The Pollinating Power of Bumble Bees

By Molly Jameson

There are five social species of bumble bees (Bombus spp.) native to Florida, and each is an important pollinator throughout the state. European honeybees provide about 85 percent of our pollinating activity that is vital for supplying one-quarter to one-third of our food supply.  Bumble bees, however, are also very important for pollination. More well known for their ability to pollinate native and ornamental plants, they can also pollinate a variety of food crops, including tomatoes, peppers, cucurbits, strawberries, blueberries, fruit trees, cover crops, and more.

An American bumble bee pollinating white clover. Bumble bees are efficient pollinators of many crops and cover crops. Photo by B. Merle Shepard, Clemson University, Bugwood.org.

One way bumble bees outshine honeybees is in their ability to “sonicate” or “buzz pollinate” certain flowers, such as tomatoes, peppers, and blueberries. For instance, although tomatoes are self-pollinating (each flower contains both male and female plant parts), their flowers must be vibrated by wind or insect in order to release pollen for fertilization. When bumble bees land on a tomato flower and vibrate their bodies, it shakes pollen from the anther (the male part of a flower) to the stigma (the female part of the flower), resulting in pollination. Honeybees are not capable of vibrating at the frequency needed to open a tomato flower. Although wind also pollinates tomatoes, studies have shown that pollination by native bees can increase tomato fruit set by nearly 50 percent more than with wind alone! Additionally, native bees help cross-pollinate tomato plants, leading to larger tomatoes and an increased overall yield.

Another advantage bumble bees have over honeybees is in their pollination efficiency. For certain crops, such as strawberries, bumble bees are two-and-a-half times more efficient at pollination than honeybees. Some species of bumble bees also have a longer tongue than honeybees, which allows them to pollinate certain flowers, such as red clover, more effectively.

Here in our sub-tropical humid climate in North Florida, we experience many rainy and cloudy days throughout the year. On these days, honeybee foraging decreases significantly. Bumble bees, however, have larger bodies with more hairs that allow them to regulate their body temperatures more efficiently. This gives them the ability to forage for pollen and nectar on days honeybees are inactive.

A diversity of native pollinator plants supports a diversity of native pollinators. Photo by Rachel Mathes.

Although it is very common for farmers to import honeybee colonies onto their farms to increase pollination rates, importing bumble bee colonies for open field crop pollination has had mixed results. Imported bumble bee colonies can, however, be very useful in closed settings, such as greenhouse tomato or cucurbit production. It may seem intimidating to work so closely to stinging insects, but bumble bee colony breeders select for mild-mannered bumble bees that pose little threat to greenhouse operators.

In open field settings, it is much more effective to harness the pollinating power of bumble bees by providing a diversity of nectar and pollen-rich plants to support wild bee colonies. Bumble bees are generalists, meaning they will visit a wide variety of flowers to suit their needs. Native plants provide the best sources of nutritious nectar and pollen for bumble bees and other native pollinators. Native wildflowers such as goldenrod, Coreopsis, Elliott’s aster, purple coneflower (Echinacea), thistle, Spanish needle, tickseed, swamp sunflower, dotted horsemint, and ironweed – among many others – are great nectar sources for native Florida bumble bee species. A few hedge rows, pollinator strips, or uncultivated farmland containing these plants can encourage bumble bees to inhabit the area. If purchasing a wildflower seed blend, be sure the mix is suitable for our area and does not contain invasive or weedy plant species.

Along with providing pollen-rich areas, it is also important to provide a place for queen bumble bees to nest. Nesting sites for bumble bee queens can be as simple as an old tree stump, a pile of leaves, or a hole dug by a larger animal. You can also install bumble bee nest boxes around the farm to encourage inhabitation. Lastly, help support pollinators by minimizing the use of insecticides – especially while flowers are present – and look for formulations that are least toxic to bees and other pollinators. By supporting pollinators and pollinator habitats, we also support our food supply, economy, and our environment.