On the buds and the bees

Carl Sagan once wrote, “If you wish to make an apple pie from scratch, you must first invent the universe.”

By all rights, that invented universe would include the 20,000 or more acres of apple orchards now in bloom in Adams County, the heart of Pennsylvania’s Fruit Belt. Biglerville is the epicenter of the county’s apple growing activity and home to Penn State’s Fruit Research and Extension Center. 

Blooming apple trees in the Penn State research orchards in Biglerville, PA
Blooming apple trees in the Penn State research orchards in Biglerville, PA Image: M. Beattie-Moss

If you wish to invent a universe that will give rise to apple pies, you might also need some researchers to teach you a thing or two, and luckily the Center has some good ones. On a recent visit, I spent time in the orchards with Dave Biddinger, fruit tree research entomologist, and Ed Rajotte, professor of entomology and integrated pest management, and I learned some new things about the buds and the bees. 

While the public has absorbed the basic message that bees are important pollinators, many of us still can’t really picture how the process works — and why there’s no apple pie without it.

Before there is pie, there is sex. Whether we’re talking about reproduction or baking, a lot depends on timing and favorable conditions. Each blossom on the tree contains sexual organs. The act of pollination involves each pollen grain — a tough-walled capsule containing male reproductive cells — being transported, usually by an insect or bird, to the female reproductive part of the flower called the pistil. At the base of the pistil are the ovaries housing the tree’s egg cells; this part of the story should be sounding familiar to anyone who took a high school sex ed or bio class.

An apple tree in bloom at the Penn State Fruit Research and Extension Center
An apple tree in bloom at the Penn State Fruit Research and Extension Center. Image: M. Beattie-Moss

Apple trees can’t run around the orchard speed-dating other trees, but they do need to “play the field” rather than just settle for the girl or boy next door — after all, they’re cross-pollinators, which means they need pollen from a variety of types or “cultivars” of apple trees in order to bear fruit. (Yes, some types of fruit trees are self-pollinating; we won’t try to extend the metaphor to cover this fact.) For this reason, an apple orchard always has different varieties of commercially popular apples planted in close proximity to each other, as well as crabapples, heavy bloomers with abundant pollen.

Photo by M. Beattie-Moss
Hornfaced bee foraging on apple blossom

Bees are the pollinators that broker the “romance” between trees across an orchard. They’re in it for the protein and sugar-rich pollen and nectar found in each blossom. As they move from tree to tree foraging for food, they also shake off the pollen on their bodies into the waiting flowers. Every pollinator species — bats, hummingbirds, butterflies, flies, moths, beetles, and a wide variety of bees — evolved to have a preference for particular plants and food. Part of the reason bees are so important in an orchard is they eat pollen in addition to nectar. By contrast, bats, hummingbirds, and butterflies are primarily interested in nectar. So, in the apple-pie universe we’re inventing, we’re definitely going to need bees.

Bee boxes in the orchard during pollination season, Biglerville, PA
Bee boxes in the orchard during pollination season, Biglerville, Pa. Image: M. Beattie-Moss

But let’s get back to timing. Every part of this process has its lifespan: the apple tree is productive for 20 to 30 years; some types of bees (let’s use the blue orchard and hornfaced bees as examples here) live 4 to 8 weeks; and the flowers last about 2 weeks.

In the world of orchard growing, this means there’s a small window of opportunity each spring for trees to date, mate, and “set seed” which is the moment in the flower’s life when the male and female reproduction cells meet, fuse and start growing a fruit.

When we see fruit trees in bloom, we think “Ah, it’s spring!” When orchard growers see this sight, they see the “make or break” season of their growing year in terms of production and profits. A shortage of pollen in the field will produce a shortage of apples at harvest, explains Biddinger. To ensure that as many flowers set seed as possible, growers do all they can throughout the year — including introducing and managing pollinators, pruning, grafting, pest control, irrigation, using wind machines to prevent frost, and more — to increase the chance for success during apple blossom time.

To the grower and to us — the would-be bakers of apple pie — this whole enterprise is about the apples. To the tree, it’s all about the seeds. After the flower is set through pollination, its ovary swells and creates layers of sugary juicy flesh to encase and nourish the seeds, which are the tree’s offspring and ensure the continuation of apple trees in this world.

Want to check the next apple you eat to see how successful its pollination was? Just count the seeds. A fully pollinated apple will have ten seeds, two in each of the five seed pockets in the core.

In fact, now that we’ve successfully invented the necessary universe, you can do this seed-counting experiment while you bake your apple pies from scratch.

Members of the news media interested in learning more about the Biglerville Fruit Research and Extension Center may contact Melissa Beattie Moss at mbmoss@psu.edu.

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