How the Cloudy Wing Virus Affect Honey Bees

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Quick Overview

The Cloudy Wing Virus (CWV) is a lesser-known yet common pathogen in collapsing honey bee colonies, closely associated with the varroa mite, a known parasite and potential vector for the virus. This article delves into the challenges posed by CWV and other viruses to global bee populations, which are critical pollinators in our food production systems.

Diagnosis of CWV involves RNA extraction and RT-PCR amplification from bee samples, but there are no specific treatments for the virus. Management strategies focus on prevention and control, such as destroying severely affected colonies, replacing queens, and destroying infected combs. Good beekeeping practices, including hive cleanliness, comb replacement, and avoiding equipment interchange, are essential. Additionally, boosting the bees’ immune systems with non-pathogenic bacteria and utilizing propolis for its antimicrobial properties can help.

Varroa mite control is a crucial aspect of managing CWV, given the mite’s role as a vector. Varroa mite control strategies include cultural solutions like using resistant bee stocks, mechanical solutions like mite trapping and screened bottom boards, and chemical remedies, both soft (like formic and oxalic acids) and hard chemicals, though the latter are less recommended due to residue concerns.

Despite the prevalence of CWV, especially in Europe, the exact impact of the virus remains unclear due to inconsistent data. However, the association between varroa mite infestations and CWV highlights the importance of comprehensive mite management to prevent viral infections in honey bee colonies.

What is the Cloudy Wing Virus?

The Cloudy Wing Virus is closely linked to the deadly varroa mite parasite and most instances of severe varroa infestations go hand in hand with it. It has therefore been implied that the mite might be a primary vector for the virus, even though this has not yet been clearly demonstrated.

The Cloudy Wing Virus is perhaps one of the least studied viruses in honey bee colonies but is common in collapsing honey bee colonies. You may have come across the graphic example of the extensively publicized economic, social, and political disruption that has been caused by the widespread colony collapses reported by migratory beekeepers within the US. That helps attest to the fact that honey bees face serious challenges and need intervention. Many of the challenges that play a role and can result in the death of bees include parasites, diseases, climatic factors, and exposure to chemicals such as pesticides or insecticides.

The beekeeping industry plays an important role in global food production. Each season, pollination by honeybees and other insects contributes billions to the overall food production in the US and the entire globe. As of October 2019, it was estimated that pollinators directly contribute about $235 to $577 billion US Dollars in value of global food production. In the past few years, beekeepers globally have been complaining of significant bee deaths within their apiaries. This mass mortality of honey bees poses a serious threat to beekeeping and humanity in general. A decline in bee population affects many industries worldwide that rely directly or indirectly on honey bee products and services.

Entry Points for Viruses and Infections

It is almost impossible to escape viruses since they are present in so many forms and pose a serious threat even to humans. Honey bees are not an exception, with most of its viruses being diagnosed through either symptoms or diseases from certain infections.

The close linkage between viruses and honey bee mortality has raised a lot of concern globally, forcing experts to go deeper into their research. At least 18 viruses are known to target honey bees. On top of the list include: Chronic Bee Paralysis Virus (CBPV), Sacbrood Virus (SBV), Deformed Wing Virus (DWV), Black Queen Cell Virus (BQCV), and many others.

Most of these viruses portray apparent clinical symptoms at some point, with laboratory testing proving to be the go-to solution for diagnosis. Things have recently become easier given the fact that nucleotide sequences can now be accessed for most of the honey bee viruses. These have helped develop diagnostic assays that are nucleic acid-based.

Viral Transmission

Honey bee viruses such as the Cloudy Wing Virus can be transmitted through various channels and can take any of two forms: vertical or horizontal transmission.

Vertical transmission

This refers to the establishment of a new infection from one generation to the next. For instance, the queen bee can transmit a virus to the eggs or brood. This can occur either on the egg surface or within the egg. Another example of vertical transmission of a virus is where the virus is present in drone sperm. The infection can move from there to the queen bee.

