UNIVERSITY PARK, PA — A ground-nesting bee family—commonly known as miner bees—could play a heightened role in rebuilding black cherry populations in Pennsylvania and beyond, according to Penn State entomologists who investigated the problems with the trees.

Pennsylvania’s black cherry trees are among the finest in the country, noted former graduate student Rachel McLaughlin, who led the study under the direction of Kelli Hoover and Christina Grozinger, professors of entomology in the College of Agricultural Sciences.

“Black cherry historically has been one of the more premier commercial hardwoods,” said McLaughlin, who earned her master’s degree in entomology in 2021. “It is used to make high-quality furniture, cabinets, paneling, flooring, musical instruments and more. And nearly 30 percent of the nation’s black cherry volume is in Pennsylvania.”

But fewer seedlings and saplings have been reported growing in the last 20 years. McLaughlin pointed to statistics from the U.S. Department of Agriculture Forest Service that show a 60 percent decline in established black cherry seedling densities across the entire Allegheny Plateau.

Changing weather, soilborne pathogens and insect pests are likely contributing to the decline. Given that black cherry is

insect-pollinated and unable to produce viable seed from self-pollination, a reduction in seed crops could be due to a pollination deficit, she said.

So identifying the pollinators and organizing more of them is critical. 

The team conducted a two-year study in developed, semi-developed and forested areas in Centre County and in the Allegheny National Forest near Kane. 

While flies, beetles and halictid bees—also called sweat bees—were frequent visitors to black cherry flowers during the study, the team discovered that the most important pollinator across the various landscapes was the andrenid—or miner bee—a solitary, ground-nesting bee.

The researchers, who recently reported their results in Environmental Entomology, found that miner bees represented 24 percent of all interactions with black cherry flowers and carried an average of 347 times more black cherry pollen than flies and 18 times more than halictid bees, thereby improving cross-pollination of other black cherry trees.

“Pennsylvania is home to more than 400 species of bees, but most people are familiar with only a small number of them,” said Grozinger. “Andrenid bees are very important for springtime pollination of flowering trees, including apples.

“Most people understand that pollinators are essential for the production of food crops,” she said.

Hoover encouraged land managers to take steps to attract and support miner bees through practices such as thinning or clearing trees at high density from sunny, well-drained areas.