Final report for ONE19-352
Project Information
In fall in temperate climates, beekeepers generally remove stored honey from managed honey bee hives and replace it with artificial feed. This feed, which is often sucrose syrup (SS), high fructose corn syrup (HFCS), or invert syrup (IS), is a much-needed carbohydrate source that will sustain the colony over the winter. In this study we examined the effect of these feeding regimens on colony survival and molecular markers of metabolic health in workers. Full-sized colonies were either allowed to keep their honey (control) or had their honey removed and replaced by one of the three artificial feeds (SS, HFCS, or IS) in fall. Overwintering survival was assessed and overwintered adults and newly emerging, callow worker bees were sampled from surviving colonies in each feeding regimen in March. Overwintering success was significantly higher in colonies that kept their honey and those that were fed IS compared to those that were fed HFCS or SS. We found that the amount of lipid in the fat bodies of overwintered workers correlated with the survival rate of the corresponding feed type. Moreover, vitellogenin and ILP-2 were up-regulated while ILP-1 and JHamt were down-regulated in brain samples of bees that consumed honey or SS relative to those that were fed HFCS or IS. These findings were consistent across overwintered and callow worker samples. In conclusion, bees are more likely to survive the winter and have higher nutritional reserves if they are allowed to keep their honey or are fed invert syrup.
The objective of this study is to compare the effects of various artificial carbohydrate sources compared to a natural honey diet on honey bee health and overwintering survival.
Hypothesis 1: Honey bee colonies fed honey and invert syrup (ProSweet) will have higher overwintering survival than those fed sucrose syrup or high fructose corn syrup (hfcs).
honey = invert syrup > sucrose syrup = hfcs
Hypothesis 2: Gene expression in brain tissue will differ with diet.
For example, Vitellogenin and ILP-2 will be more highly expressed in bees overwintered on honey, while JHamt and ILP-1 will be more highly expressed in bees overwintered on sucrose, invert syrup or hfcs.
Sucrose and high fructose corn syrups (hfcs) have been studied for their effects on honey bees. Research shows that sucrose syrup and high fructose corn syrup are equally accepted by and utilized by honey bees (Severson and Erickson 1984). However, after wintering with the sucrose and hfcs feeds, those with sucrose had higher brood areas in spring (Severson and Erickson 1984), which could lead to larger populations, higher income from pollination contracts, and higher honey production. Lab studies have shown that the lifespan of worker bees is longer when fed exclusively sucrose syrup than when they were fed either honey or hfcs (Barker and Lehner 1978). Studies of the sugar content of royal jelly, the first food of bee larvae and the only food of queen honey bees, showed no impact from various carbohydrate feeds (Sesta et al. 2006). A comparison of sucrose syrup, invert syrup, and starch syrup showed no difference in overwintering mortality in Austria (Brodschneider et al. 2010). In a 2011 SARE-funded project (FS11-252), Barry Harris and David Tarpy studied various winter feeds in North Carolina. In their warm climate, they had excellent survival on all feeds tested, including all of the feeds we plan to use in this study. They also tested the bees for Nosema disease and found no difference between treatments. Most of these studies, however, did not compare the feeds to honey, bees’ natural food, but to each other.
In addition to differences in sugar composition between the feeds there are also other differences. Honey contains pollen, minerals and other ingredients that would be entirely missing from artificial carbohydrate sources. In fact, Mao and colleagues (Mao et al. 2013) determined that there are components of honey that affect the immune system of bees by upregulating detoxification genes. Thus, honey aids in protecting bees because it contains p-coumeric acid, which is missing from other feeds such as sucrose syrup and high fructose corn syrup (Johnson et al. 2012, Mao et al. 2013). This may leave the bees that feed on artificial carbohydrate sources more vulnerable to pesticides and infections. Thus, providing a nutritional diet may be the key to resilience to stress (Doublet et al. 2015, Dolezal and Toth 2018). We are conducting lab assays to look at the effects of diet on gene expression related to nutrition and stress.
The honey bee gut microbiome contains a core set of bacteria, which have been shown to be capable of digesting and metabolizing plant-based carbohydrates (Zheng et al. 2017). This microbiome affects the pH of the gut and impacts bee growth, behavior, hormones and physiology (Zheng et al. 2017). Changes to the core microbiome have been shown to have a negative impact on bees, making them more susceptible to diseases (Hamdi et al. 2011) and impacting expression of vital developmental genes, including vitellogenin (Maes et al. 2016).
The honey bee gut contains microorganisms that aid in digestion (Lee et al. 2015). If the composition of the microbiome is disrupted, it can have a major impact on health. We are interested in understanding whether the type of carbohydrates fed to the bees changes the composition of the microbiome in any way. In addition, gene expression profiles of overwintered adult and newly emerging adult worker bees from the colonies fed various diets will be compared to determine how diet effects core biological processes related to metabolism, immunity, and pesticide resilience.
Cooperators
- - Producer (Researcher)
- (Researcher)
- (Educator and Researcher)
Research
In August 2020, 48 honey bee hives were numbered and randomly assigned to one of four feeding treatments: honey, invert syrup (prosweet), high fructose corn syrup, or sucrose syrup (2:1). Honey supers were removed, extracted and replaced to give the bees room to store the feed. Feed was added, up to 5 gallons per hive. Each hive was fitted with an automated scale (broodminder.com), which automatically records hive weight each hour.
