by Sally Colby
Honeybee health is important to growers who rely on bees for pollination. Dr. Ramesh Sagili, associate professor of apiculture, Oregon State University, believes one of the biggest issues in maintaining healthy bees is nutrition.
Sagili said poor nutrition can be the result of monocropping that leads to lack of forage and loss of habitat. Suboptimal nutritional supplements contribute to poor nutrition as well as pesticide exposure, environmental stressors and physiological stress resulting from transportation.
Nutrition plays a role in colony decline, which is attributed to multiple factors including the Varroa mite, an ectoparasite that feeds on the abdominal fat and blood of the bee. Varroa mites also transmit several viruses that affect bees. Pathogens such as viruses, bacteria and fungi also affect bees. “The European honeybee is not native to North America,” said Sagili. “They were introduced 400 years ago so we also have some issues with genetic diversity.”
Honeybee nutrition is directly impacted by what bees eat, so good nutrition is the first line of defense against many bee problems. Numerous studies have documented that optimal nutrition boosts bees’ immune systems and helps produce detoxifying enzymes that assist bees in ridding some of the toxins entering their systems.
“Compared to other insects, especially solitary insects, honeybees have more complex nutritional needs,” said Sagili, adding that colony nutrition, adult nutrition and larval nutrition are critical. “Larval needs are very different from bees that are being fed aggressively by nurse bees. Adults are feeding on nectar or honey collected from plant resources, and pollen is their protein source.”
Colony level nutrition is influenced by the number of bees in a colony, available resources and the caste system within the hive. In addition, bees perform different tasks that require varying levels of nutrition. For example, a forager may not need much protein as a nurse bee.
Like the plants they feed on, bees require both macro- and micronutrients. Sagili said there’s a lot of knowledge about macronutrients, which are categorized as carbohydrates such as the nectar and honey collected and used for daily energy needs. There’s also information about proteins such as pollen – bees’ only protein source. “All pollen is not equal,” said Sagili. “The range of protein in most pollens is 10% to 40%. Pollens are also a source of lipids (fats), as well as minerals and vitamins.”
There isn’t as much knowledge about critical micronutrients such as vitamins, minerals and lipids. Lipids include fats, phospholipids, sterols and waxes. “Honeybees have been studied for more than 200 years in the modern world but we still have a huge gap in knowledge regarding micronutrients,” said Sagili. “That makes managing micronutrients more difficult.”
In insects, sterols are components of cell membranes and precursors of molting hormones. All insects get sterols from their diet. Molting hormones are passed to larvae by the bee after foraging. “Bees feed on pollen from plant resources,” he said. “Bees feed larvae, and that’s how the larvae get sterols. Beekeepers also give protein supplements at a certain point of the year when there is a pollen dearth. There is no sterol in artificial diets, so bees can’t feed sterols to larvae. The larvae may desiccate and will not molt – no sterol, no molting hormones.” Sagili added that while nutritional supplements for bees are better than nothing, they lack micronutrients.
Sagili said most bee nutrition work was conducted in the 1980s and ‘90s, but more recent research over the past five years has targeted nutrition. Current research is focused on evaluating dietary sterol requirements of honeybees and examining sterol composition of forages available to bees with the goal of determining a balanced diet.
Nutritional challenges facing honeybee colonies during crop pollination include insufficient pollen, lack of pollen diversity and poor pollen quality. Sagili reviewed a recent study in which pollen traps were used to determine how much pollen bees were collecting. Researchers found various levels of pollen for various crops, noted in grams per colony per week: Cherries, 533; almonds, 303; blueberries, 81; hybrid carrots, 14.
Providing supplemental forage improves bee health and crop yield, so the effort is a win-win for beekeepers and growers. Sagili said it’s often difficult to persuade farmers to invest in efforts to provide supplemental nutrition because many are already paying for pollination services. “On top of that, to plant something for bees is a lot of work and expense,” he said. “But it’s worth it because optimal nutrition means there is adequate pollen in the hive, which will stimulate the queen to lay eggs and produce larvae. A greater number of larvae means they’re releasing a lot of pheromones.”
Pheromones are used by larvae to communicate to adult bees. Adults perceive the pheromones and determine whether there are 1,000 larvae one day and 2,000 larvae the next, and that’s how bees receive cues to start foraging for resources (pollen and nectar). More larvae means more foraging trips and more pollen. “When you’re stimulating them with the pheromone from the larvae,” said Sagili, “there are more bees on the flowers of the crop and that will increase yield because of increased pollination.” Sagili noted that the queen will stop laying eggs when there is no pollen coming in, which eventually impacts pollination.
Promotion of habitat improvement for bees in both rural and urban areas is helping to preserve bee health. Limitations growers face in establishing supplemental forage include land availability, irrigation that influences bloom time, weed management and matching bloom with bees’ needs. Bees remain in the crop for pollination for about a month during bloom, and after that there’s no value from that crop to them.
Despite the benefits of habitat, there are concerns regarding potential decrease in target crop pollination. If a grower is paying for a certain number of hives but has planted supplemental forage, will it distract the bees from the target crop and reduce pollination?
Plant lists indicating favorable species for bees help growers decide what to plant for pollinators, but the information is not based on empirical research. Current plant lists are based on plants’ attractiveness to bees – where are bees seen? What Sagili wants is a database that indicates not only attractiveness but also pollen nutritional composition to allow growers to select species for pollinator plantings based on comprehensive information. To that end, Sagili is developing a pollen nutrition composition database. “We need to know the nutritional composition too,” he said. “Attractiveness is not enough.”
Bee friendly certification programs benefit growers as well as consumers who are interested in bee health. The “Bee Better Certified” program through Xerces Society requires a minimum of 5% of land dedicated to bee habitat, establishing suitable nesting sites (undisturbed growth, plants with pithy stems) and protecting bees from pesticides through management strategies such as monitoring, non-chemical practices and limiting or eliminating high-risk pesticides. Bee Friendly Farming® encourages establishing pollinator food resources, providing nesting habitat and incorporating IPM.
NRCS compiled a list of pollinator-friendly plants with information about pollinator value, plant characteristics, bloom time and habitat available at nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/nypmctn11164.pdf.