Horizontal transmission

This refers to the transfer of infection between honey bees of the same generation. This could occur through various ways, which could be body contact or oral transfer. Fecal matter, venereal transmission from drone to queen during mating flights, contaminated food, or vectors can be sources of infections. Vectors are common and they could be mechanical or biological. The mechanical vector transmits the virus without being infected whereas the biological multiplies the virus before transmission.

Diagnosis of the Cloudy Wing Virus

Diagnosis of the Cloudy Wing Virus involves the use of samples collected randomly from honey bee colonies. These are transported on ice at -25 ˚C and kept until use. The next step will be RNA eExtraction of each of the individual honey bees. This is carried out using a pestle and mortar, 1 ml Trizol reagent (Biobasic). The mixture is then transferred into 1.5 ml microfuge tubes.

Chloroform is then used to separate protein fraction from the organic or lower phase. 1 ml of iso-propanol with a centrifugation of 14000 rpm will precipitate the RNA from the aqueous (upper) phase. The nucleic acid pellets that result are washed two times using 70% ethanol and then resuspended in nuclease-free water.

Then follows the RT-PCR Amplification where each RNA sample is analyzed to decipher bee virus sequences. Further tests and analysis are done to ascertain the presence of the virus.

Prevention and Control of the Cloudy Wing Virus

There exist no specific and effective therapeutic remedies for most of the viral diseases that affect honey bees; the Cloudy Wing Virus is no exception. However, there are certain actions that you can take to lessen the impact and spread of the virus.

  • In the case of severe symptoms, all affected colonies should be destroyed. All the combs and bees should be burnt. If you note symptoms are less severe, then replace the queen and remove and destroy all infected honeycombs. All affected beehives should be thoroughly cleaned and disinfected before use. You can disinfect the hives using bleach or by passing a blue flame over the beehives. Infected combs should never be reused.
  • You can also train bees or buy resistant stock of bees. Certain honey bee stocks have developed ways of countering infections and diseases over time. This could be a hygienic behavior that enables the honey bees to respond well to infections or a strong immune system developed over the years.
  • Observe a period of quarantine for newly introduced queens as you monitor the health of the brood. This will help prevent viral transmission via transovarian infection. Remember, viruses can be transferred from the queen bee to the eggs and brood.
  • Adopt good beekeeping practices to keep out diseases and other stress factors. Unhygienic beekeeping practices factors can create a breeding ground for viruses and infections that bring about diseases.  You should keep the beehives clean and well-ventilated. Brood combs should also be replaced yearly and comb transfers between hives avoided. Finally, improve the honey bee’s nutrition and health by supplementing feeding. All supplements should be of good quality and free of contamination.
  • Boost honey bee immune system through the use of nonpathogenic bacteria. This will help the bees to develop anti-bacterial peptides that boost honey bee immunity. This can be introduced to all life stages of the honey bee so that it can instinctively develop resistance to infections.
  • Consider utilizing propolis since it contains phenolic compounds that are basically essential oils. These boast antimicrobial compounds that inhibit bacterial and fungal activity. Bees can be encouraged to deposit propolis within the hive by using a cotton cloth as the inner board. The interior part of wooded parts of the hive can also be scrapped off to make them rough so that bees can accumulate propolis on these surfaces.
  • Radiation has been used to sterilize wax and honey with no harmful effects reported. The process may however affect the physical and chemical composition of honey. These include reduced enzymatic activities and alteration of color. It also helps sterilize contaminated equipment thus keeping off viruses and other pathogens.
  • Control varroa mites since they act as vectors for cloudy wing virus and other viral infections in honey bees.

