Why do Bees Make Propolis?

Honeybees are experts at collecting plant resins and turning them into propolis. But what is it that makes propolis so special? Why is propolis so important for honeybees, and what do they do with it?

Uses of propolis within the hive

While we may think of propolis just in terms of bee glue, it has in fact many uses within the hive.

• Coating the inside of the hive with propolis makes surfaces smooth to aid comb attachment in wild colonies.
• Propolis has waterproofing abilities which help control and regulate the internal environment of the hive.
• Bees use propolis to seal gaps and manage ventilation and airflow.
• Propolis is used to narrow hive entrances.
• Using propolis, bees encapsulate, trap and corral pests and intruders.
• Propolis plays an important role in the colony immune system by creating an environment unfavourable for microbial growth.

To read more about propolis, what it is and how bees make it click here: What is Propolis?

Wild colonies and propolis envelope

In the wild, the inside of a honeybee nest is not smooth as the planed timber that make up the insides of our man-made hives. It is much rougher and provides the bees with plenty of surfaces and crevices to deposit resins and create what is called a propolis envelope. The entrance to the hive often also has a thick veil or curtain of propolis.

Although our hives are often not conducive to a propolis envelope, this does not seem to lessen the bees’ need to collect and deposit propolis within the hive. Hence, we often find layers or blobs of propolis in corners and crevices. We also find it between frames, on and under the lugs of the frames, on frame runners as well as between boxes, on queen excluders, vents etc. Some colonies are zealous resin gatherers and propolis producers. Propolis gathering and producing is a genetic trait, which can make bee handling and inspections sticky and tricky.

Propolis and bee health

There is a lot of very exciting research going on around propolis and its impacts on honeybee health. Much research has been done, and as is often the case, has led to new questions and hypotheses that need further research. Notwithstanding that, here are a few things we do know:

• Propolis is an integral part of the honeybees’ immune defence or social immune system.
• A propolis envelope helps to protect honeybee colonies (and their brood) from harmful pathogens (bacterial, fungal, and viral).
• Individual bees in propolis-rich colonies produce less immune responses than those in propolis-poor colonies.
• Brood food produced in propolis-rich colonies has higher antimicrobial activity than brood food produced in propolis-poor colonies.
• Brood viability in propolis-rich colonies is higher than in propolis-poor colonies, leading to larger populations and impacts positively on productivity.
• Honeybees self-medicate with propolis if exposed to some pathogens.
• Resin foraging increases in colonies that are exposed to certain pathogens.
• Propolis is essential for the health and resilience of the bee and is something that we as beekeepers should embrace and encourage.

The immune system and Propolis

Propolis contributes favourably to both the immune response of individual honeybees and the social immunity in honeybee colonies. It is essential in maintaining healthy colonies as well as in fighting disease. In discussing this further, I will use terms such as propolis-rich and propolis-poor. Propolis-rich refer to colonies that have either been encouraged to develop a propolis envelope or where the interior of the hive has been enhanced with propolis. When we talk about immune responses, this refers to individual bees, and social immunity to the whole colony.

Honeybees use propolis to create a colony-wide immune system. By coating the inside of the hive with this highly anti-microbial substance, they ensure that the nest environment is reasonably stable, or homeostatic. Hence, it provides unfavourable conditions for fungal, viral, and bacterial pathogens to multiply. Consequently, the bees have designed a health care system where the first line of defence against pathogens is a social immune system. This social immune system puts a lot less pressure on bees and their individual immune responses.

Propolis lessen individual immune responses

Experiments have shown that young bees from propolis-rich colonies produce less immune responses (activation of two immune-related genes, Hymenoptaecin and AmEater) than young bees from propolis-poor colonies. It is also proven that the lessening in immune responses is due to reduced pathogen loads in the hive. The lessening is not as a result of immune suppression by propolis. Although gathering resin is hard work for bees, creating a propolis envelope is a cost-effective way of ensuring the health and productivity of a colony.

When individual bees have less expression of immune responses, they conserve energy for other tasks. Such as looking after brood, housekeeping duties, foraging, etc. This, coupled with the fact that propolis-rich colonies also have higher brood viability and longer lifespan of bees, means stronger colonies and more foragers. This, in turn, leads to more resin collectors and a potential for higher honey yield. It has been a common misconception that colonies that collect a lot of resin do so at the expense of honey production. Research has in fact concluded that there is a positive correlation between propolis production and honey production.

