When people talk about "Save The Bees!" they usually mean one specific bee: the European Honey Bee. In the US, honey bees are an introduced, domesticated species that we manage intensively, harvest bodily-produced products from, and keep in little beehive-barns. Like cows, only smaller and more stingy.

Depending on a single species for agricultural pollination puts us in a bit of a fix, though, when things go wrong. Native North American plants like squash and blueberries were pollinated for millennia by native species before Europeans showed up with their newfangled bees. How has plopping honey bees into the mix affected agricultural ecosystems? Which is more efficient at pollination, native bees or introduced honey bees?

) on blueberry flowers. Photo © H. Burrack

A new research paper measured just how much value-added native bees contribute to crops. For blueberries, they found it's not how many bees you have that are important, but how many kinds of bees that matters.

Honey bees are nice, but a farm that also has bumble bees, carpenter bees, and many small specialist bee species working their blueberry bushes gets more fruit. Farmers gain an estimated $311 per acre of fruit for each additional bee group foraging in their fields. “For North Carolina blueberries...we calculate the benefit of each group to be approximately $1.42 million worth of yield each year,” said Dr. Hannah Burrack, one of the authors on the study. That's per group of native bees. Promoting a highly diverse native bee population can be money in a farmer's pocket.

Blueberries are a fascinating crop to study; as a native plant, they have their own specialized crew of pollinators that co-evolved with them, such as the Southern Blueberry Bee. These bees specialize in buzz pollination; the bee essentially revs her wings to turn her body into a vibrator. That vibration bursts pollen loose from the male plant parts, dumping it on her face and body. Blueberries have oddly-shaped flowers, so sonicating bees do a much better job of pollinating than honey bees. Native bee species sonicate, but honey bees don't.

Image: USGS Bee Inventory

How do you investigate how much the work of a bee is worth? You spend a lot of time looking for bees and then watching them. The researchers had to make sure that a flower was only visited by one individual bee so they could measure how much fruit was set for each bee-visit (estimated by seed production, in this case.) When the flower in question is only 5mm long and there are hundreds of them on a shrubby plant, that makes things a lot harder.

. Like much of science, there is a lot of sitting around and waiting. Also sweating. Photo © H. Burrack

Once a bee visited a newly opened blueberry flower, an experimenter tied colored embroidery thread around the flower stem to mark the kind of species that visited each tiny flower in a cluster. Then they put a mesh bag over the flowers to prevent any additional bees from bringing in new pollen. Fifty days later, they went back, harvested the fruit, and spent a really, really long time counting tiny blueberry seeds as a measure of how well different bees pollinated the field.

Past research by this group looked at the individual efficiency of different bee species. Small native bees were highly efficient pollinators; their visits resulted in nearly twice as many seeds as honey bees. They also aren't as wimpy as honey bees, which only like to forage in nice sunny weather.

"A perfect bee would be super abundant, work under all weather conditions, and handle pollen efficiently. A perfect bee also doesn't exist," said Dr. Burrack. "We wondered if all these different bees, working together, can fill in the gaps and function as a perfect bee community." Essentially, each bee species is complimentary.

Honey bees are kind of wimpy when the weather isn't nice. Rain, cold, or high wind means the bees stay home. From Rogers et al. 2014. Honey bees are kind of wimpy. When the weather is cold, cloudy, and/or rainy, they stay home.

Honey bees are the most abundant bee in blueberry fields, but they are also the least efficient bee at pollinating blueberries, and fussy about when they will fly. Native bee species were more likely to fly when the weather was cloudy, cold or rainy. (Also, you find this out as an experimenter by sitting in the field when it is cloudy, cold, or rainy.)

All the different sizes and types of bees together result in a substantial benefit to the farmer. At some point in your education, you may have heard "diverse ecosystems are more stable and productive." It's difficult to think of an ecosystem less diverse than an agricultural field, but they are still a living system.

The biodiversity of our native ecosystems provides a kind of 'biological insurance.' Pollination by wild bees is a valuable ecosystem service we humans get for free. Farmers know this and want to learn more, which is why this research was supported in part by the North Carolina Blueberry Council.

Honey bees aren't actually necessary for all crops. In watermelons, honey bees didn't deposit a significant amount pollen on flowers; native bees provided nearly all pollination services. In tomatoes, native bee species increased fruit production significantly. Instead of focusing exclusively on honey bees, taking care of our native species is probably the best way to build and support a resilient agriculture. You can find some tips for making these native species welcome in your yard and garden here.