To save honey bees we need to design them new hives

Published: September 9, 2019 1.22pm BST Updated: September 12, 2019 10.20am BST

Author

• Derek Mitchell PhD Candidate in Mechanical Engineering, University of Leeds

Disclosure statement

Derek Mitchell is affiliated with Institute of Thermofluids, School of Mechanical Engineering, University of Leeds

 

Honey bees are under extreme pressure. Beekeepers in the US have been losing and then replacing an average of 40% of their honey bee colonies every year since 2010, a rate that is probably unsustainable and would be unacceptable in other kinds of husbandry. The biggest contributor to this decline is viruses spread by a parasite, Varroa Destructor. But this isn’t a natural situation. The parasite is spread by beekeeping practices, including keeping the bees in conditions that are very different from their natural abode of tree hollows.

A few years ago, I demonstrated that the heat losses in man-made honey bee hives are many times greater than those in natural nests. Now, using engineering techniques more commonly found probing industrial problems, I’ve shown that the current design of man-made hives also creates lower humidity levels that favour the Varroa parasite.

Natural nests inside tree cavities create high humidity levels in which honey bees thrive and which prevent Varroa from breeding. So if we can redesign beekeeper hives to recreate these conditions, we could help stop the parasite and give honey bees a chance to recover.

The life of the honey bee colony is intimately entwined with its home. We can see this from the sophisticated way honey bees choose nests of the correct sizes and properties, and how hard they work to modify them. In fact, the nest can be seen as part of the honey bee itself, a concept that in biology is known as an “extended phenotype”, which refers to all the ways a creature’s genes affect the world.

 

Perhaps the most common example of an extended phenotype is that of the beaver, which shapes its environment by controlling the flow of water with dams. Nests enable honey bees to similarly adjust their environment by controlling the flow of two fluids – air and water vapour – plus something that acts like a fluid – heat.

The honey bees select a tree hollow with an entrance at the bottom that makes rising hot air inside the nest less likely to escape. They then modify it by applying an antibacterial vapour-retarding sealant of tree resin over the inside walls and any small holes or cracks. This further prevents any warm air leaks and helps maintain the right level of water vapour. Inside the nest, the bees build a honeycomb containing thousands of cells, each of which provides an insulated microclimate for growing larvae (baby bees) or making honey.

Unnatural designs

Despite the importance of nests to honey bees, the hives we build them bear little resemblance and have few of the properties of the natural tree nests European honey bees evolved with. In the 21st century, we’re still using hives designed in the 1930s and 1940s, based on ideas from the 1850s. Natural nests were only scientifically surveyed as recently as 1974 and research into their physical properties only began in 2012.

Man-made hives are squat and squarish (for example 45cm high), constructed from thin wood (under 2cm thick) with large entrances (around 60cm²) and often large openings of wire mesh underneath. They were designed to be cheap and for beekeepers to easily access the bees and remove the honey. In contrast, European honey bees evolved with natural tree nests that are on average tall (around 150cm), narrow (20cm) with thick walls (15cm) and small entrances (7cm²).

 

Man-made hives versus natural nests. Derek Mitchell

In order to assess how well man-made hives recreate the conditions of natural nests, I needed to measure the flow of fluids (air, water vapour and heat) around them. To do that, I turned to an aspect of physical science and engineering called thermofluids, the study of liquids, gases and solids of combustion, and changes of state, mass and energy movement.

In the honey bee nest, this means the “combustion” of sugars in honey and nectar, the evaporation and condensation of water, and air flow through the nest. It also includes everything being transported by the honey bees through the entrance or leaking through the walls.

The various barriers that honey bee nests create can be used as convenient boundaries in mathematical models of the energy needed and humidity produced inside the nest. My new study combines these models with data from experimental research on the thermal properties of honey bee nests and hives and behavioural studies on how honey bees ventilate their nest.

This enabled me to compare the average humidity in man-made hives and tree nests with that needed by honey bees and their parasites. I found that most man-made hives have seven times higher heat loss and eight times bigger entrance size than tree nests. This creates the lower humidity levels that favour the parasite.

My research shows the role of the honey bee nest is clearly far more sophisticated than just simple shelter. Simple changes to hive design in order to lower heat loss and increase humidity, for example using smaller entrances and thicker walls, could reduce the stress on the honey bee colonies caused by Varroa Destructor. We already know that simply building hives from polystyrene instead of wood can significantly increase the survival rate and honey yield of the bees. More research into the thermofluidic complexity of nests would allow us to design the optimal hives that balance the needs of honey bees with their human keepers.

