Landscape-scale floral resources and bumblebee survival

Red-tailed bumblebee, Bombus lapidarius. Photo by Lucy Hulmes.

This week's paper is in Nature, lead authored by Claire Carvell who is a Senior Ecologist at the UK's Natural Environment Research Council's (NERC) Centre for Ecology & Hydrology. Bumblebees are important pollinators for many wild and agriculturally important plants (think apples, strawberries, blueberries, tomatoes, etc.). There has been a global decline in bumblebee populations over the recent decades, likely caused by multiple factors that include disease, pesticides, (and most relevant here) agricultural intensification. As agricultural land use becomes more and more uniform (think those vast fields of wheat or corn), the diverse array of floral resources that bees need becomes less and less available. Other studies have examined how flowering strips or hedgerows impact bumblebee density and pollination services to flowering crops. This study addressed the same question but they investigated the effect on bumblebees across generations. 

What they did

In Buckinghamshire, England there is 1000 hectares of farm land with edges sown with wildflower seeds such that each 50 hectare block has 0% to 8% coverage of wildflowers. In this habitat Carvell and her colleagues studied three bumblebee species Bombus terrestris, B. lapidarius, and B. pascuorum. Across this area in 2011 they captured bumblebees of all three species, collected DNA samples, and then used the genetic information to determine which bees were from the same colony. Using the collection locations of worker bees they were able to determine the most likely colony location. They assessed the area surrounding each colony location for floral resources. The next spring 2012, they captured the emerging queens who were out looking for new nest sites, collected their DNA to determine which colony they had come from, and determined how far they had dispersed from that colony.

What they found

When there were more flowering resources surrounding a colony (within 250 meters, 500 meters, and 1000 meters), more of that colony's queens were seen the next spring. They refer to this as "family lineage survival" because it is across generations. When workers are able to forage on flowers close to their colonies, they are able to collect more resources and produce more new queens. Colonies that have to forage further for food do not produce as many new queens. Interestingly, the distance that queens dispersed was not affected by flowering resources, but was affected by nesting habitat availability. When there was more suitable nesting habitat 250, 500, and 1000 meters from their parent nests queens dispersed further. This is a bit counterintuitive, you would think that if there was more suitable nesting habitat close to home queens would not have to disperse as far. But the authors suggest that the nesting habitat "facilitates" dispersal, perhaps by providing shelter for queens as they disperse?

The takeaway

I really like the way that this study used genetics to look at performance of whole colonies, and the next year's queens. That is a cool step from other studies that have just looked at numbers of individual bumblebees. It is always reassuring that something can be done to mitigate species declines, the next task is providing land-owners with suitable wildflower seeds, especially local genotypes of native species!