What you can do to ensure they’re here to stay

A bumblebee, Bombus impatiens, working the apple bloom. Note the loaded pollen baskets, or corbicula, on its hind legs.
Photo courtesy of Koppert Biological Systems.

For decades, native pollinators have been the redheaded stepchildren of agriculture, largely ignored and overshadowed by European honeybees. Nevertheless, attitudes are changing as more light is shed on them and their role in the agricultural landscape. The overwhelming consensus stands firm: if we do what we can to support native pollinator populations, we’ll not only be doing them a favor, we’ll be doing ourselves a favor, too.

Although it is often quoted that honeybees annually pollinate $15 billion in U.S. crops, the extent to which native pollinators contribute to this country’s fruit, vegetable and nut production has been an unknown. However, that unknown has become something worth exploring, partly because honeybee colonies have experienced a 59 percent decline over the last 60 years, and partly because many native pollinator populations are also thought to be on the decline. In 2006, John Losey, a Cornell University entomologist, and Mace Vaughan, conservation director of the Xerces Society for Invertebrate Conservation, attempted to put a dollar value on native pollinator services in the U.S., and their study came up with $3 billion annually. Meanwhile, scientists in the field have confirmed that these insects are working alongside honeybees, diligently pollinating crops produced by U.S. growers.

Diversity by design

A growing number of scientists are surveying flowering crops for native bee species and reporting some interesting, even surprising, findings. Bees are the focus of most research, and this article, because they tend to radiate from a central nest, forage within close proximity to that nest and stick to one flower type, thereby ensuring pollen is transferred within a plant species. University of California and Princeton University researchers, who have been collaborating on native bee studies for the past decade, have been assessing the role bees play in pollinating select California crops. Study results have revealed a strong native bee presence: 39 species in watermelon fields, 34 species in sunflower fields and five genera in tomato fields. Similarly, a team of Cornell entomologists surveyed 11 apple orchards in upstate New York during the May 2009 bloom. After collecting more than 3,000 specimens, a total of 81 native bee species were identified, with the number of species per orchard ranging from 15 to 42.

Basic studies such as these are revealing the presence of diverse pollinator communities, but are all bees created equal, with regard to the services they provide? The unequivocal answer is, no. Variations in body size and mouthparts indicate each species is designed to pollinate a set range of flower sizes and shapes. When behavioral differences among species are taken into consideration, the pollination puzzle’s complexity skyrockets. Yet, researchers are concluding that native bee communities can do just as good a job at pollinating a crop as managed honeybee colonies, and sometimes they can do better. Take cranberry, blueberry, tomato, eggplant and potato blossoms that are designed to be pollinated by a specific type of insect. Sonication, or buzz pollination, occurs when a visiting bee takes hold of the blossom’s anther and vibrates its wing muscles to give itself (and, incidentally, the stamen in wait below) a pollen shower. Bumblebees are famous buzz pollinators; honeybees are not. That is why growers are increasingly employing commercially produced bumblebee colonies for their fields and greenhouses. Yes, it is possible for these blossoms to produce fruit without being “buzzed,” but growers have learned the resulting yield is considerably lower, both in number of fruit and respective size.

A bumblebee, Bombus impatiens, working the apple bloom.
Photo courtesy of Koppert Biological Systems.

Supporting native bee populations

If your business is producing and selling an insect-pollinated crop, it’s likely you’re benefiting from the presence of native bee communities. It’s also likely you could further encourage and support those communities by creating and maintaining foraging and nesting habitat.

Yes, your crops are a source of nectar and pollen, but for what percentage of the growing season? Bees require food for months on end. Explore the art of strip cropping and incorporate a variety of crops into your field design, crops that both you and the pollinators can benefit from. Additionally, create natural areas near field edges, keeping in mind the closer to the field the better. The more time a bee spends flying from its nest to a foraging site, the less time it spends on nest maintenance and pollination. Those areas you create for foraging habitat should support numerous flowering plants with overlapping bloom times. Diverse and abundant plant species scattered throughout your growing landscape will ensure the presence of diverse and abundant pollinator species.

