Seeking pollinators in wings

On a sunny morning, amid 35 acres of Montgomery County farmland lush with tomato, bean, basil and cantaloupe, Neal Williams affixes a yellow flower to a stick and steps gingerly through the watermelon vines, intent on catching a bee.

The flower hasn't been pollinated yet - it's been covered since dawn by a cap of bridal veil - and he wants to find out how much a single bee will deposit on its first visit.

This will help Williams determine how bees pollinate crops, how good a job different species do, and ultimately, how to ensure the security of the nation's fruits and vegetables.

Today, when most crops are pollinated by an import - the European honeybee, brought here in the 1600s to sweeten the colonial diet and now in mysterious decline - he wants to find out whether native bees could, if need be, take up the slack.

"This is about figuring how to make sure we have a sustainable and stable pollination of our food supply," says Williams, a Bryn Mawr College biologist who kept honeybees as a youth in Wisconsin and has studied native bees throughout the region, from the center of Philadelphia to suburban parklands.

Oddly enough, it took a crisis in a nonnative species to prompt a closer look at the country's native species.

At the American dinner table, about one bite in three depends on bees. Flying from flower to flower, they're just looking for food for their young. In the process, however, bees pollinate the flowers.

Domesticated honeybees have become a cornerstone of American agriculture - more than 90 crops depend on them - because they're so easy to manage.

Their boxlike hives can easily be transported long distances and deposited throughout the vast, single-crop fields that are the backbone of corporate agriculture. And they can be brought in on a precise timetable, before or after the spraying of insecticide.

A 2006 National Research Council report warned that population trends for the nation's pollinators - not just bees but also butterflies, moths, bats and birds - were "demonstrably downward." Habitat loss is a major factor.

Honeybees have been beset by mites and viruses for years, but within a month after the report's release, a new problem arose that was all but catastrophic.

A Pennsylvania beekeeper opened his hives, already positioned in Florida orange groves, and discovered that the bees were gone, presumably dead.

That year, the nation's beekeepers lost nearly a third of their hives, much of it in ghostly disappearances that are a hallmark of what is now known as colony collapse disorder. Only by dint of good weather and intense bee management were Jersey blueberries, Pennsylvania pumpkins, New York apples and California almonds successfully pollinated.

Last winter, beekeepers lost even more. The price of hives rented to farmers has nearly doubled in just over a year, said Dennis vanEngelsdorp, Pennsylvania's acting apiarist.

Despite intense study, much of it led by Pennsylvania State University, the cause of the die-off remains unknown.

So people are suddenly paying attention to native bees.

The farm bill enacted in May includes funding for bee studies. Conservation groups are beginning to factor bee needs into their planting strategies.

And research into native bees is finally on the radar.

Oddly enough, while everyone agrees that without pollinators, entire plant systems would collapse, followed by a cascade effect among species that evolved with them, scientists still don't have a good handle on the native bee populations.

Compared to, say, birds, "we know next to nothing about bees," says Sam Droege, a biologist at the U.S. Geological Survey's Patuxent Wildlife Research Center in Laurel, Md., who analyzes changes in plants and animals.

Indeed, scientists preparing the first global checklist of bee species in more than a century, released last month, discovered there were a good deal more bee species than previously believed - nearly 20,000, more than all birds and mammals combined.

Pennsylvania has begun its own statewide survey. Taxonomist Rick Donnovall has been scrutinizing collections maintained by the state Department of Agriculture and various museums, recording which bees have been found when and where in the past. He also has a network of collectors trying to determine what's out there now.

The Philadelphia region may have as many as 350 species of native bee. Some are as small as a gnat, others as large as the familiar bumblebee, with colors ranging from dark brown or black to metallic green or blue. Many are striped.

Their common names often reflect how they nest: Mason bees use mud to seal nests in rotting wood. Carpenter bees chew tunnels in wood. Digger bees burrow into the soil.

No one thinks the country will ever be able to produce enough food without domesticated honeybees. Williams, an ecologist and professor of biology at Bryn Mawr, has studied bees on California farms - industrial operations sprawling over hundreds of acres per field - and found that the valuable native pollinators were long gone.

Closer to home, Williams and his collaborators, including Rutgers evolutionary biologist Rachael Winfree, formerly at Princeton, have been looking at 23 farms in central New Jersey and Southeastern Pennsylvania that typically are a far smaller 25 acres.

And while they are located in a highly developed region - one is bisected by the Pennsylvania Turnpike and abuts Plymouth Meeting Mall - patches of natural habitat remain.

The researchers logged visits to 15,888 watermelon flowers by 46 species of native bees. On farms where honeybees were present as well, the natives were more effective pollinators, depositing more pollen per visit.

A recent study published in the journal Ecology Letters concluded that native bees alone provided sufficient pollination at 90 percent of the farms.

Droege, the Patuxent researcher, says that finding is significant: "You have to have enough native habitat left to 'stockpile' native bees."

Now, Williams and his students are delving deeper into the farmscapes.

They're looking at which native plants, including weeds, help support populations of native bees. If some species are lost, they want to know if others can fill the gap.

Last week, three students pulled into Barry Davis' farm fields south of Collegeville at dawn, a moment of growing light and birdsong when the watermelon flowers were just opening.

Each flower stays open for a single day, and because the blossoms are either male or female, they can't pollinate themselves. They need bees.

The researchers tracked which bees went where, and how often. (Happily for them, most native bees rarely sting.) They collected flower specimens, as well.

Back in the lab, they smeared the pollen on a slide to count each grain under a microscope. This would show them which bees were doing the better job.

Watermelon flowers need 1,000 to 1,500 grains of pollen to produce a marketable fruit. The best bees - bumblebees, it turns out - typically deposit 150 grains on each visit.

Davis has been trying to encourage the native population by maintaining hedgerows at the edges of fields and letting swaths of weeds grow between some of the rows of crops.

"I try to keep it wild, as far as allowing nature to be part of what's there," says Davis, who sells his produce at a fieldside farmstand on Smith Road.

Crops are intermittent. But here, the flowers of shepherd's purse, cocklebur and fleabane will provide a backdrop of nutrition.

Williams believes that just as farmers have adopted integrated pest-management programs, they also would benefit from integrated pollination strategies.

As the sun rose higher, the day warmed and Williams pitched in to help his students finish.

The next day, and every other sunny day through early August, their study of the delicate interplay between bee and banquet - theirs and ours - would continue.

An estimated 4,000 bee species are native to the United States, including about 350 in the Philadelphia region.

Some of the locals considered important for agriculture:

Common bumblebee: Bombus impatiens is a generalist. It lives in farmed areas, suburbs and cities. It nests in cavities, including former mouse nests.

Sweat bee: Augochlora pura is important for melons and tomatoes.

A distinctive metallic green, it burrows in wood to nest.

Squash bee: Peponapis pruinosa, a ground nester, forages early in morning. It pollinates squash, melon, zucchini and related gourdlike vegetables.

Mason bee: Species in the Osmia genus pollinate spring orchards.

Dwarf carpenter bee: Members of the Ceratina genus are important for berries and watermelon. They nest in the centers of dead raspberry and elderberry stems.

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