The Buzz: Hemp and Bees

In 2016, a United Nations–sponsored scientific report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services concluded that about 40% of the world’s invertebrate pollinators, including bees, are facing extinction.1 Pollination is required for three-quarters of global food crops, making the possible future extinction of bee species a serious threat for agriculture and the world’s food supplies. Various bee species have since been classified as endangered in the United States and other countries. Therefore, researchers have been studying ways to boost bee populations.

What the Science Says
In February 2020, a scientific study on the potential value of Cannabis sativa for supporting bee communities was published by a group of plant and insect researchers at Cornell University: Heather Grab, PhD, a senior lecturer in hemp science at the School of Integrative Plant Science at Cornell University; Katja Poveda, PhD, an associate professor in the department of entomology at Cornell University; and Nate Flicker, an undergraduate researcher who spearheaded the project and wrote his honors thesis on hemp and bees.2 They investigated the types of bee species that visited industrial hemp crops on 11 farms in the Finger Lakes region of New York, which has a diverse array of agricultural land use as well as natural deciduous forests, woodlots, and field pastures. Industrial hemp has recently been introduced for production of grain, fiber, and CBD extract. The hemp fields in the study ranged in size from less than 0.1 acres to greater than 11 acres and included a variety of hemp cultivars.

Why the scientific interest in hemp and bees? Bees have been negatively affected by the loss of habitat, limited diversity of natural pollen/nectar sources, and use of chemical pesticides brought on by large-scale agriculture. The addition of hemp into American agriculture may provide bees with a new and much-needed source of pollen.

Hemp is a dioecious plant, meaning that there are separate male and female plants, not one plant with both male and female flowers. It’s primarily wind-pollinated and lacks the bright-colored and scented flowers with nectar that are typical of insect-pollinated plants. Male hemp plants are taller than female plants and release large amounts of pollen for several weeks in midsummer, making them attractive to bees. Female hemp flowers lack floral nectar and so are not visited by bees, the Cornell researchers explain in their study. “Hemp can be a great resource for bees because it sheds its pollen during the midsummer period when there are fewer flowering resources available for bees. Therefore, hemp might provide an important food resource that can help bee populations bridge the midsummer gap,” Grab says. Although the nutritional value of hemp pollen relative to other pollens in the bee’s natural habitat is unknown, the variety of bees identified in hemp fields in the Cornell study suggests it’s already making an impact on local bee populations.

During their study, Grab and her colleagues collected a diverse wild and managed bee community from hemp flowers. “The most common species were the European honeybee, Apis mellifera, and the common eastern bumble bee, Bombus impatiens,” she reports. Honeybees comprised 60% of all captured bees, and bumble bees comprised almost 30%. In addition to these two species, they found 14 other species of the family Halictidae, commonly referred to as “sweat bees.” They speculated that the abundance of honeybees likely represented local managed hives. Though a nonnative species, they’re the most important agricultural pollinator in the United States.

“For me, one of the most important findings of our study was that all of the bees that visited hemp are also important pollinators of other crops in the region,” Grab notes. For example, tomatoes bloom at nearly the same time as hemp, and 60% of the pollinators were shared. Hemp plants supported about 20% of pollinators of apples, strawberries, and blueberries. “So by supporting these bee species, hemp may actually promote the pollination of other nearby crops through a process called facilitation,” Grab explains.

Another important finding was that local agricultural landscape and natural habitats influenced bee populations. “We found two factors to be important in explaining variation in the community of bees visiting hemp. First, hemp grown on farms that have a diversity of different crop and noncrop habitats, such as old forests, old fields, and suburban areas had a much greater abundance and diversity of wild pollinators, compared to farms where much of the landscape was devoted only to agriculture,” Grab notes.

Other factors affecting bee visits included plant height and time period. “Tall plants attracted many more bees than did short plants. It may be that tall plants are easier for bees to find, since hemp doesn’t have showy flowers, or this could reflect a preference for fiber varieties that tend to be taller than grain varieties,” Grab says. The number of bees observed during the study also increased throughout the sampling period, which lasted from late July through mid-September. The increasing late-season visits by bees may reflect the scarcity of other pollen and the increasing importance of hemp as a pollen resource when other crops and natural plants have ceased flowering, Grab and her colleagues suggest in their published study.

For Hemp Growers and Hive Owners
Those growing industrial hemp should consider the value of bees to the agricultural community as a whole and modify growing practices accordingly. It’s important to note that only male hemp plants produce pollen, Grab says. Hemp for cannabinoid products is grown in fields with only female plants and won’t support bee populations. Hemp grown for fiber and grain includes male plants and will support bees, she explains. Hemp growers who are aiming for a seed-free flower crop need not worry, as the bees are only collecting pollen. “Bees are not pollinating hemp because they restrict their activity to the male flowers only,” she emphasizes.

Grab notes that hemp provides only pollen, not nectar, so if hemp is the only plant growing across the landscape, bees will do poorly. “For those growing hemp, consider planting other crops that produce lots of nectar, like buckwheat or clover, that can complement the pollen resources that hemp provides bees,” she advises. Hemp growers will also need to consider bees and other beneficial insects when making pest management decisions for their crops as the list of approved pesticides for hemp expands. Avoiding pesticides and weed killers that adversely affect bees is critical.

For hive owners near hemp fields, cannabinoid awareness is necessary. “Hemp pollen has cannabinoids like THC in very low amounts. Beekeepers who place their hives near hemp crops will therefore likely have small amounts of cannabinoids in their hive products,” Grab notes. Knowledge of local and federal regulations around cannabinoids in honey and other hive products is needed, she adds.

But, bees do not have cannabinoid receptors, so they aren’t visiting hemp to get a “buzz,” Grab confirms.

— Jennifer Van Pelt, MA, is a health care researcher and freelance writer located in the Lancaster, Pennsylvania, area.

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