Researchers improve honeybee health by modifying yeast to produce the substances in pollen.
Introduction
Good nutrition is as important for honeybees as it is for humans. Where do honeybees get their nutrition? Honeybees eat nectar and pollen from flowers. Pollen provides honeybees with nutrients including proteins, fats, and micronutrients. If honeybees cannot find enough food, they may become sick. Worker bees may stop taking care of larvae and pupae. They may even abandon the hive, leaving the queen and babies behind. When this occurs, the colony collapses.
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When bees transition from a larva to an adult, they pass through a stage called pupation. In this stage, the bee larva stops eating, spins a cocoon, and the worker bees create a wax cover for the cell called a cap. One sign of a colony’s health is the number of capped pupal cells. These caps indicate that the larval bees received enough food from the workers and will become adult bees, too.
Without healthy honeybee colonies, it is difficult to grow many crops that are important parts of human diet. That’s because honeybees are pollinators. When they gather food from flowers, honeybees transfer pollen from one part of the plant to another. This causes the flowers to produce seeds and fruit that we harvest. Without honeybees, orchards and fields would produce less food, and food prices would increase.
To maintain honeybee populations, beekeepers started feeding human-made pollen substitutes to their honeybees. But the food they use does not meet the nutritional needs of the honeybees. These substitutes do not include all the sterols found in flower pollen. Sterols are a group of chemicals used to build cell membranes and make hormones. Honeybees cannot make sterols on their own. They must get them from their diet. That is why we wanted to develop a new food additive for honeybees. We wanted to put this additive in the human-made food for honeybees so they can have the sterols they need to be healthy.
Methods
We analyzed honeybee tissue to determine the type and amount of sterols honeybees use. We measured the sterols in queen, worker, and male pupal tissue. Then we genetically engineered a type of yeast called Yarrowia lipolytica so that it would produce a mixture of these sterols. We grew the yeast to make enough to feed the honeybees. Then we dried and ground it into a powder to make it easy to add to honeybee food.
We fed small colonies of honeybees one of three diets for three months. All three diets included human-made honeybee food with important nutrients like protein. The test diet contained our modified yeast. The other two were our control groups: one diet contained unmodified yeast (without added sterols), and the other did not contain any yeast.
During the feeding period, we counted the number of eggs, larvae, and capped pupal cells every 15 days (Fig. 1). Then we compared the number of eggs, larvae, and pupae for the three diets from Day 45 to Day 91. We also compared the results to data from colonies fed with natural pollen and colonies starved of pollen.
Results
We learned that honeybees require six sterols from pollen. All honeybees used the same sterols, but the amounts of each differed in worker, queen, and male pupae.
We discovered that there was no relationship between the number of eggs and diet. However, by Day 75, the colonies fed the mixed-sterol diet had produced more larvae. We found that the mixed-sterol colonies had a greater number of pupae as well (Fig. 2). At the end of the experiment, the mixed-sterol colonies had between 10 and 40 capped pupal cells. There were no capped cells in the colonies that received an unmodified yeast diet. There were between one and three capped cells in colonies that received no yeast.
Discussion
Our mixed-sterol yeast provided essential nutrients to honeybees. Without the added sterols, the number of honeybees reaching the pupal stage was much lower. The numbers of pupae in the control groups at the end of our experiment matched the numbers in colonies starved of pollen. Adding a mixed-sterol yeast caused more honeybees to reach the pupal stage and survive into adulthood. This is comparable to colonies in similar conditions but who also had access to pollen.
Our honeybee food additive will be important for beekeepers to maintain their hives. It will help beekeepers provide food that promotes population growth during dearth periods. These are times when there are few to no blooming flowers. Dearth periods occur when it is too hot or too cold for plants to bloom. They also occur when there is a drought. While these periods occur naturally, climate change increases their frequency. Land use changes can also decrease the amount of pollen available. For example, transforming natural areas into cities or farms. Using mixed-sterol yeast will provide the honeybees with the food they need. This will help against the decline of honeybee populations.
Conclusion
You can support honeybee populations in your own community. The next time you plant flowers, select bee-friendly plants. These plants will be pollen- and nectar-rich. And many will be native to your area. If you are not sure which plants are the best for your yard, garden, or window boxes, ask at a local garden store. They will help you pick the best plants. You can also keep honeybees healthy by protecting their habitat. Support organizations and government programs that protect open spaces. By making sure that there are plenty of bee-friendly flowers in your community, you can help keep local honeybees healthy.