In March 2021, colony survival was assessed and select surviving colonies from each treatment were sampled. Adult worker bees which had overwintered were collected from the cluster and callow bees were collected at the time of emergence and placed on dry ice prior to storage at -80oC. We partially dissected these bees, separating the head, thorax and abdomen and placed in an eppendorf tube with 200 ul RNAlater-ICE and stored at -20oC for 48h before being stored at -80oC. Total RNA was extracted from brain tissue samples and sequenced. The resulting data were run through a transcriptome analysis to investigate differences in gene expression between bees fed different diets.
By spring of 2021, of the 48 colonies, 25 colonies were living: 4 that were fed high fructose corn syrup, 5 that were fed sucrose syrup, 7 that were fed invert syrup and 8 that were allowed to overwinter on naturally-collected honey. In previous studies, Brodschneider et al (2010) saw no difference in overwintering success between colonies fed sucrose syrup, invert syrup, or starch syrup and Harris and Tarpy (FS11-252) had excellent wintering survival using various non-honey feeds. However, they did not compare these types of feed to honey, as we did in this study. We found that sucrose and high fructose corn syrup had equally poor survival while invert syrup and honey had equally good survival. These differences are statistically significant (X2 test, p=0.0031).
The bees in our study consumed, on average, different amounts of food over the course of the winter. By spring of 2021, surviving colonies that were fed high fructose corn syrup had consumed, on average, 42 lb of food, those that were fed sucrose syrup had consumed 33 lb of food, those that were fed invert syrup had consumed 41 lb of food and those that were allowed to overwinter on naturally-collected honey consumed only 19 lb of food. Thus, bees fed artificial diets consumed more food than those consuming natural honey. However, the cost of artificial feed is far lower than the value of honey, so it is still economical to extract and sell honey and to feed bees other sources of carbohydrates if profit is a motive.
Mao and colleagues (Mao et al. 2013) determined that there are components of honey that affect the immune system of bees by upregulating detoxification genes. Thus, honey aids in protecting bees because it contains p-coumeric acid, which is missing from other feeds such as sucrose syrup and high fructose corn syrup (Johnson et al. 2012, Mao et al. 2013). This may leave the bees that feed on artificial carbohydrate sources more vulnerable to pesticides and infections. We conducted a lab assay to look at the effects of diet on gene expression related to nutrition and stress in bees that are overwintered on different types of food. We have found that, compared to bees fed honey, vitellogenin and ILP-2 were down regulated in bees from colonies that were fed invert syrup and high fructose corn syrup. In contrast, these were up regulated in bees from colonies that were fed sucrose syrup. Interestingly, JHamt and ILP-1 had the opposite results, being up regulated in colonies fed invert syrup and high fructose corn syrup, but down regulated in bees fed sucrose syrup. Also of interest is that these results were the same for bees that overwintered on these types of food (adults) and those that developed in the very early spring being fed by these adults (callows), but with no direct contact with the food.
Overwintering survival differed based on the feed that was provided the previous fall. The chance of survival was almost double in colonies that were allowed to keep their naturally-collected honey and those that were fed invert syrup (prosweet) over others that were fed high fructose corn syrup or sucrose syrup. Thus, for improving survival, beekeepers may choose to rely on honey and invert syrup rather than HFCS or sucrose.
Gene expression is different in bees fed different diets. Gene expression profiles for candidate genes were almost identical for invert syrup and high fructose corn syrup fed bees while sucrose group was more similar to honey despite a small, significant difference in expression levels in all tested genes. We found that the amount of lipid in the fat bodies of overwintered workers correlated with the survival rate of the corresponding feed type. Moreover, vitellogenin and ILP-2 were up-regulated while ILP-1 and JHamt were down-regulated in brain samples of bees that consumed honey or SS relative to those that were fed HFCS or IS. These findings were consistent across overwintered and callow worker samples and consistent with the higher nutritional reserves seen in physiologically younger individuals.
Education & Outreach Activities and Participation Summary
Participation Summary:
January 2022. Underwood RM, Döke MA, Ortiz-Alvarado Y, Koru BY, Giray T. You are what you eat: Effect of fall feeding regimen on the overwintering success and gene expression profiles of honey bees. North American Bee Research Conference, virtual.
February 2022. Dr. Robert Currie discussed the results of this study with Calgary Beekeepers, Alberta, Canada.
March 2022. Does Fall Feed type impact overwintering success & health of honey bees? summarized for PA's Apiary Advisory Board
September 2022. Does Fall Feed type impact overwintering success & health of honey bees? Northern Virginia Bee Association, virtual.
The abstract from this presentation was published with the conference proceedings in Bee Culture magazine (https://www.beeculture.com/abrc-proceedings/).
The scientific journal article will be submitted to the Journal of Insect Physiology in January 2023.
Learning Outcomes
Some farmers who attended the presentations changed their feeding based on this work.
Project Outcomes
nothing yet to report
This project has moved along very slowly. Mainly the added laboratory studies, which are a crucial new avenue of research, are very time consuming. Here, we report the results of brain tissues studies. However, we have samples and plans to also analyze other parts of the body. In addition, an entire project is being build upon the microbiome of the gut of the collected bees. These studies will be conducted in 2023 and beyond without further funding.
It is clear from our results that further studies of the impacts of fall feeding on bees are necessary. Some beekeepers feed other things, such as fondant, during the winter, so this should be added to analyses in the future.
I do feel that we answered the question we set out to answer with this project. We are beginning to understand the impacts of beekeeping practices for overwintering honey bee colonies. As we investigate each piece of the puzzle, we move toward better success for beekeepers. I will continue to speak and write about the results we found so more beekeepers can learn and think about how they are feeding their bees.