Progress report for ONE19-352
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. Honey bee worker digestive health and pesticide resilience will also be determined.
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.
honey = prosweet > sucrose = hfcs
Hypothesis 2: Consumption rate of the four winter foods will be equal.
honey = prosweet = sucrose = hfcs
Hypothesis 3: The honey bee gut microbiome will be changed by all three artificial feeds as compared to honey.
honey ≠ sucrose or hfcs or prosweet
Hypothesis 4: Gene expression will differ with diet across multiple tissues.
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, prosweet 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 (Table 1) 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 realted to metabolism, immunity, and pesticide resilience.
- - Producer (Researcher)
In August 2020, 48 honey bee hives were fitted with broodminder scales and temperature monitoring devices. These allow for continuous monitoring of ambient and in-hive temperature and overall hive weight. Data is being collected to determine the rate of colony weight loss over the winter.
The hives were numbered and randomly assigned to one of four feeding treatments: honey, prosweet (invert syrup), 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.
In March 2021, select 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 paritally dissected these bees, separating the head, thorax and abdomen and placed in an eppendorf tube with 200 ul RNAlater-ICE ad stored at -20oC for 48h before being stored at -80oC. Total RNA was extracted from these samples and will be sequenced. The resulting data will be 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 fructore 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 surivial 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 fructore 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 sonsumed 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 are actively conducting lab assays 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.
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). We are actively conducting lab assays to look at the effects of diet on the gut microbiome of bees that overwintered eating the various types of food and of bees raised by those bees that had fed on that 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. How these changes will impact the individual bees or the colony are a subject for future study.
Full transcriptome work from brain, flight muscle, and fat body samples is currently underway. In addition, the impacts of these feeds on the honey beeworker bee gut microbiome have yet to be determined.
Education & Outreach Activities and Participation Summary
A talk was given at the North American Bee Research Conference, which was held virtually. Here is the citation.
Jan. 12, 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.
The abstract from this presentation will be published with the conference proceedings in Bee Culture magazine.
Further activities will occur at the end of the project, when we have further results.
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