The macronutrient regulation of adult worker honeybees

World agriculture relies on insects to pollinate flowering crops, especially soft fruit, vegetable, and nut crops, that are increasingly forming the basis of most human diets. As our diet shifts from grains and cereals to including more vegetables and fruits, the demand for these services continues to grow in step with the world's population. In fact, human consumption of fruits, nuts and vegetables that require pollination has increased as much as 300% in the past 50 years. In addition, other crops that improve seed set when pollinated such as oilseed rape are important for food but are also potential biofuels. Pollinators, and their well-being, are important to our future health and survival.

Domesticated bees are the most important pollinators used in world agriculture. Commercial honeybee keepers maintain thousands of colonies, transporting them to orchards or other agricultural field settings to perform pollination services. Commercial beekeepers often struggle to find enough pollen to feed their colonies, especially at times of year when natural forage is scarce. Insufficient nutrition is one of the main factors for the poor health in honeybee colonies that are beset by pathogens and parasites, as well as exposed to a diversity of agricultural pesticides. In the past 20 years, beekeepers have started to rely on feeding colonies with commercial pollen substitutes but these substitutes are not scientifically formulated and do not have all of the essential nutrients bees need.

Our recent BBSRC-funded research investigated the adult worker honeybee's nutritional needs. We found that adult worker bees self-select proportions of protein and carbohydrate and that their demands for protein and carbohydrate change as a function of their caste. In addition, foods high in protein or essential amino acids reduce survival. We also found that the proportion of essential amino acids in diet affected the regulation of protein intake. Our recent work indicates that diets too high in fat shorten adult worker bee lifespan, and that the proportions of essential fatty acids in food affect learning performance and glandular development in adult worker honeybees.

Here, we propose to extend our research on bee nutrition to identify how bees regulate their protein, fat, and sterols. Our experiments will also examine how sources of proteins, fats, and sterols can be combined to produce mixtures that meet the honeybee's needs for essential nutrients. We will start by testing the digestibility of several potential protein sources and their effect on the intake of food in adult worker bees. Extending our previous research, we will test how the proportion of essential amino acids in dietary protein affects the total amount of protein bees consume. Fat is an important nutrient for bees, and makes up nearly 30% of the dry weight of royal jelly (i.e. glandular secretions fed to larvae and the queen) but is only found at between 5-7% of the dry weight of pollen. In our proposed experiments, we will identify the relative ratio of protein to fat needed by adult worker bees in the presence and absence of brood. Bees also need a dietary source of phytosterols that are found in pollen. We will also perform experiments that test how much of these sterols adult worker bees need to rear brood successfully. Our experiments will lead to a final test of a combination of protein, fat, carbohydrate, and sterols in whole colonies compared to the performance of bees fed with natural pollen. With this information, we will be able to provide advice to beekeepers on the materials and their combinations that can be used to formulate substitutes for pollen when pollen is unavailable.

Pollination provided by domesticated honeybees is critical in agricultural systems where flowering plants are obligated to outcross (e.g. apples). Providing sufficient pollen forage for bees is a challenge in landscapes under heavy agricultural cultivation. Beekeepers face many difficulties such as disease, parasites, and pesticides that are exacerbated by poor nutrition. In response, beekeepers often feed colonies with substitutes for pollen that are indigestible or do not provide all of the essential nutrients bees need. Here, we propose to extend our work on bee nutrition to advise beekeepers about ways they can supplement bee diets when pollen is scarce. Our proposal has three main aims: (1) to identify how bees digest and regulate their intake of protein relative to other nutrients; (2) to identify the optimal amount of essential fats and sterols bees need in diet; and (3) test a predicted 'optimal' mixture of macronutrients on entire colonies. We will start out by testing the digestibility of potential protein sources. Using the Geometric Framework for nutrition, we will measure how the proportions of essential amino acids in food affect the regulation of protein intake. We will also identify the optimal protein-to-fat ratio for honeybees. These experiments will include manipulations of the relative proportions of the total amount of the two essential fatty acids (linoleic and a-linolenic acid) in diet that we know are important for bee development and performance. Critically, we will identify the amount of 24-methylene cholesterol (an essential sterol) needed by adult worker honeybees with and without brood. Finally, we will test our predicted optimal combination of these materials in whole colonies against the performance of colonies fed with natural, honeybee collected pollen. This information will enable beekeepers to feed bees with the best substrates and their correct proportions in the absence of pollen and hence will impact world agriculture.

World agriculture relies on pollinators for the production of soft fruits, nuts, seeds, and vegetables. In large scale agriculture such as almond orchards in California, pollination services are primarily accomplished by honeybee colonies that are transported to orchards and fields by the millions during flowering. Commercial beekeepers are paid for each colony they bring to a field site. Prior to flowering, these colonies may not have access to much pollen, which means it is difficult to build up the colony's size and strengthen health. To overcome pollen dearth, beekeepers in the past 30 years have started to use bee feeds made from grains like soya beans: products that are inexpensive and easy to obtain. The base products are purchased from beekeeping suppliers, mixed with sugar solutions (e.g. high fructose corn syrup) in the field, and then provided to the bees as a patty or a liquid food within the colony. Beekeepers sometimes make and mix their own formulations. A major problem with these feeds is the fact that they do not provide essential nutrients (e.g. correct fatty acids and sterols). These base materials (e.g. soy) are also difficult for bees to digest and have been reported to cause dysentery. They are also not formulated in a way that optimizes combinations of macronutrients for honeybees. In fact, to make these substances palatable to bees, beekeepers add ~5-20% honeybee collected pollen to the mix, but this is very expensive and has the potential to spread disease and expose bees to pesticides.

Our proposed research will have a large impact on the beekeeping industry and agriculture. At present, there is a pressing need in the commercial beekeeping industry for bee foods that are substitutes for pollen. To obtain natural forage for their bees, beekeepers also transport their colonies to places where forage is available. This is expensive and stressful for bees. Having a substitute for pollen that did not require the addition of bee collected pollen would reduce the need to transport bees to forage and reduce risk associated with exposure to pathogens from bee collected pollen. Native bees compete with honeybees for access to natural pollen and nectar; a pollen substitute for honeybees would also reduce competition for floral resources in natural habitats and improve wild bee populations.

Presenting our research at international beekeeping conferences and local meetings, we have realized that beekeepers worldwide are very keen to find a way to improve the nutrition of their colonies. This need motivated us to focus our nutrition work towards the goal of producing food that could be used when pollen was unavailable. The research described in our proposal will provide the following: 1) specific information about the nutritional needs of honeybees; 2) information about raw materials that can be used as food in bee colonies; 3) insight into nutrient balancing by social insects, especially for proteins, fats, and sterols. As part of our impact plan, we will begin the process of commercialization of the information we obtain here by applying for BBSRC Follow on Funding and starting a spin-out company that will develop and orchestrate the production of bee feeds. The research described in this proposal will guide our potential future commercialization of this information. The data we produce from this work will also be published in scientific journals and interpreted and made available to beekeepers via a website managed in association with the British Beekeeping Association. This information will permit beekeepers to improve upon their methods of feeding and will improve pollination services for agricultural crops worldwide.