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.