For the bees, early spring foraging opportunities are particularly important and can make the difference between a weak and strong colony. Several tree species, including maples and willows, are an early source of nectar and pollen. Black locust and black cherry trees are also beneficial species, due to prolific flowering habits. If you need to establish a windbreak, keep these species in mind.

Bees cannot subsist on foraging habitat alone, however. The presence of adequate nesting habitat is a must. Crop fields tend not to be adequate because they are so intensely managed (i.e., tilled). If you want to encourage and support native bee populations, you’ll need to provide natural, untilled areas for nesting sites. Of the more than 3,000 bee species native to this country, roughly 70 percent nest underground. For them, well-drained, south-facing slopes are ideal, particularly if large patches of exposed soil are present and vegetation is sparse. Other bee species, such as tunnel bees, nest in abandoned beetle larvae cavities in standing dead trees, old tree stumps and downed logs, or they tunnel and nest inside soft, pithy twigs of such shrubs as elderberry and Rubus spp. For this reason, try not to remove dead or dying trees and shrubs. Bumblebees nest either aboveground in tree cavities, under clumps of herbaceous vegetation, or underground in abandoned rodent burrows or tunnels. We know for a fact they use grassy strips between field crops and wooded edges. To support their populations, create grassy strips measuring at least 5 feet wide alongside your fields and only mow them every few years during late fall or winter.

It goes without saying that the use of pesticides must be carefully thought out. Either avoid their use or apply in the evening or early morning to minimize their impact on pollinators. The same goes for herbicides: target the weeds in your fields, not those alongside them.

The business of habitat

The trouble with creating habitat for pollinators is that you may be taking growing space out of commission, space that puts dollars in your wallet. However, an increased native bee presence could also be financially beneficial, if it’s eliminating the need to own or hire honeybee colonies, or if it’s significantly increasing pollination rates and fruit set. So, the natural question is: How much habitat do native pollinator populations need?

Unfortunately, there are no precise equations or ratios that tell us we need so many square feet of natural habitat for every so many square feet of cropland. It just isn’t known. The number of variables involved—crop type, native plant assemblage, pollinator biology, microclimate, surrounding land use, etc.—make the answer seem nearly unattainable. Yet, researchers are currently asking that golden question and are on the road to answering it. Meanwhile, growers are left to do the best they can with the information they have.

Pollinator resources for growers

There is a wealth of information and assistance out there for growers interested in creating and maintaining native pollinator habitat. One example is the USDA’s Natural Resources Conservation Service that, through the Conservation Stewardship Program, provides technical and financial assistance to agricultural producers interested in conserving and enhancing natural resources on their land. Native pollinator habitat falls under that umbrella. To find out if you are eligible, go to www.nrcs.usda.gov/PROGRAMS/new_csp/csp.html.

The Conservation Reserve Program, administered by the USDA’s Farm Service Agency, offers cost sharing and annual rental payments to producers interested in establishing linear buffer plantings between cropland and waterways. The primary goal is to prevent soil erosion and protect water quality, but a secondary goal can be to create pollinator habitat. For information on upcoming sign-ups and to see if you qualify, contact your local FSA office or visit www.fsa.usda.gov.

There are also a number of nonprofits concerned with native pollinator conservation. The Xerces Society (www.xerces.org) is an excellent example with a website to match. If it’s an old-fashioned book you’re craving, “The Pollinator Conservation Handbook,” produced by the Xerces Society in association with The Bee Works, should satisfy that craving. The same goes for “Managing Alternative Pollinators: A Handbook for Beekeepers, Growers, and Conservationists,” written by Eric Mader, Marla Spivak and Elaine Evans and published by Sustainable Agriculture Research and Education (www.sare.org).

It’s in all of our best interests to take steps that support native pollinator diversity and abundance. After all, it’s estimated that a third of the crops produced by U.S. farmers are done so with their help. Developing a creative strategic field design that takes into consideration not only your farm’s needs, but also the habitat requirements for native pollinators, is not just a thing of the future, it’s today.

The author, a regular contributor to Growing, is a biologist who lives and farms in Vermont’s Northeast Kingdom.