Efforts to help pollinators show successes, limits

Though not quite the bee’s knees, a three-year attempt to conserve bee populations by introducing pollinator habitats in agricultural areas of North Carolina showed some positive effects as bee abundance and diversity increased in the areas studied.

However, results from a study examining the effectiveness of the program also showed that habitat quality played a key role in these positive effects and that habitat quality could be influenced by the way areas are managed over time become.

Researchers from North Carolina State University studied the effects of a US Department of Agriculture program that installed pollinator-friendly flowers at 16 agricultural research stations from the mountains to the coast from 2016 to 2018. Mixtures of planted bee-friendly flowers have been studied for their effectiveness in supporting bee populations – with the aim of increasing bee abundance and diversity.

The research is published in the journal Frontiers in ecology and evolution.

Honey bee specialist David Tarpy, a professor of entomology at NC State and co-author of an article describing the research, recalled thinking the program was a unique opportunity to examine government-led conservation efforts. “We should get in on the ground floor and measure this and see if it works from day 0, not after the fact,” he recalls.

“We didn’t want to let this ‘natural laboratory’ opportunity slip by without actually recording the data,” added Hannah Levenson, a postdoctoral fellow at NC State and corresponding author of the article.

The researchers visited all 16 sites four times a year and caught bees in nets and in cups – called beehives – that were painted to mimic the UV reflections of flowers. In total, the researchers collected more than 16,000 bees from 128 different bee species.

The results showed that bee abundance has increased over time, with more bees collected in 2018 than in 2016. Meanwhile, biodiversity increased in 2017 and declined slightly in 2018, although both years showed a large improvement from 2016.

“We were very pleased to see that the number and number of bee species found has increased over time,” Levenson said. “It was also exciting to see how many species we have documented, particularly for studying one type of habitat. This study was limited to agricultural land, but we still found nearly 130 species of bees.”

However, the study also showed that flower quality was a key factor in bee abundance and diversity, with areas with higher flower quality attracting more bees and more bee species. Poorly maintained areas with degraded flowers, weeds and grasses were left behind for bee collection.

“There are 564 bee species in North Carolina, and they have very different life cycles,” Levenson said. “Some are active in early spring when the flowers are just beginning to sprout. Other species are active in summer. At the end of summer, most bee species are active but have the fewest resources available—this is called a shortage. Develop seed mixes that bloom every season so we can support as many North Carolina bees as possible.”

Levenson said there were some surprising results, including some bee species appearing in unexpected areas.

“We found some specialized bees in places you wouldn’t expect,” Levenson said. “There were no squash plants in our plots, but we found squash bees. It is encouraging that these planted habitats can provide some level of support to specialized species like this, which are economically important pollinators.

“We also found one particular bumblebee – Bombus pensylvanicus – which is currently under review for possible inclusion on the endangered species list,” she added. “We’ve found large numbers of them, so it’s possible they’re attracted to agricultural areas more than other areas. We have submitted the data to Fish and Wildlife so that it can be used to decide whether or not it should be listed as endangered.”

Levenson said the program, which is studying the impact of adding large-scale pollinator habitats, is forward-looking.

“I want to give credit to the NCDA. To our knowledge, they were the first government organization to conduct such test plots, and hopefully our findings could encourage more government programs to take action to protect the environment,” she said. “Even if the habitats weren’t perfect, they still made a difference.”

Researchers hope that more studies like this can be conducted in different types of habitats, such as forests or urban areas, to get a broader picture of North Carolina bee populations.

“Regardless of the landscape, we’ve shown that maintenance and monitoring are important to efforts like this,” Tarpy said.