Defenders Magazine

The Buzz About Bees

Native bees are small and unfamiliar - but they're crucial for keeping food on your table.

By Cynthia Berger

© Dwight Kuhn

A huge dinosaur skeleton stands in the lobby of Princeton University's Guyot Hall, but Rachael Winfree wants to show me something much smaller. It's a warm July morning and we're in a second-floor lab that smells faintly of mothballs. Winfree, a post-doctoral researcher, bustles to a cabinet, pulls out a glass-topped metal drawer and sets it on a table.

Inside are insect specimens mounted on slender pins: umblebees big as thimbles…metallic-blue orchard bees, the size of houseflies…tiny black sweat bees. "And these really beautiful green ones," Winfree says, "that's also a kind of sweat bee." We're looking at just a few of the approximately 4,000 species of wild bees native to North America.

Winfree and University of California-Berkeley professor Claire Kremen are studying the role these wild bees play in pollinating cultivated crops. It's a subject of more than academic interest. "Eighty percent of the world's crops and one-third of the United States' agricultural output depend on pollinators whose populations are in jeopardy," says Gabriela Chavarria, vice president for conservation policy at Defenders of Wildlife. Without bees, there would be no apples, no squashes, no sunflower seeds or alfalfa, fewer almonds, sweet cherries, blueberries, cranberries and strawberries. Tomatoes would be smaller and less tasty.

As bees buzz along from flower to flower, collecting pollen to feed their young, some of the pollen—from the male flower parts—brushes off on female flower parts, ensuring fertilization and the production of seeds and fruit. Right now, most North American farmers growing bee-pollinated crops rely not on the native bees in Winfree's tray, but on the European honey bee, first brought to North America in the early 1600s by English and Dutch settlers as well as Spanish priests traveling to Mexico and what is now the American Southwest.

Today, honey bees are big business in American farming. About 150,000 beekeepers own about 3 million hives; many fulltime beekeepers are migratory, renting out their bees to farmers and trucking their hives from crop to crop. Honey bees add an estimated $15 billion in value to American agriculture each year. But honey bees are in trouble. Continued insecticide use and two types of deadly mites have cut honey bee populations in North America dramatically: the domesticated population is half what it was in the 1950s, and the number of wild honey bees may be down 90 percent.

So far, the honey bee shortage has not caused crop failures, but Kremen says there are some warning signs. In February 2005, for example, California almond growers couldn't get their hands on enough bees to pollinate the entire crop. "Some farmers failed to meet expected yields as a result," despite importing bees from as far away as Australia, she says.

Could wild bees do the job instead? Some farmers are already trying them out—for example, the blue orchard bee, which, as the name suggests, pollinates orchard trees. This species is hardier than the honey bee; it's happy to fly in cloudy and cool conditions, when honey bees just hunker in their hives. It's also hardworking; studies show 250 to 300 female blue orchard bees will pollinate an entire acre of apples or almonds—work that would require 20,000 to 60,000 honey bees.

Like most native bees, blue orchard bees do not form hives the way honey bees do. Each female has her own nest site—a hollow plant stem or an empty tunnel left by a wood-boring beetle—and lays just a few eggs. So, instead of bringing in a hive to get an orchard pollinated, farmers must work to increase local wild bee populations by providing artificial nests—typically, wooden blocks drilled with holes of a suitable size.

Another crop where wild bees are already hard at work is seed alfalfa. U.S. farmers have long relied on the alfalfa leaf-cutting bee, a naturalized species from Eurasia, to pollinate this crop. But U.S. farmers don't cultivate sustainable populations; instead, replacement bees are constantly imported from Canada. "Leaf-cutting bees have gotten expensive, so all of a sudden, another species, the alkali bee, looks nice," says Jim Cane, a research entomologist with the U.S. Department of Agriculture's Bee Biology and Systematics Lab in Utah.

Cane is working with farmers in Washington State to encourage alkali bees to take up residence in their fields. Females need damp soil with a salt crust to dig their underground nesting burrows. "Farmers give up one acre in every 200 to create bee nesting sites," Cane says. An irrigation system may be needed to keep the soil moist.

