Bees and butterflies help produce our food by pollinating the crops farmers grow. In fact, 35% of the world's food crops , including fruits, vegetables, nuts and seeds, depend on pollinators.
But agricultural land is a poor substitute for wild habitat — it often lacks the food and shelter that insect pollinators require. To stay healthy, these creatures need access to pockets of more natural land amid all the agriculture. Currently, pollinators around the world and in Washington are in decline , in part because of the loss of their wild habitat.
In a new study, a team of scientists from around the world analyzed a massive dataset of more than 178,000 individual insect pollinators from 19 countries to determine the minimum natural habitat on agricultural land that will allow insect pollinators — including bumble bees, solitary bees, hoverflies and butterflies — to thrive. The results varied between species, from hoverflies needing habitats with at least 6% natural features to butterflies needing at least 37% natural features in their habitats.
The researchers published their findings Sept. 25 in Science.
University of Washington News reached out to co-author Berry Brosi , UW professor of biology, to learn more about these results and how habitat is important to two types of bees native to Washington.
This paper looks at both habitat "quantity" and habitat "quality." Why is it important to think about both?
Berry Brosi: When we discuss "natural" habitat in agricultural landscapes, we're often talking about elements such as semi-wild field margins, small patches of forest or hedgerows between crop fields.
On the quantity side, having more of those kinds of elements tends to benefit many different creatures, including pollinators. But on the quality side, there is a big difference between, say, a field margin planted with a diverse set of flowers that bloom throughout the year that pollinators could visit and benefit from versus a field margin that is mostly non-flowering grasses with only one or two flowering plant species.
The timing of when floral resources are available for pollinators is especially important in agricultural landscapes, because often crop fields are "monocultures" — planted with a single crop species. Even if that crop blooms and provides a lot of resources to pollinators, typically it will only be in bloom for a couple of weeks a year, and that usually isn't enough to sustain a diverse and abundant set of pollinator species year-round.
How did the research team study habitat quantity and quality?
BB: We analyzed 59 datasets — including one from Costa Rica with data from my doctoral and post-doctoral work — to determine how much natural habitat is enough and how good that habitat needs to be to support pollinator species over the long run.
We found that there are indeed minimum habitat requirements for pollinators, and that these requirements are mostly higher than the targets currently being used by several governments and intergovernmental groups, including the European Union, which has a target of 10% natural habitat on agricultural land by 2030 .
How do these findings affect policies in the U.S.?
BB: We don't have specific targets here in the U.S., but this research can still inform how we work to conserve our critical pollinator populations in the U.S. and in Washington. For example, the U.S. Department of Agriculture has the Conservation Reserve Program that pays farmers to take some of their land out of crop production. It's been around for decades and was initially used to help prevent erosion. It often makes sense for farmers to stop planting some of their least-productive lands — which they aren't getting great yields from anyway — and to instead take a payment to manage those in alternative ways. Relatively recently, the USDA added a provision to this program to pay farmers to put in pollinator habitat. Our research findings bolster the support for doing that, and for doing more of it.
This USDA program has a close family element for me. My brother and his family have a pear orchard in Leavenworth and a smaller farm they live on in Cashmere. They would love to enroll in the pollinator program, but it's oversubscribed in Chelan County. More resources for this program would help pollinators while also helping farmers — it's a win-win.
Speaking of Washington agriculture, how do these results affect policies here in our state?
BB: Our results also underscore the positive work that the Washington legislature is doing to support pollinators. We have state laws in Washington that are focused on reducing pesticide risks to pollinators. Another state law requires that 25% of the landscaping area of any public works project be made into pollinator habitat. While state-funded public works projects don't cover a lot of area, that is a great start and well within the minimum habitat amounts we published in our analysis.
Can you give an example of an important insect pollinator here in Washington?
BB: One example is the alkali bee (Nomia melanderi), which is native to a range of dry areas in the western U.S., including much of central and eastern Washington. This bee is important for alfalfa seed farmers, who grow alfalfa to harvest seed to sell to other alfalfa growers. There are several regions in eastern Washington where growers specialize in alfalfa seed production.
For many crops in our state, growers will bring in honey bees just for the time that their crop is in bloom to pollinate them. That doesn't work well for alfalfa, because honey bees are very inefficient pollinators for its specialized blooms. Instead, some alfalfa seed producers rely on the alkali bee to pollinate their alfalfa plants, and this helps produce a good seed crop.
What kind of habitat does the alkali bee need to thrive?
BB: This species has very specific nesting requirements. For their nests to be successful, these bees need soil that has a high salt content. Farmers who use them set aside dedicated nesting habitat on their farms — essentially patches of salty mud — that they have developed specific ways of managing to make sure the bees are thriving. For example, many of these nesting habitat patches are carefully irrigated to achieve the ideal soil moisture for the bee nests. Some of these nesting patches have been continuously managed for 50 or more years. There is one large nesting patch of about 5 acres in southeastern Washington that was estimated to contain 5.3 million nesting female bees!
This paper also found that bumble bees need at least 18% natural habitat to thrive. How important are bumble bees to Washington agriculture?
BB: There are 13 bumble bee species native to Washington, and many of them are important agricultural pollinators. Unlike most insects, these bees can actually regulate their body temperature to some degree, and that means they can fly when it's too cold for many other pollinators. That makes them excellent pollinators of crops that bloom early in the season when it's still relatively chilly.
These bees can also conduct a behavior called "buzz pollinating" where they'll grasp a flower, vibrate their wing muscles — making a loud buzzing sound in the process — and shake the pollen off of flowers. That behavior makes them excellent pollinators of tomatoes in particular.
Like many other pollinators, bumble bees couldn't survive in the long run if they were placed in the middle of a tomato field. They need access to a wide range of different flowers to provide different nutrients for their diet, and access to flowers that bloom at different times in the year. Thus, it's important to have native habitat around any crop fields that bumble bees are pollinating.
Brosi's work on this project was funded by the Anne M. and Robert T. Bass Stanford Graduate Fellowship in Science and Engineering, the Koret Foundation, the Moore Family Foundation, Stanford University Field Studies and Human Biology Research Experiences for Undergraduates Programs, the Teresa Heinz Scholarship for Environmental Research and the Winslow Foundation. A full list of co-authors and funding is included with the paper .