Preventing the Cloudy Wing Virus Through Varroa Mite Control

Cloudy Wing Virus - Varroa Mite in Brood

Varroa mites are the most prevalent of all parasites in honey bees. They were introduced in the US in 1987 and have since then been a serious to apiaries globally. The female varroa mite usually lays her eggs inside drone and worker bee cells. However, varroa offspring are predominantly raised in drone cells given the fact that drone cells are bigger, and have a longer cycle when compared to worker cells. This makes it possible for the mites to populate faster per cycle.

Varroa mite control measures include the following:

1. Cultural Solutions

Cultural solutions are aimed at minimizing pest reproduction. These remedies work perfectly when used to control varroa mites. One of the measures is the use of resistant stock such as the Russian honey bee. These stocks of bees have developed some resistance to the mite. Other stocks of bees have instinctively developed parasite control techniques such as hygiene and ankle or leg biting and chewing.

The second approach is the use of small cell combs. These are commercially produced foundations with small hexagons. These small-sized cells have shorter post-capping periods making it difficult for the mites to thrive.

Finally, a brood break which could mean removing the queen for at least 3 weeks can help reduce varroa mites. The caging of the queen can also serve the same purpose. During this time all surviving mites will be forced to move from hatched brood to adult bees. They can then be controlled from there.

2. Mechanical Solutions

Mechanical approaches can work well when used in combination with other varroa mite control measures. It involves hive or colony manipulation.

One of these is mite trapping. This strategy takes advantage of the fact that varroa mites have a preference for drone cells that take much longer post-capping. A drone comb is introduced as a trap to the honey bee colony. This comb is then removed, just before the young drone bees emerge, cutting short the life of most of the developing mites.

A second mechanical strategy is the use of a screened bottom board. This helps eliminate varroa mites through natural fall from the beehive. These mites are unable to climb back to the hive and are thus eliminated. This not only cuts short the mite population but also makes it difficult for the mites to procreate within the beehive.

A final remedy is powdered sugar that is applied to honey bees. This helps stimulate grooming in the bees, leading to fallen mites under the beehive or on the solid bottom board. The method is not effective on its own but it requires other approaches as backup.

3. Chemical Remedies

The use of hard chemicals to control mites is discouraged by some in beekeeping. Soft chemicals are more recommended, even though they should be used in moderation. The soft chemicals are derived from natural products and do leave behind residues. Some of these include formic acid, a chemical that is generated naturally in bee venom and is a major component of honey. The chemical kills the mites and can easily penetrate wax cappings. It should however not be applied under high temperatures (above 85 °F / 29.4 °C).

Oxalic acid is another soft chemical that aids in the control of varroa mites in honey bees. It is an extract derived from plants such as kale, spinach, rhubarb, and beets. It can be applied either as vapor or dribble. Oxalic acid is highly recommended for use during broodless months since it does not penetrate cappings. The ideal period to apply is during early spring and winter. It should however be used in moderation since it can harm bees when used in excess.

Thymol is yet another natural chemical extracted from plants. It is the most popular among beekeepers and takes many forms. It however does not penetrate capped cells just like oxalic acid. Its efficacy is quite low and should therefore be used alongside other varroa mite control measures.

Finally, there are the hops beta acids extracted from the hops plant. These contain potassium salts that are safe for use in honey bee colonies. The chemicals can be applied at any time of the year but preference is given to periods of low brood since it does not infiltrate cell cappings. It is neither affected by high temperatures nor affected by cold conditions.

4. Hard Chemicals

These are synthetic chemicals that have been formulated for varroa mite control. They are rarely recommended since they have a residual effect on honey bee colonies. These are mainly acaricides and miticides that target the mites. The chemicals are 95% effective in the control of mites and are ideal only in severe cases of infestation.

Coumaphos and fluvalinate were popular in the past but these have since been abandoned since honey bees have developed some resistance to these chemicals. It has also been pointed out that the chemical residue persists and builds up in wax posing a serious risk to both the beekeeper and honey bees.

