Honeybees’ Natural Defenses Against Threats

Honeybees have lived and thrived in their feral environment long before man thought of domesticating them. The honeybee colony is self-sustaining and can survive without the beekeeper’s help. Bees instinctively use some defense mechanisms to safeguard the colony’s health. These include the elimination of sickened larvae, bees, or pupae. All these and other mechanisms are a part of what is used by bees to secure the honeybee colony from pests, parasites, and diseases. Honeybee colonies rely heavily on a group effort to promote productivity and survival. The colony’s defense against pathogens and parasites is not solely pegged on individual effort but rather on the entire colony. In this article, we’ll discuss honeybees’ natural defenses against pests and parasites.

Effects of Pests, Parasites, and Diseases on Honeybees

Pests, parasites, and diseases can have a serious effect on honeybee colonies. Some of its major effects include:

1. Effect on Mobility

Parasites affect the honeybee’s central nervous system which in turn impairs their motor behavior. Consequently, the restrained host provides a favorable environment for the reproduction and spread of the parasites.

2. Effect on Designation of Work and Transition

Honeybees are experts when it comes to the segregation of duties within the colony. The bees begin to specialize in tasks from an early age and this helps with hive organization. Unfortunately, parasites and pathogens affect behavior and cognition in honeybees making it difficult for bees to undertake their tasks or transition to other roles.

The first stage in honeybees is the in-hive activities that primarily include the nursing of the brood and queen. This is followed by the foraging stage with the mainly responsible bees being the middle-aged and adult bees. This transition from in-hive activities to foraging requires the brain to mature and prepare the bees for it.

The behavior change in bees will occur from 12 to 15 days from the emergence of the young bees. It is controlled by two hormones, namely the juvenile and vitellogenin hormones. The vitellogenin will decrease as the juvenile hormone increases for the transition to occur.

Foraging behavior will be affected for a number of reasons. The decline in food resources, a lower number of foragers, or parasite infestation will trigger foraging behavior in younger bees. The microsporidian N. ceranae is an example of a parasite that will cause foraging in younger bees since it greatly cripples the forager population in the hive.

Another effect associated with pests and parasites is the effect they have on the spatial cognitive ability of foragers. Those affected tend to perform poorly due to immature brains and poor foraging ability. This affects the colony’s food reserves, forcing younger bees to begin foraging.

3. Alters Social Interactions

Pathogens and parasites affect social interactions in the honeybee colony. Bees rely on social interactions for their survival and hence any impairment can have a negative impact on their well-being. For instance, honeybees infected with microsporidian N. ceranae exhibit crippled trophallaxis (the process of exchanging food from mouth to mouth in bees).

This is attributable to the increased appetite in infected members and the least likelihood of sharing food. Another pathogen is the Kakugo virus which triggers aggressive behavior in guard bees.

4. Effect on Memory and Learning

Honeybees survive based on their ability to learn and remember. Each role of the honeybee colony requires a level of intelligence and memory. For instance, foraging bees need to locate and recognize flowers. They also have to navigate back to the nest with the help of their memory, and visual and olfactory learning.

Parasites impair the honeybee’s visual, olfactory, and memory abilities. Examples of these include the microsporidian parasite N. ceranae which affects the honeybee’s response to odor. The parasite also affects the navigation ability of the honeybees. Foragers that are infected find it hard to locate the hive on their way back. Varroa mites also impair the honeybee orientation and homing rates.

The bee’s visuospatial learning is required when seeking nectar and pollen and this is impaired by pathogens and parasites. The bees need to learn to decipher flowers based on their color and if impaired it becomes a challenge for the bees to find ideal foraging plants.  

Impaired spatial learning is also associated with pathogens and parasites. For instance, the microsporidian N. ceranae affects the ability of worker bees to learn about their surroundings. This spatial learning is required during future foraging activities. Those infected tend to exhibit an impaired desire to venture out, thereby covering reduced areas.

5. Effect on Foraging Activity

Pathogens and parasites have a direct impact on flight and foraging ability in bees. An example of this is the microsporidia Nosema spp that impairs foraging behavior in honeybees. The infected worker bees show a reduced foraging performance compared to the uninfected. The infected also take shorter and interrupted flights as compared to healthy bees.

Microsporidia Nosema spp-infected honeybees have also been found to exhibit the behavior of spending more time outside of the hive. Those infected with the Deformed Wing Virus take shorter flights and spend the least time foraging. The flight and foraging impairment caused by these viruses is attributable to the energy stress the infected experiences. The pathogens and parasites suck out the host resources making it impossible for them to perform normal tasks.

Honeybees that are infected with N Ceranae lack trehalose in their hemolymph which in turn affects their ability to produce Adenosine triphosphate (ATP), an important substance required for flight. The flying ability is therefore impaired.

Honeybees’ Natural Defenses Against Pests and Parasites

Honeybees have developed some natural ways of responding to pests, parasites, and diseases. The behavior is common in both feral and domesticated bees. These include:

1. Honeybees’ Natural Defenses Against Microbes

Honeybees have developed a strong defense against microbes through the production of specific compounds that counter microbial activity. Honeybees have over the years, adapted to producing compounds that help the colony fight pathogens and parasites.

