The common garden tomato presents an interesting case study in plant reproduction. While many assume the honey bee is the primary pollinator for all crops, the tomato plant has a different requirement. Tomato flowers are classified as “perfect,” possessing both male and female reproductive structures within the same bloom. Although technically self-pollinating, successful fruit development requires a physical movement or vibration to release and transfer the pollen. Certain species of bees are uniquely equipped to provide this necessary mechanical assistance.
How Tomato Flowers Achieve Pollination
The biology of the tomato flower dictates a need for mechanical help to achieve fertilization. Each flower contains the male pollen-producing anthers and the female pollen-receiving stigma. The anthers are highly specialized, forming a fused cone-like tube that tightly encloses the pollen.
This design means the pollen is not easily exposed for transfer by simple wind currents. Instead of opening up like a typical flower, the anther cone releases its pollen through small pores at the tip. To force the pollen out, the flower must be vibrated at a specific frequency.
This necessary shaking action is known scientifically as sonication, or more commonly, “buzz pollination.” Without this intense vibration, the pollen remains trapped, and the flower will drop off without producing fruit. While wind can occasionally trigger some pollen release, a more vigorous and sustained vibration is required for optimal fruit set and size.
The need for this highly specific mechanical trigger explains why casual visits from many common insects are insufficient. The method of pollen release is a biological adaptation that limits the number of species that can effectively pollinate the tomato. The result of effective buzz pollination is a significantly higher fruit set and heavier fruit weight compared to wind-only pollination.
The Specific Role of Bumblebees
Bumblebees, belonging to the genus Bombus, are particularly adept at performing the buzz pollination required by tomato plants. Unlike many other insects, a bumblebee can physically grasp the flower and decouple its flight muscles from its wings. It then vibrates its thorax at a high frequency, often around 400 Hertz, which is the precise action needed to shake the pollen from the flower’s poricidal anthers. This specialized technique is what makes the bumblebee an unparalleled pollinator for tomatoes.
Honey bees (Apis mellifera), despite their reputation as generalist pollinators, cannot perform this sonication behavior. The anatomy and muscle control of the honey bee do not allow it to vibrate the flower with the necessary intensity and frequency.
Tomato flowers do not produce the sugary nectar reward that honey bees seek for making honey. Since the only reward is pollen, which is difficult for a honey bee to extract, honey bees will bypass tomato flowers entirely if other nectar sources are available. This physiological and behavioral difference means that bumblebees are the only highly effective insect pollinators for this crop. A single visit by a bumblebee is often sufficient to ensure successful fertilization of a tomato flower, which is an efficiency that commercial growers rely upon.
Ensuring Successful Pollination in Gardens and Greenhouses
For commercial growers, especially those cultivating tomatoes in controlled environments like greenhouses, the pollination process is carefully managed. Growers often introduce commercially raised colonies of bumblebees, placing them in densities that can range from seven to fifteen colonies per hectare for large-scale operations.
The home gardener or small-scale grower, however, can easily mimic this natural buzz pollination using simple manual techniques. Gently shaking the entire plant or the individual flower cluster every two to three days during the bloom period can replicate the effect of wind or a bee’s visit. A highly effective method is to use a battery-operated electric toothbrush, which simulates the high-frequency vibration of a bumblebee. By placing the vibrating head of the toothbrush against the stem just behind the flower for a second or two, the pollen is effectively dislodged and transferred.
Environmental control is also a factor, as pollen transfer is most successful when daytime temperatures are between 70 and 85 degrees Fahrenheit (21 and 29 degrees Celsius). Maintaining a relative humidity between 50 and 80 percent is also important. Excessively high humidity can make the pollen too sticky to move, while very low humidity can cause it to lose viability.