The influence of diet on the honeybee lipidome

Domesticated honeybees are arguably the most important pollinators in the world. Millions of commercially-managed honeybee colonies pollinate vegetables, soft fruit, nuts and oilseed crops every year, ensuring human food security. Honeybees also make important economic contributions to human welfare through honey, wax, and other products such as royal jelly. In the past 15-20 years, intensive management of honeybee colonies has made them more vulnerable to the global spread of pathogens and parasites. In some settings, bees are exposed to a staggering array of agricultural chemicals including pesticides, fungicides and herbicides. Changes to landscape management have reduced the diversity and abundance of flowering plants throughout the world, with concomitant effects on the food available for bees. To overcome these shortages, beekeepers now routinely feed artificial pollen substitutes with unbalanced nutrition that makes bees susceptible to diseases like dysentery. All of these factors are leading to severe colony losses each year in areas where bees are intensively managed.

Nutrition plays a critical role in animal health and welfare. The main source of nutrition of honeybees is floral pollen and nectar. Nectar provides carbohydrates whereas pollen provides protein, fat, and micronutrients. Many studies of bee nutrition have focused on the importance of protein, but few have examined the role of fat. Lipids are important components of cell membranes but are also used as signalling molecules and for energy storage. Animals can synthesize lipids de novo from carbohydrates, but some lipids must be acquired from diet. These lipids include essential fatty acids such as the polyunsaturated fatty acids linoleic and alpha-linolenic acid. Insects, unlike mammals, also require a dietary source of sterols. An important discovery from our team identified that the essential fatty acids found in pollen directly impact the nutrition and behaviour of adult worker honeybees. Bees with the incorrect amount of alpha-linolenic acid (so called 'omega-3') exhibit poor learning abilities. Such diet-induced changes to behaviour could have a serious impact on a bee colony, because foraging bees must learn floral traits to acquire pollen and nectar.

The research proposed here is poised to make important discoveries regarding the role of lipids in a honeybee colony. We plan to investigate how natural lipids in the pollen and bee bread consumed by nursing-age worker honeybees are taken up and converted into glandular secretions (e.g. royal jelly) fed to larvae. We will quantify how these lipids are distributed within the tissues of adult and larval bees. Using advanced methods developed in our laboratories and state-of-the-art methods for lipidomic analysis, we will map the transformation of dietary fatty acids and sterols into fat compounds found in bee guts, brains, reproductive organs, fat bodies, and brood food glands. Our research will also identify how fats in diet influence the quality of food given to larvae, and whether diet-induced alterations to fat in larval food affect development. Our ultimate goal will be to test how dietary fats influence the longevity of foragers and whole colony performance in a field setting. With these data, we will advise the beekeeping industry of best practice for the use of fats in substitutes for pollen. Using these data, land managers can also choose plants that provide the correct fatty acid and sterols in pollen for flower strip planting in agroecosystems. For these reasons, our research will lead to the improvement of welfare of domesticated bees. It has the potential to make a significant contribution to the enhancement of global food security through its impact on pollination services.

Lipids are the substrates of membranes, precursors for hormones, and the means for energy storage in animals. Dietary lipids, such as the polyunsaturated fatty acids linoleic and alpha-linolenic acid, alter the composition of lipid species in an animal's tissues with impacts on animal health, longevity, and fecundity. The impact of dietary lipids on the corporeal lipidome could be greater in insects than mammals, because they cannot synthesize polyunsaturated fatty acids (FAs) or sterols. It is currently unclear how diet modifies an organism's entire lipidome. Honeybees acquire protein, lipids, and micronutrients from floral pollen, but their requirements for dietary fat are poorly characterized. We will test how FAs and sterols in diet affect the entire lipidome of every caste and life history stage in a honeybee colony. We will employ state-of-the art lipidomics to study how specific lipids are incorporated into tissues such as the brain, fat body, and gut. By rearing adult workers in the lab on chemically defined foods previously designed by our team, we will test how FAs affect the regulation of dietary protein, fat, and carbohydrate. Through prior BBSRC funding, we have developed specialized methods for studying whole colony nutrition by feeding small colonies in an enclosed setting with no access to external pollen and nectar. Using this approach, we will also study how the FA composition of food eaten by adult workers affects lipids in the glandular secretions fed to the developing larval workers, queens, and drones. In the field, we will measure how dietary FAs affect the performance of whole colonies with a focus on the foraging worker bee. These data will provide the foundation for studies of the role of fats in bee health and will provide valuable insight towards the importance of dietary fats in the honeybee life cycle, information critical to improving bee welfare.

World agriculture relies on pollinators for food security. In many modern agricultural settings where fruits, vegetables, and nuts are cultivated, pollination is accomplished by honeybee colonies. Plant diversity is usually low in agricultural settings, making it difficult for pollinators to acquire the nutrition they need. Beekeepers now routinely supply honeybee colonies with food to augment the lack of pollen in the landscape. They can purchase food substitutes for pollen, but these substitutes lack essential nutrients. None have been formulated in a way that optimizes combinations of macro- and micronutrients for honeybees. In some cases, they are also made with cheap materials that can cause dysentery.

Unlike other domesticated animals, the nutrition of honeybees has lagged behind. Using information from our basic research on nutrition funded by the BBSRC, we predicted which combination of nutrients would optimize bee performance. These ideas were patented in 2015. By testing many potential substrates, we have created a pollen substitute for honeybee colonies that enhances brood and honey production and reduces Nosema (a gut parasite) load compared to leading commercially-available products. These endeavours, supported by a BBSRC responsive mode grant, an Enterprise fellowship, Follow on Funding, led to the formation of a university spin-out company with the ultimate aim of making foods that improve nutrition for domesticated bees worldwide.

The basic research proposed here will identify the distribution of fats in bee bodies and how fatty acids and sterols in diet influence bee longevity and development. Based on our research, we know that fats are a critical ingredient in any supplementary food that replaces pollen. These experiments will permit us to test many sources of fatty acids that could be added to supplemental foods. An exciting facet of our research will also identify how diet influences the honeybee's glandular secretions (e.g. royal jelly) to affect larval development. The insight gained from these experiments could lead to future innovations in foods designed to optimize queen and drone performance. Our data will also reveal which fatty acid sources and sterols will optimize whole colony performance. In addition, these data could be generalized to identify which plant species' pollen is best for honeybees. This information could be used to inform land managers of which plants are best to cultivate in field margins to improve pollinator welfare in agricultural landscapes.

The data we produce from this work will be protected by intellectual property agreements at our respective universities. We will publish our results in scientific journals and translate our findings for beekeepers through articles in beekeeping magazines, talks at beekeeping conferences, and through our own websites. We expect that the data from our proposal will permit beekeepers to improve upon their methods of feeding and will have a significant, positive impact on pollination services for agricultural crops worldwide.