This article has been amended to make clear that the average 40% of US honey bee colonies lost each year are replaced.

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Honey bees vote to decide on nest sites – why we should listen

Published: July 1, 2024 1.12pm BST

Author

• Derek MitchellResearcher in Mechanical Engineering, University of Leeds

Disclosure statement

Derek Mitchell does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

 

When people think of honey bees, they often think of classic wooden hives, in which beekeepers are having to breed more and more bees just to keep managed populations stable. These man-made boxes, designed to facilitate pollination and honey production in an era before animal welfare was considered, are the hives in which scientists study honey bees.

However, these boxes have little in common with the wild nests that featured in honey bee evolution. Are we are missing something from the evolution of wild bees that might help managed bees today?

Honey bees, originally a tropical insect, colonised cold climates 600,000 years ago by evolving complex behaviour patterns for finding and selecting nest cavities in trees.

Swarming honey bees send out scouts to find suitable nests, measure them for fitness against a list of criteria such as height off the ground, volume, entrance size, and entrance location. They communicate this information to the rest of the scouts. Then the scouts engage in a voting system to select the best one and move the entire swarm sometimes over a kilometre to the new nest.

 

 

This tells us that these nests were not that common, even 600,000 years ago. However, the survival advantages warrant investing enormous amounts of energy in finding them.

Disease, predators, parasites and climate change are threatening the future of managed honey bees, pollinators of our food crops. Yet research into these pressures and honey bee behaviour rarely takes account of the nest preferences of honey bees shaped by evolution.

For example an international survey of honey bee losses conducted by the Federation of Irish Beekeepers has only three yes/no questions about hives and bee research has no methods or standards on how to evaluate the quality of hives, in contrast to the elaborate measures taken by the bees themselves.

Have we, by putting honey bees into boxes for our own convenience, prevented bees coping with these pressures? Do the bees’ elaborate nest-choosing suggest strategies to help protect them?

One way to answer these questions would be to quantify the physical properties of man made research hives, in relation to the preferences of the honey bees and the context they evolved in. This would mean we could give a hive a scientifically based score relevant to the long term survival of honey bees. It would also form a basis for researching whether human built hives are helping or hindering the honey bees.

 

Do we make hives that are best for bees or ones that make life easier for humans. kosolovskyy/Shutterstock

My research  used the science methods more commonly used for aerodynamics and building simulations (computational fluid dynamics or CFD) and quantified the heat loss differences between hives and the nests honey bees vote for.

Heat retention is important for honey bees as they need to keep the internal temperature of part of their nest above 20°C all year round and part of it close to 34°C for most of the year.

My findings show the tree nests lose substantially less heat than the conventional hives used by researchers. My study also used CFD to visualise the air flows inside both tree and hives, which showed that the internal air circulation within the hive is of substantially different type to that inside the tree nest.

In addition the study has shown that features of man made hives inserted for the beekeeper or researcher’s convenience to easily insert and remove frames actually increase heat losses substantially.

Why has this not been done already?

In the 1930s, all sorts of hive experiments were conducted. By the 1940s, scientists concluded that different hives made little difference to bees. Thus the baseline for research, that hive characteristics could be ignored, was set.

However these experiments did not quantify key physical characteristics (such as heat loss), or determine if the experiments actually changed much physically inside the hive, or measured how man-made hives related to the preferences of honey bees. It was only in the late 1970s that research was carried out into honey bee nest preferences and then later around 2003 into the way honey bees seek out new nest locations and vote for them.

This knowledge about nest preferences and seeking has had little impact on hive based research, probably because the doctrine “hives make no difference” was well established. This means today, as in the 1950s, research does not take into consideration key physical characteristics of the hive nor place them in context with the honey bee preferences that have evolved.

The differences between the hive and the tree nest are so stark, it does call into question whether some research is really about the bees or the bees coping with us.