Kremen and Winfree are measuring how well wild bees can substitute for hired honey bees, but they're also trying to find out what kinds of conditions on and around farms will naturally support wild bees. Could simple land-management practices help wild bees to flourish? "At the end of this study," says Winfree, "we'd like to be able to tell farmers, ‘Here's things that you could do to encourage wild bees.'"

The current study involves 25 New Jersey farms growing watermelon and tomatoes. "The only way to know what proportion of the pollination is done by wild bees is to measure it in the field, so that's what we are doing," Winfree says. To see how data collection works, we hopped in her car and drove a few miles—past Princeton's stately homes, out a rural road under stately trees—to Terhune Orchards.

Terhune is a small, family-owned farm that grows a variety of crops: apples, cherries and peaches; pick-your-own blueberries and raspberries; and other fruits and vegetables. Farmers Gary and Pam Mount practice integrated pest-management, which means minimizing the use of chemical pesticides. "This farm has some of the highest wild bee diversity of any of the farms we study," says Winfree.

We walk past the farm store; past the blueberry patch covered with bird netting; and out to the watermelon patch. Winfree's field assistants, Christina Locke and Hannah Gaines, are already here, wearing sunhats and holding clipboards, collecting data to establish "flower visitation rates."

Gaines clicks her stop watch and we focus on one tiny, bright-yellow watermelon flower. One of the metallic-green sweat bees flies in. "That's a female flower, so pollination is occurring!" Winfree exclaims. A small black sweat bee follows, then a honey bee—probably from a managed hive nearby, says Winfree. The Mounts do bring domestic honey bees in to pollinate some crops, but no hives are here now.

The researchers are also doing a wild plant census on each farm, to find out what flowering "weeds" are present. "Weeds may be a good thing for bees," Winfree says. "A crop plant puts out a lot of blooms, but just for a short time. Then they are gone. Wildflowers may tide the bees over until the next crop plant blooms."

The study is ongoing, but preliminary results are intriguing. "In a pilot study in 2004 we found that watermelon got about equal numbers of visits from wild bees and honey bees, which is astonishing," Winfree says. "The farmers are paying for honey bees to pollinate their melons, and yet some of the farms we looked at seem to be getting the same service from wild bees—for free."

Cane cautions that wild bees most likely will never provide all the pollination services needed on large farms growing a single crop. "You need enough pollinators to make sure every single flower gets visited," he says. "That means a crop like cranberry, with 20 million flowers per acre, would need more than a thousand wild bees per acre," an impossibly large population. "Seed alfalfa in southeast Washington State has more than 400 million flowers per acre," he continues, "and fields can be 450 acres apiece—and all the bloom happens in a two-week period. You do the math."

Winfree admits one reason wild bees seem to be so successful in this area is that small farms are nestled within habitat that provides nest sites for wild bees. "There's a lot of suburbia in this part of the world," says Winfree. "It shows up on [maps] as residential land—which is not what we classify as wild habitat. But yards with big trees and natural landscaping can still provide nest sites for bees," which can then go to work on neighboring farms.

Even as research proceeds, the buzz on wild bees is promising enough that a pilot program in Montana under the Department of Agriculture's Natural Resources Conservation Program offers incentives to landowners who help native pollinators by cultivating a constant bloom of wildflowers on their land. "We're hoping this program will expand to other states," says Chavarria. "It's the new wave in conservation. We know it's not enough just to protect a species—at the end of the day, that species needs habitat."

Before we leave Terhune Orchards, Rachael Winfree takes me to see a plot of cherry tomatoes. "This crop has no nectar, so the honey bees don't come to it at all," she notes. And farmers don't worry about that, because a cherry tomato can self-pollinate—it doesn't absolutely need bees. But Kremen's lab has shown that when wild bees do visit, cherry tomato sets more fruit…and bigger fruit. "In a way it's less exciting for us to collect data on tomatoes because you see fewer bees," Winfree says, "but on the other hand, the bees you do see—they're all wild."

Cynthia Berger is the author of Wild Guide: Dragonflies and Wild Guide: Owls. A public radio producer, she lives in central Pennsylvania.