Honeybees (Apis mellifera) are important pollinators of flowering plants but have come under increasing pressure in recent times due to habitat loss, pesticide use and the emergence of diseases. Recent evidence suggests that flower-rich gardens in towns and cities may play an important role in providing food to bees and in the conservation of these pollinators.
In the past, it has been difficult to assess the extent to which urban flower patches provide resources to honeybees because the majority of the gardens are on private property and are not easily accessible. Similarly, it is challenging to determine the floral species richness in agricultural lands where small patches of wildflowers provide important food in a sea of otherwise unappetizing crop fields. This makes it impossible to quantify accurately the resources available to bees in the two habitat types.
In a recent study, researchers from Royal Holloway University and Virginia Tech used the characteristic waggle dance, displayed by honeybees when they return to the hive, to determine the distance bees travel to find suitable food. Using this method, they established that bees foraging in rural or agricultural areas had to travel farther to find food than did bees that foraged in urban settings.
“In this study, we overcame the hurdles of assessing floral resources by getting the bees themselves to tell us where to find food,” said Professor Elli Leadbeater. “Calculating the distance to forage indicated by the waggle dances provides a real-time picture of current forage availability, from the bees’ own perspective.”
When a bee returns to its hive after a successful foraging trip, it displays a waggle dance on the hanging honeycomb to communicate information about available food to the other bees. The dance takes the form of a figure of eight, with the duration of the central run indicating the distance to the food and the angle indicating the direction.
The researchers decoded 2,827 waggle dances from 10 western honeybee colonies in London and 10 in surrounding agricultural areas in Kent, Surrey and other counties. This information allowed the researchers to map out where the bees had been to collect their food. They calculated that bees in urban areas had an average foraging distance of 492 meters, whereas bees in agricultural areas traveled an average of 743 meters to their food.
“Our findings support the idea that cities are hotspots for social bees, with gardens providing diverse, plentiful and reliable forage resources. In agricultural areas, it is likely harder for honeybees to find food, so they have to go further before they find enough to bring back to the hive,” explained Professor Leadbeater.
The researchers also found no difference in the amount of sugar collected by the urban and rural bees during their foraging trips. This indicated that the rural bees were not travelling further in order to access remote, nectar-rich sources of food; they were simply traveling further because there is less available food in agricultural areas.
In terms of bee conservation, the authors of the study warn that urban areas make up such a small percentage of total land cover that they will not be sufficient to support bee populations suffering from food paucity in areas dominated by intensive agriculture.
“Conservation efforts should be directed towards increasing the amount of non-crop flowers in agricultural areas, such as wildflower strips,” said Professor Leadbeater. “This would increase the consistency of forage available across the season and landscape as well as minimize bees’ reliance on small numbers of seasonal flowering crops.”
She also emphasized that because the study focused on honeybees only, the findings do not necessarily apply to all bee species. “While we can potentially extrapolate our results to some wild bees, such as generalist bumblebee species, our results should not be used to imply that this pattern will hold for all bee species. For many solitary bees, the existence of specialist host plant species or nesting sites will be important in determining whether cities are valuable habitats.”
The study is published in the British Ecological Society’s Journal of Applied Ecology.