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Mitchell, Derek (2016) Ratios of colony mass to thermal conductance of tree and man-made nest enclosures of Apis mellifera: implications for survival, clustering, humidity regulation and Varroa destructor. Int J Biometeorol

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In the absence of human intervention, the honeybee (Apis mellifera L.) usually constructs its nest in a tree within a tall, narrow, thick-walled cavity high above the ground (the enclosure); however, most research and apiculture is conducted in the thin-walled, squat wooden enclosures we know as hives. This experimental research, using various hives and thermal models of trees, has found that the heat transfer rate is approximately four to seven times greater in the hives in common use, compared to a typical tree enclosure in winter configuration. This gives a ratio of colony mass to lumped enclosure thermal conductance (MCR) of less than 0.8 kgW(-1) K for wooden hives and greater than 5 kgW(-1) K for tree enclosures. This result for tree enclosures implies higher levels of humidity in the nest, increased survival of smaller colonies and lower Varroa destructor breeding success. Many honeybee behaviours previously thought to be intrinsic may only be a coping mechanism for human intervention; for example, at an MCR of above 2 kgW(-1) K, clustering in a tree enclosure may be an optional, rare, heat conservation behaviour for established colonies, rather than the compulsory, frequent, life-saving behaviour that is in the hives in common use. The implied improved survival in hives with thermal properties of tree nests may help to solve some of the problems honeybees are currently facing in apiculture.

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Derek Mitchell, Honey Bee Cluster—not insulation but stressful heat sink, Journal of the Royal Society Interface (2023). DOI: 10.1098/rsif.2023.0488. royalsocietypublishing.org/doi ... .1098/rsif.2023.0488

The author quoted saying "This new research indicates that rather than being benign, clustering is a survival behavior in response to an existential threat—resulting in increased stress due to cold and exertion. Some honeybees may even eat their own young to survive."

He added, "In anthropomorphic terms, clustering is not a "wrapping of a thick blanket" to keep warm—but more like a desperate struggle to crowd closer to the 'fire' or otherwise die."

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Mitchell D. 2019 Nectar, humidity, honey bees (Apis mellifera) and varroa in summer: a theoretical thermofluid analysis of the fate of water vapour from honey ripening and its implications on the control of Varroa destructor. J. R. Soc. Interface 16: 20190048. http://dx.doi.org/10.1098/rsif.2019.0048

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This theoretical thermofluid analysis investigates the relationships between honey production rate, nectar concentration and the parameters of entrance size, nest thermal conductance, brood nest humidity and the temperatures needed for nectar to honey conversion. It quantifies and shows that nest humidity is positively related to the amount, and water content of the nectar being desiccated into honey and negatively with respect to nest thermal conductance and entrance size. It is highly likely that honeybees, in temperate climates and in their natural home, with much smaller thermal conductance and entrance, can achieve higher humidities more easily and more frequently than in man-made hives. As a consequence, it is possible that Varroa destructor, a parasite implicated in the spread of pathogenic viruses and colony collapse, which loses fecundity at absolute humidities of 4.3 kPa (approx. 30 gm23) and above, is impacted by the more frequent occurrence of higher humidities in these low conductance, small entrance nests. This study provides the theoretical basis for new avenues of research into the control of varroa, via the modification of beekeeping practices to help maintain higher hive humidities.

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Honeybees cluster together when it’s cold – but we’ve been completely wrong about why

Published: November 24, 2023 5.18pm GMT

Author

1. Derek Mitchell

   PhD Candidate in Mechanical Engineering, University of Leeds

Disclosure statement

Derek Mitchell does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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Honeybees in man-made hives may have been suffering the cold unnecessarily for over a century because commercial hive designs are based on erroneous science, my new research shows.

For 119 years, a belief that the way honeybees cluster together gives them a kind of evolutionary insulation has been fundamental for beekeeping practice, hive design and honeybee study. More recently, California beekeepers have even been putting bee colonies into cold storage during summer because they think it is good for brood health.

But my study shows that clustering is a distress behaviour, rather than a benign reaction to falling temperatures. Deliberately inducing clustering by practice or poor hive design may be considered poor welfare or even cruelty, in light of these findings.

Honeybee (Apis mellifera) colonies don’t hibernate. In the wild they overwinter in tree cavities that keep at least some of their numbers above 18°C in a wide range of climates, including -40°C winters. But popular understanding of their overwintering behaviour is dominated by observation of their behaviour in thin (19mm) wooden hives. These man-made hives have very different thermal properties compared with their natural habitat of thick-walled (150mm) tree hollows.

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The walls of commercial hives are thinner than the kind of cavities wild honeybees live in. Derek Mitchell

Getting through winter

On cold days in these thin-walled hives, colonies form dense disks of bees, called a cluster, between the honeycombs. The centre of these disks (the core) is less dense and warmer (up to 18°C). This is where the honeybees produce most of the heat by eating and metabolising the sugar from honey. The cooler outer layers (mantle) produce very little heat as the bees’ body temperatures are too low. If the temperature falls much below 10°C, the bees there will die.

