Pollen counts

As most people know, populations of wild bees—crucial to agriculture for their role in crop pollination—are dropping around the country. Meanwhile, the demand for insect-pollination services is increasing, according to a paper published this month in the journal Proceedings of the National Academy of Sciences.

To combat this trend, which eventually could compromise the United States’ food supply, UC Davis scientists are working with farmers throughout the Central Valley to restore native plant habitats adjacent to cropland. Their hope is that this will prompt a resurgence in numbers of wild bees, on which many farmers rely for pollination services.

Neal Williams, an associate professor of entomology at UC Davis and a co-author of the new paper, says he and colleagues have been planting native, drought-tolerant plants at 17 farm sites between Chico and Lost Hills, near Bakersfield.

The hope, he said, is to build up wild bee numbers and reduce farmers’ dependence on domesticated honeybees, populations of which have been struggling for years around the world.

Bees are a linchpin of the world’s agricultural economy. In California, crops like blueberries, squash, apples and avocados may not bear fruit if insects do not frequent the orchards and fields during bloom time and transfer flower pollen from one plant to the next.

In the case of almonds, the need for pollination is so huge that millions of hives of domesticated honeybees—distinct from the scores of native bee species that also live in North America—are shipped in from around the country and placed in the vast orchards of the San Joaquin and Sacramento valleys during the winter bloom.

Williams says the idea of his work is not necessarily to replace domesticated honeybees with wild bees as pollinators.

“No big grower would rely exclusively on wild bee populations, since there just aren’t enough,” he said.

Having wild bees in proximity to almond groves helps farmers in several ways. For one, the insects assist directly with pollination, meaning farmers may need to rent fewer beehives.

The presence of wild bees also seems to cause honeybees to work more efficiently. Williams explains that almond orchards are often planted with two tree varieties, alternating from row to row—an arrangement critical for cross-pollination between the varieties. However, honeybees often prefer to move along a single row of trees, since that way they remain in a continuous canopy of food and shelter, he explained. This is a behavior pattern not favorable to farmers.

However, Williams’ research has shown that honeybees, when in the presence of foraging wild bees, tend to cross the rows of trees more frequently, increasing the efficiency of their pollination services by about 20 percent.

The sites on which Williams is working amount to just a handful of acres so far. His goal, though, is to show farmers everywhere the potential benefits of planting and maintaining bee-friendly habitat adjacent to or within their cropland.

The paper was led by scientists at the University of Vermont and mapped the widespread decline of wild bees. The research found that wild bee abundance dropped in 23 percent of the nation from 2008 to 2013. The study also observed that 39 percent of American cropland that depends on insect pollination faces a “mismatch” between increasing pollination demands and declining bee numbers.

“Our hope is that wild bees can help offset drops in honeybee numbers,” Williams said. “But if we lose the habitat wild bees need, we can’t bring them back.”