An example of a compound found in honeybees is the venom peptides found on the cuticle. This compound boasts anti-microbial properties and helps the bees fight pathogens. The substance is also found on honeycombs suggesting the worker bees deposit it to keep off pathogens from the combs.

Another compound produced by bees that help counter harmful microbes includes anti-microbial peptides such as Defensin-1. Additionally, the glucose oxidase found in honey and larval diet is a potent anti-microbial compound that helps honeybee colonies boost their defenses against microbes that cause infections.

The honeybee secretions are usually passed through trophallaxis, also called bee-to-bee oral transfer. Though this helps foster pathogen resistance, it can also spread diseases in honeybees.

2. Collection of Plant Compounds

Honeybees also collect plant compounds that help secure the colony from microbes. This helps minimize the energy expended in producing anti-microbial compounds, a process that hugely depends on genetics.

Honeybees rely on plants for anti-microbial compounds such as resins. These substances are harvested from woody shrubs and certain trees. These are used by plants for sealing wounds and protecting delicate leaf buds from pests and pathogens. The honeybees understand the importance of these resins and will collect them for use in the honeybee colony.

One of the ways plant resins are used in the colony is when it is mixed with wax to make propolis, a product that plays an important role in beehive architecture. This is particularly apparent with feral bees, where propolis is used to cover the interior of the tree cavity where their colony has been established. Domesticated honeybees also utilize propolis in various parts of the hive but with a greater portion of it at the entrance. The deposit of propolis at the hive entrance serves as a barrier for keeping out intruders. It also helps disinfect the incoming forager bees before they enter the hive. Propolis is also harvested by humans for use in making drugs.

A higher concentration of resin in honeybee colonies helps eliminate microbes which in turn helps the bees save the energy that would have been exhausted in fighting the microbes. Instead, the energy is focused on engaging in other productive tasks that help boost the colony’s productivity.

Propolis is also considered the best defense against microbes that target broods. These include pathogens that cause American foulbrood and chalkbrood. Additionally, there is a strong link between increased resin collection and resistance to Varroa mites. Colonies that have strong defenses against the Varroa mites have been found to accumulate more plant-based resins. Such colonies exhibit bees with longer lifespans and produce more brood.

The collection of resin is a natural strategy that honeybees use to protect the colony from microbes and other disease-spreading organisms. The bees also use propolis to seal larger pests such as rats that have died inside the hive. This helps prevent microbes from multiplying and spreading to colony members.

It is also worth mentioning that nectar also contains antimicrobial compounds, referred to as metabolites. These are collected by foraging worker bees and play a key role in protecting the honeybee colony from microbes. The substances are mixed with honey and since nectar is sourced from different plants, the final product is rich in diverse anti-microbial compounds. This helps the colony with disease resistance.

3. Natural Selection through Mating Flights

Honeybee colonies have a single queen bee that is the mother of all bees in the colony. She is responsible for guaranteeing genetic diversity in the colony during the mating flights since hundreds of male bees/drones pursue her but only 10 to 35 of these will successfully mate with her. Various benefits are associated with the queen mating with many different male bees.

First off, the number of male bees that mate with the queen bee will affect the number of genetic lineage or subfamilies that will exist in the honeybee colony. This directly affects the genetic diversity within the honeybee colony. Queen bees that mate with more males bring in greater diversity in the genetic makeup within the colony.

Secondly, the mating flights serve as a way of naturally selecting the best male bees that will mate with the female. The few that manage to pursue and capture the queen bee during the flight are not only the fastest but also likely to have stronger genetic makeup. This serves to ensure the future generation of bees are in better health and have greater chances of survival.

Unfortunately, the queen bee mates only once in her lifetime and that only means that she is unable to alter the genetic makeup of her offspring once the mating flight is completed. Subsequent queens, however, will be able to bring in a different genetic diversity.

The importance of genetic diversification in the honeybee colony cannot be emphasized enough and this plays an important role in terms of helping the honeybee colony’s productivity and ability to deter pests, parasites, and diseases. Among these benefits include:

• The foraging efficiency is higher among honeybee colonies that have a higher level of genetic diversity. That means the colony is well-fed and can defend itself. Such colonies exhibit the following traits:
  • Healthy guts to counter negative microbial activity.
  • More productive with increased fitness.
  • High resistance to infections and diseases. This is attributable to higher immunity in larvae and adult bees.
  • An ability to counter different strains of a particular pathogen.

The honeybees intentionally raise future queens from the youngest larvae. This in turn results in bigger queens that mate with more males. These queens are also more productive and will bring in a diverse genetic makeup within the colony. The beekeeper can help support the queen bee through strategic positioning of apiaries in areas with adequate drone sources. This will allow the queen bee to have access to a wide diversity of drones during the mating flight.

4. Specialization/Segregation of Duties

Worker bees are responsible for handling all the tasks in the colony. To achieve maximum efficiency without compromising the colony’s health, the workers have devised task segregation or specialization. This helps the colony to fight parasites and pathogens that target the honeybee colony and this is one of their natural defenses.