Since 1914, beekeeping texts and academic papers have said the mantle “insulates” the inner core of the hive. This meant beekeepers saw clustering as natural or even necessary. This belief was used in the 1930s to justify keeping honey bees in thin-walled hives even in -30°C climates. This led, in the late 1960s in Canada, to a practice of keeping honeybees in cold storage (4°C) to keep them clustered over the winter.

In the 2020s, keepers are refrigerating honeybees in summer to facilitate the chemical treatment of parasites. This is happening across the US – for example in Idaho, Washington and Southern California. Outside of a cold winter, if beekeepers want to treat mite infestations, they normally have to locate and cage the queen. But cold storage means beekeepers can skip this labour-intensive step, making their commercial pollination services more profitable.

Struggling for warmth

However, my study found cluster mantles act more like a heatsink, decreasing insulation. Clustering is not a wrapping of a thick blanket to keep warm, but more like a desperate struggle to crowd closer to the “fire” or die. The only upside is that the mantle helps keep the bees near the outside alive.

As the temperature outside the hive falls, bees around the mantle go into hypothermic shutdown and stop producing heat. The mantle compresses as the bees try to stay above 10°C.

The mantle bees getting closer together increases the thermal conductivity between them and decreases the insulation. Heat will always try to move from a warmer region to a colder one. The rate of heat flow from the core bees to the mantle bees increases, keeping those bees on the outside of the mantle at 10°C (hopefully).

Think of a down jacket – it’s the air gap between the feathers that help keeps the wearer warm. Honeybee clusters are similar to the action of compressing a down jacket, whereby the thermal conductivity eventually increases to that of a dense solid of feathers, more like a leather jacket.

In contrast, when penguins are huddling in the Antarctic winter, they all keep their body core hot at similar temperatures, and therefore there is little or no heat transfer between the penguins. Unlike the bees in the mantle, there aren’t any penguins in a hypothermic shutdown.

Academics and beekeepers have overlooked the part played by the invisible air gap between the hive and the cluster. The thin wooden walls of commercial hives act as little more than a boundary between the air gap and the outside world. This means that for hive walls to be effective, they have to be substantially insulating, such as 30mm of polystyrene.

This misunderstanding of the complex interaction between the colony enclosure, thermofluids (heat, radiation, water vapour, air) and honeybee behaviour and physiology are a result of people not recognising the hive as the extended phenotype of the honey bee. Other examples of extended phenotype include a spider’s web and a beaver’s dam.

There are almost no ethics standards for insects. But there is growing evidence that insects feel pain. A 2022 study found that bumblebees react to potentially harmful stimuli in a way that is similar to pain responses in humans. We urgently need to change beekeeping practice to reduce the frequency and duration of clustering.

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Seeley, Thomas (2019) The Lives of Bees: The Untold Story of the Honey Bee in the Wild.

So much information in this book!  Please find a copy and enjoy!

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Seeley, Thomas

https://www.youtube.com/watch?v=1zvA7EoMLZA

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Additionally, insulation with a vented top creates even more problems for bees:

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Honey bee engineering: Top ventilation and top entrances

August 2017American Bee Journal 157(8):887-889   Authors:  Derek Mitchell

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The consequence for the honey bees is that any thermal advantage of the insulation can be negated and perhaps even reversed by the addition of a top vent. This high velocity flow through the top vent will move the previously slow or stagnant air (i.e. entrainment) and remove moisture from the internal structures such as larvae (forced evaporation). This not only dries parts of the hive it also cools the hive as evaporation of water needs energy (evaporative cooling). The honey bees now have the added problem of dehydration. Without the top vent, the air would be hot and humid, good for bees. With the top vent, the lower parts of the hive are cold and top parts hot and very low humidity, not good for bees.

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Thermal efficiency extends distance and variety for honey bee foragers: Analysis of the energetics of nectar collection and desiccation by Apis mellifera

• December 2018Journal of The Royal Society Interface 16(150)

DOI:10.1098/rsif.2018.0879

Authors:

 

Derek Mitchell

• University of Leeds

• Excerpt:

 “For bee-keeping it quantifies the summer benefits of a key hive design parameter, hive thermal conductance and gives a sound theoretical basis for improving honey yields, as seen in expanded polystyrene hives.”