Amitraz is ideally a hard chemical that appears to be accepted as the best remedy for varroa mite infestation in honey bees. It is sold under various brand names, one of them being Apivar. It does not leave behind some residues and will not contaminate wax or honey. Unfortunately, excessive usage of Amitraz may be harmful to honey bees. Mites can also develop some resistance if the chemical is overused.

Geographical Distribution of the Cloudy Wing Virus

The Cloudy Wing Virus is widely distributed throughout Europe. The virus has also been detected in other continents. It was detected serologically in Britain, from extracts of dead bees that had been collected from approximately 15% of colonies. The number kept fluctuating significantly during the year, without any apparent seasonal cycle of the viral incidence. Other studies carried out in England showed pathogen incidence for honey bee colonies with varroa mites but soon showed that the virus was more widespread in varroa-infested colonies when compared to mite-free colonies in Britain.

During most of these studies, the Cloudy Wing Virus was detected through serology in a huge percentage of the dead adult bees throughout the season, and during the summer for honey bee pupae. Initially, it appeared the feeding activities of the varroa mites played a key role in the transmission of CWV since it was detected in both infested pupae and individual varroa mites. However, later observations proved otherwise. The virus occurrence appeared to be independent of the level of mite infestation.

In similar studies carried out in Nordic countries, that is, Denmark, Sweden, Finland, and Norway different results were noted however. The Cloudy Wing Virus appeared to be the most prevalent in apiaries despite the level of varroa mite infestation. Furthermore, this high prevalence did not have any correlation with colony collapse.


There is little information currently available that can explain the persistence and spread of the Cloudy Wing Virus, whether in nature or field data. Therefore, the actual effect of this honey bee virus is lacking. Nonetheless, the occurrence and prevalence of the virus in both adult bees and brood is not a common occurrence and the prevalence of this infection in both brood and adult bees suggests that it is not exceedingly pathogenic. The virus is however fatal and can lead to death in honey bee colonies. Infected honey bees tend to be inactive and will die a few days later.

The symptoms of the Cloudy Wing Virus are not reliable for diagnosis and its close linkage to varroa mites is yet to be substantiated. The various laboratory tests done in the past do not give consistent results when it comes to demonstrating the correlation between varroa mite infestation and cloudy wing virus. That notwithstanding, it is still of sentimental importance to manage the mites as a measure of countering viral infestation in the honey bees. Other control measures such as cultural, mechanical, or chemical solutions will also help control viral infections in honey bee colonies.



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About Michael Simmonds

Michael Simmonds is an American beekeeper with more than two decades of experience in beekeeping. His journey with bees began in his youth, sparking a lifelong passion that led him to start his own apiary at the tender age of 15. Throughout the years, Simmonds has refined his beekeeping skills and has accumulated a wealth of knowledge concerning honeybee biology and behavior. Simmonds' early exposure to beekeeping ignited a fascination with these pollinators, influencing his decision to establish BeeKeepClub in 2016. The website was created with the aim to serve as the ultimate resource for beginners interested in beekeeping. Under Simmonds' guidance, BeeKeepClub provides comprehensive information to novices, including the basics of beekeeping, the different types of bees and hives, the selection of hive locations, and the necessary beekeeping equipment. In addition, the site offers detailed reviews of beekeeping tools to help enthusiasts make informed decisions and get the best value for their investment​​. His contributions to the beekeeping community through BeeKeepClub are substantial, offering both educational content and practical advice. The website covers a wide array of topics, from starting an apiary to harvesting honey, all reflecting Simmonds' extensive experience and passion for the field. Simmonds’ approach is hands-on and educational, focusing on the importance of understanding bees and the environment in which they thrive. His work not only guides beginners through their beekeeping journey but also reflects a commitment to the well-being of bees. Michael Simmonds has dedicated a significant part of his life to bees and beekeeping, and through BeeKeepClub, he has made this knowledge accessible to a broader audience. His work undoubtedly embodies a blend of expertise, authority, and trustworthiness in the realm of beekeeping.
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