The youngest worker bee is responsible for handling cleaning tasks and that involves cleaning cells. As they grow they progress to nursing the queen bee and the young brood. They will then move to maintenance tasks, house workers that receive nectar than pollen and nectar foraging.

Young worker bees handle simple tasks that are within the confines of the honeybee colony for a reason. They are at greater risk and are therefore safer from parasites and diseases within the colony. Additionally, worker bees that have transitioned to foraging tasks are cautious enough to avoid direct contact with younger bees. This helps ensure their safety.

Additionally, the adult bees responsible for removing dead bees and unwanted material from the hive are allowed to come close to the young bees. These tend to be middle-aged bees that are in transition to being foragers and will stay on the edges in most cases to minimize contact with the high-risk younger bees.

The individual interaction and segregation of labor in honeybee colonies help minimize pathogen transmission. The queen, in particular, is safeguarded from coming into contact with high-risk worker bees and this helps limit parasite and disease spread in the colony.

5. Grooming Behavior in Honeybees

Honeybees use grooming as their first line of defense against pests, parasites, and diseases. This is a natural defense method that takes two forms: self-grooming and group grooming.

Grooming helps honeybees to remove harmful parasites such as mites. These include the common Varroa mites and Tracheal mites. Grooming helps prevent individual infection for tracheal mites which ultimately helps eliminate the mites in the colony.

The honeybees use grooming as the natural response and damage to the common Varroa mites. These are brushed off the body and killed. Those that drop off through screened bottom boards are unable to climb back and hence die from exposure to the elements.

Grooming in bees also helps improve the health of sickened colony members. The elimination of pathogens with the help of colony members helps minimize their exposure which consequently boosts individual immune systems or defenses against future exposure. Moreover, honeybees have been found to increase grooming in honeybees that are susceptible to microbes or those with weaker immunity. 

6. Colony Hygiene

Hygienic behavior in honeybees is a natural way of securing the colony from its various pests, parasites, and diseases. This in simple terms refers to the methods the colony uses to ensure the colony is free from infections, which includes detection and removal of infected brood in the honeybee colony.

Strong honeybee colonies exhibit rapid hygienic behavior where the worker bees can detect and remove diseased or paralyzed pupae and larvae. Through this, the sickened brood is eliminated before they reach the infectious stage. This also helps dispose of the parasite or pathogen alongside the infected brood.

Hygienic behavior takes three forms, namely, the detection, uncapping, and removal of the infected brood. Certain honeybee colonies, especially those with poor hygienic behavior, show only two of these forms of hygiene, whereas the successful ones portray all three forms. The latter tend to constantly inspect their cells and will in most cases remove infected larvae and pupae within 24 hours.

Interestingly, some honeybee strains engage in almost none of the three forms of hygienic behaviors. However, the European honeybee exhibits this behavior in all its races. Colonies that have been found to carry out routine hygiene demonstrate high resistance to fungal and bacterial diseases.

Colony hygiene has also been linked with Varroa mite prevalence in honeybee colonies in what is referred to as Varroa Sensitive Hygiene (VSH). This involves measuring the proportion of the mite-infested pupae that are removed by the worker bees. The outcome of the investigation revealed colonies with higher VSH had the lowest mite population over the season. The VSH behavior has been found in the various races of the Western honeybee and is particularly been identified as the reason behind the Varroa mite resistance in the Russian honeybee.

Besides brood removal, another aspect of colony hygiene is the removal of adult honey bees that are parasitized or sick. This has been noted where infested or sickened adult bees leave the colony on their own and never come back. The symptomatic adult bees are also removed from the colony by the bees that perform hygiene roles.

7. Social Fever

This is a natural response that helps honeybees fight various diseases and infections in the colony. The bees will alter the hive temperature to counter symptoms of various diseases. One example of this is the response to chalkbrood disease. The worker bees have been noted to increase the temperature within the brood nest as a way of countering the development of chalkbrood symptoms in the larvae.

The presence of chalkbrood spores triggers the response of temperature increase in the brood nest.  There could also be associated environmental conditions that cause the fever response in honeybees.

8. Abandoning the Hive/Absconding

This is a final response to a dire situation within the honeybee colony. This means the entire colony will move away from the infected beehive to start a new life in a disease and pest-free hive. The bees will leave behind the brood and food stores and seek a new place to build their home.

The absconding behavior is least common in European honeybees compared to their Asian and African counterparts, where this is a common occurrence. Nonetheless, the prevalence of pests, pathogens, and parasites will trigger the behavior in the European honeybee. This is effective in dealing with disease spread within a colony.

Conclusion

Honeybees use the above methods to counter pests, parasites, and diseases in the colony. Nonetheless, the beekeeper has to support the bees when possible. Some of the recommended ways to do this include: ensuring the colony is well-fed, choosing and breeding healthy bee colonies or those known for strong defenses, naturally raising the bees by avoiding chemicals and raising the right colony size. All that ensures the honeybee colony is well-equipped in defending itself from the various pests, parasites, and diseases.