Flower Damage From Bumblebee Pollination

Nectar-Robbing

• Damage to flowers is caused by a practice known as nectar robbing. Many pollinating species display this behavior, including hummingbirds, ants, moths and bumblebees. Nectar-robbing species poke holes in the bases of flowers' corollas or the nodes where petals emerge. These species then suck out the flowers' nectar. With their short tongues, bumblebees are often responsible for creating initial holes in flowers. Other species of bumblebees, moths and honeybees, known as secondary robbers, may then visit the holes and steal nectar.

Problems

• Though the tiny holes cause some damage, the real problem associated with nectar-robbing bumblebees stems from lack of pollination. When bumblebees extract nectar directly from bases of flowers, they don't come into contact with pollen. In contrast, other pollinators access nectar through the tops of the flowers, thus coming into contact with the flowers' reproductive organs. The pollen is carried on to other flowers and the pollination process is underway. When pollination does not occur, fewer seeds and fruits are produced.

Case Study

• In a 2001 study in "Oecologia," a scholarly journal that publishes ecological studies, researchers explored the relationship between damage to monkshood or Northern wolfsbane (Aconitum lycoctonum) and a specific type of bumblebee known as nectar-robbing, short-tongued bumblebees (Bombus wurflenii). These bees bore holes through flowers' petals to remove nectar, a practice which causes damage to petals. However, the study found that not only do these nectar-robbing bumblebees rarely damage the reproductive or nectar-producing capacities of the plants, but that they only caused damage at high elevations.

Benefits

• As with many relationships in nature, nectar robbing offers benefits as well as potential problems. According to the University of California Berkeley's Urban Bee Gardens project, nectar-robbing behavior may actually increase genetic diversity because non-robbing pollinating species may have to visit more flowers to obtain the nectar they need, which causes the pollination of more flowers. The "Oecologia" study found that nectar robbers actually pollinated the plants about 10 percent of the time. This indicates a mutually beneficial relationship between the plants and nectar-robbing species.