Agricultural land, they suggest, may “represent a barren landscape for pollinators”, while densely developed cities, ironically enough, may function as refuges for such species.