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(So many questions answered here:)

sections:

5.2. Humid brood zone, dry nectar honey zone

Honeybees appear on first inspection to have conflicting requirements of a high-temperature humid brood zone and dry air needed for nectar desiccation. If one looks at figure 13, one can see that if the humid air from the brood zone is heated it can desiccate nectar to low moisture levels. If air containing 4.3 kPa of water is then heated to 312 K then it will desiccate nectar to produce honey with only 20% water. This water content is low enough to prevent microbial growth in the honey and the vapour pressure is high enough to hinder the breeding of varroa. This fulfills both the need to have a long-term food supply and to reduce the impact of this parasite.

In this model, these zones are separated; however, for honeybees, this may not be easy to achieve, particularly in low aspect ratio man-made hives, where thermal stratification is not strong and is often disturbed by beekeepers.

5.3. High humidity required, but low humidity found in man-made hives

There is a marked contrast in humidity between in vitro honeybee rearing 4.1 kPa [28] and man- made hives 2.2–3.3 kPa [36,45]. In the latter, the humidity is measured outside the micro climates in the cells maintained by the nurse honeybees. If A. mellifera optimally evolved for tree dwelling then maintaining this difference between the general humidity and the micro climates must therefore represent a stress condition. The difference arises from the condition that unless there are very high water production rates then internal humidity in high conductance, large entrance hives is tied down to {1, TOut} (dew point ∼ outside temperature) and when large top vent/entrances are added then it is tied to {χOut, TOut}

5.4. Hives good for varroa, tree nests good for honey bees

That high humidities particularly in cooler climates require low thermal conductance enclosures has been discussed in relation to varroa in other work [4] and is an accepted thermofluid phenomenon [46]. In addition, the possible impact of top vents or entrances, using recent thermofluid models [47], has also been discussed [48].

The common practice of man-made hives of thin-walled wooden construction with many shallows on top is shown in the high conductance scenarios (limits E, F, G and H) which result in much higher lumped thermal conductances than tree nests (limits A, B, C and D) of 2.5 to 12 WK−1 versus 0.4 to 2.0 WK−1. This and the very much larger entrances used in summer (limits F, H) tie the humidity close to {1, TOut} at low water production rates and increase the water production rate needed to reach 4.3 kPa, by a factor of five as can be seen in figures 11 and 12 (i.e. 50 mg s−1 versus 10 mg s−1).

Taking nectar concentration of 0.33, typical of oil seed rape, a common European honey producing crop, one can see from figures 5 and 7 that these water production rates imply honey production rates of 12–25 mg s−1 for a man-made hive and 1–3 mg s−1 for a tree nest. This means honeybees in man-made hives need to forage and desiccate honey at 10 times the rate to obtain the 4.3 kPa humidity sufficient to affect varroa fecundity. The foraging conditions needed for these honey production rates will occur less frequently than those required by the modest rates needed by tree nests.

Counterintuitively, a subtropical climate, such as Florida, is not sufficient. The common practice of using high conductance, top vented hives [49,50], ties internal humidity to the outside, which in a Florida summer averages at 2.8 kPa {0.72, 301 K} [51]. At low water production levels, in this climate and hives, but without top vents, the humidity will only accumulate to ca 3.8 kPa, allowing varroa to proliferate.

However, with a sustained average outside temperature of above 303.2 K, e.g. warm desert areas of southern Algeria, the analysis shows a high conductance hive, without top vents, can accumulate 4.3 kPa. This may account for the reported higher brood infestation in northern compared to southern Algeria [52] where, in the south, for large parts of the year, the average ambient temperature is above 303.2 K [53]; yet in the north, the average summer temperature is 298 K [21] with a corresponding hive humidity of 3.2 kPa.

In addition, better nectar sources and higher external temperatures, factors shown in this analysis to give higher nest humidity, have been positively correlated with reduced varroa infestation in an experimental research of Mediterranean apiaries [54].

Thus changes to beekeeping practice can improve the frequency of varroa disrupting high humidity for man-made hives: improved foraging, avoiding top vents, constructing hives from lower thermal conductivity materials, having fewer shallows on the hive by more frequent harvesting and matching entrance size to water removal demand by changing the entrance size in response to changing internal humidity or ripening activity.