Furthermore, propolis stimulates and stabilizes beneficial microbiome in the mouth and stomach of bees.

Viability of brood and longevity

In propolis-rich colonies, there is a higher presence of antimicrobial substances in the brood food compared to brood food from propolis-poor colonies. It is uncertain how these substances get into the brood food. They may be added by the bees or it ends up there due to its high volatility. Brood food is fed to larvae before cells are sealed and they enter the pupa stage in their development. There is a positive correlation between the presence of high inhibitory activity in the brood food and brood viability. Experiments have shown that the viability of brood can be up to 50% higher in propolis-rich colonies than in propolis poor-colonies. 

There has been some research into the longevity of bees and its connection to propolis. Although it is not clearly understood why, scientists have concluded that bees in propolis-rich hives live significantly longer (6.6%) than those in propolis-poor hives. They do this regardless of their genetic disposition towards resin collection. This leads to stronger colonies and more foragers. And this, in turn, has a positive impact on both honey yields and colony health.

Worker bee foraging for propolis on a disused queen-excluder

Propolis and fighting disease

Propolis contains anti-microbial peptides that help the immune system fight off microbes (i.e., fungal, viral, and bacterial pathogens). It also has antimicrobial properties against American Foulbrood (Paenibacillus larvae), Chalkbrood (Ascosphaera apis), and Nosema (N. ceranae). Although the presence of propolis does not seem to impact majorly on Varroa, it does have antiviral effects against Deformed wing virus which Varroa is a vector of. Little is known about its potential effectiveness in combatting European Foulbrood (Melissococcus plutonius).

Several studies have been carried out where different pathogens have been introduced to healthy colonies in propolis-rich and propolis-poor hives. In these colonies, the effect and spread of the disease has been recorded, analysed, and compared. The first study involved chalkbrood. It concluded that colonies without a propolis envelope had more than six times the amount of chalkbrood mummies than those with a propolis envelope. The presence of propolis did not cure the infection, but significantly lowered the amount of disease.

Propolis and American Foulbrood

Similarly positive results were found when American Foulbrood was introduced to colonies with and without a propolis envelope. American Foulbrood is a bacterial disease which affects honeybee larva. When propolis-rich colonies developed symptoms of American Foulbrood, researchers found that the levels of inhibitory activity against American Foulbrood increased in the brood food. Thus, the bees in those colonies were protecting or attempting to protect larva from infection. This is very strong evidence that honeybees not only use propolis to maintain homeostasis when healthy. They also use propolis to self-medicate when under pathogen stress.

Propolis and Varroa

Research has found that resin collection increases when colonies are introduced to certain stresses, but not all. Despite the fact that propolis appears to have negligible effects on Varroa, studies have shown that colonies with a high Varroa load will increase their resin foraging. The hypothesis is that colonies are attempting to combat the diseases and viruses that follow as a result of Varroa. Resin collection also increases when colonies are exposed to fungal diseases such as Chalkbrood. But perhaps surprisingly not considerably when exposed to bacterial infections such as American Foulbrood. Scientists are puzzled by this as it is proven that a propolis envelope has a substantial mitigating effect on American Foulbrood infections in colonies.

Propolis collection is a genetic trait

Finally, it is important to note that resin collection and propolis production is a genetic trait. Instead of breeding this out of our bees as has been done in the past, we should breed for propolis. By breeding from colonies with a propensity for gathering resin, we are also breeding healthier bees and stronger and more resilient colonies. Our job as beekeepers should be to help our bees help themselves. One of the best ways we can do that is by embracing propolis and encouraging the creation of that amazingly beneficial propolis envelope.

Our bees might be small, but they are very resilient. Let’s help them keep it that way!

I hope you enjoyed reading this short article. For more on propolis, please see the following Blogs:

What is Propolis?

Health benefits of Propolis

How to Use Propolis

How to Make Propolis Tincture

You can also purchase Irish Propolis Tincture in our online shop.

Hanna Bäckmo

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