Buzzing Bees in the School Hoop House

Why the Tomatoes Did Not Set

1The garden club at Cedar Hill Middle School grows tomatoes and strawberries in a hoop house, a long tunnel of clear plastic that keeps plants warm in early spring. Last year the tomato plants were covered in yellow flowers, but only a few of the flowers turned into tomatoes. Garden teacher Rosalind Achebe asked the club, including sixth grader Tomasz Ilunga, to find out why. With the plastic sides closed, there is almost no wind inside, and few insects find their way in.

2A tomato flower has yellow petals that bend back. In the middle, its anthers are joined into a narrow cone wrapped around the pistil. The pollen is held inside the cone and comes out through thin slits when the flower is shaken. A bumblebee grabs the cone with its jaws and vibrates its flight muscles very fast without flapping its wings. This makes a loud buzz and shakes pollen out onto the bee's body and onto the tip of the pistil. Honeybees do not buzz flowers this way. A bumblebee's grip leaves a small brown mark on the cone, so growers can tell which flowers it visited.

3This spring the club planted three rows of the same tomato variety, from one seed packet, in the same soil and gave every row the same water. In Row 1, no one touched the flowers and no bees were added. In Row 2, each morning a club member held a buzzing electric toothbrush against each open flower cluster for about a second. Row 3 was closed off with netting, and a box of bumblebees from a garden supplier was set inside it. In each row, the club tagged 60 flowers, checked them for brown marks and counted how many grew into tomatoes.

4Strawberry flowers are built differently. Each one has dozens of tiny pistils packed on a mound in its center. Each pistil that gets pollen grows into one of the small seeds on the outside of the berry, and the red flesh swells around the seeds that formed. The club watched tagged strawberry flowers in short visits each day and counted how many times bees landed on each one. Later they weighed the berries.