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Effects of Oxalic Acid on Apis mellifera (Hymenoptera: Apidae)

Eva Rademacher *, Marika Harz and Saskia Schneider

Institute of Biology/Neurobiology, Freie Universität Berlin, Königin-Luise-Str. 28-30, 14195 Berlin, Germany; marika.harz@lwk.nrw.de (M.H.); saskia.schneider@kabelmail.de (S.S.)
* Correspondence:e.rademacher@fu-berlin.de;Tel.:+49-30-8385-6537

Academic Editor: Brian T. Forschler 

Published: 7 August 2017

Abstract:

Oxalic acid dihydrate is used to treat varroosis of Apis mellifera. This study investigates lethal and sublethal effects of oxalic acid dihydrate on individually treated honeybees kept in cages under laboratory conditions as well as the distribution in the colony. After oral application, bee mortality occurred at relatively low concentrations (No Observed Adverse Effect Level (NOAEL) 50 μg/bee; Lowest Observed Adverse Effect Level (LOAEL) 75 μg/bee) compared to the dermal treatment (NOAEL 212.5 μg/bee; LOAEL 250 μg/bee). The dosage used in regular treatment via dermal application (circa 175 μg/bee) is below the LOAEL, referring to mortality derived in the laboratory. However, the treatment with oxalic acid dihydrate caused sublethal effects: This could be demonstrated in an increased responsiveness to water, decreased longevity and a reduction in pH-values in the digestive system and the hemolymph. The shift towards stronger acidity after treatment confirms that damage to the epithelial tissue and organs is likely to be caused by hyperacidity. The distribution of oxalic acid dihydrate within a colony was shown by macro-computed tomography; it was rapid and consistent. The increased density of the individual bee was continuous for at least 14 days after the treatment indicating the presence of oxalic acid dihydrate in the hive even long after a treatment.

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Thymol research:

 

Use of Thymol in Nosema ceranae Control and Health Improvement of Infected Honey Bees

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9319372/

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Nosema ceranae is the most widespread microsporidian species which infects the honey bees of Apis mellifera by causing the weakening of their colonies and a decline in their productive and reproductive capacities. The only registered product for its control is the antibiotic fumagillin; however, in the European Union, there is no formulation registered for use in beekeeping. Thymol (3-hydroxy-p-cymene) is a natural essential-oil ingredient derived from Thymus vulgaris, which has been used in Varroa control for decades. The aim of this study was to investigate the effect of thymol supplementation on the expression of immune-related genes and the parameters of oxidative stress and bee survival, as well as spore loads in bees infected with the microsporidian parasite N. ceranae. The results reveal mostly positive effects of thymol on health (increasing levels of immune-related genes and values of oxidative stress parameters, and decreasing Nosema spore loads) when applied to Nosema-infected bees. Moreover, supplementation with thymol did not induce negative effects in Nosema-infected bees. However, our results indicate that in Nosema-free bees, thymol itself could cause certain disorders (affecting bee survival, decreasing oxidative capacity, and downregulation of some immune-related gene expressions), showing that one should be careful with preventive, uncontrolled, and excessive use of thymol. Thus, further research is needed to reveal the effect of this phytogenic supplement on the immunity of uninfected bees.

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Lethal and sub-lethal effects of thymol on honeybee (Apis mellifera) larvae reared in vitro

 

https://pubmed.ncbi.nlm.nih.gov/23512688/

 

Background: Thymol offers an attractive alternative to synthetic chemicals to keep Varroa under control. However, thymol accumulates in bee products and is suspected of having adverse effects on colonies and especially on larvae. In this study, we investigated the effects of acute and chronic exposure to thymol on larvae reared in vitro with contaminated food and compared results to the theoretical larval exposure based on the amount of pollen and honey consumed by larvae during their development.

Results: The laboratory assays reveal that, first, the 48 h-LD50 of thymol introduced into larval food is 0.044 mg larva(-1) . Second, the 6 day-LC50 is 700 mg kg(-1) food. A significant decrease of larval survival and mass occurred from 500 mg thymol kg(-1) food (P < 0.0001). Finally, vitellogenin expression, which reached a maximum at the fifth instar larvae, is delayed for individuals exposed to 50 mg thymol kg(-1) food (P < 0.0006). That is 10 times higher than the theoretical level of exposure.

Conclusion: Based on the level of thymol residue found in honey and pollen, these results suggest that the contamination of food by thymol represents no notable risk for the early-developing larvae.

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Presence, persistence and distribution of thymol in honeybees and beehive compartments by high resolution mass spectrometry

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https://www.sciencedirect.com/science/article/pii/S2666765721000569

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"The concentration of thymol found during and after the treatment are above the tolerance value of 800 μg/kg, and very close to the taste threshold of 1100 μg/kg during the treatment application. These values indicate that the taste of the honey may be changed."

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More to come!

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