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Simplified field methods for diagnosing honey bee diseases and GBPs to prevent them

Dear TECA members,

My name is Giovanni Formato. I am a veterinarian working as Head of the Beekeeping Laboratory, at the Honey Bee Health laboratory of IZSLT (Istituto Zooprofilattico Sperimentale of Latium and Tuscany, a Governmental Regional Institute for Animal Diseases) (Italy). My area of work is mainly linked to the beekeeping sector with a particular focus on honey bee diseases' diagnosis and management. Since January 2017 I’m the scientific coordinator of the EU project “New indicators and on-farm practices to improve honeybee health in the Aethina tumida era in Europe”. This project is focused on a "new approach" to the Good Beekeeping Practices (GBPs), expecially on those practices able to detect the main honey bee diseases before they become "clinically evident" e.g. using debris (or other matrixes) to detect American Foolbrood (AFB), European Foolbrood (EFB) or Small hive beetle (SHB). For this reason we invented the term "pre-clinic indicator", wth the final goal to reduce the impact of the diseases on the colonies and to reduce the impact of veterinary medicines on the hive products.

Finally, I’m President of SVETAP, that is a Scientific Society of Veterinarians specialized in Apiculture.

In 2015, we moderated the TECA discussion on “Veterinary medicines in beekeeping around the world: Which active ingredients are in use and do they respond to the needs of beekeepers?”, in collaboration with APIMONDIA. Moreover, along with the TECA discussion we conducted a survey with the title “Veterinary medicines in beekeeping around the world” which allowed us to have more data about the challenges that beekeepers face in dealing with disease management and control. In particular, the survey showed that some diseases are very well known by beekeepers worldwide but their impact on honey bee colonies is missing/underestimates and there is a lack of knowledge on the instruments available for diagnosis.

We would like to invite you to actively participate in the upcoming discussion on “Simplified field methods for diagnosing honey bee diseases and GBPs to prevent them”. The purpose of this discussion is to list and suggest the best on-field methods to diagnose honey bee diseases worldwide and to underdstand if they are sufficiently accurate. We also want to look at the available procedures/kits/instruments that can be used in the field to detect and monitor all the honey bee pathogens, before or after clinical symptoms appear. We will also talk about the kind of assistance beekeepers can receive in their respective countries (beekeeper self-diagnosis, expert beekeepers, researchers, governmental inspector) and suggest some GBPs to prevent or avoid the bee diseases in order to assist veterinary services or beekeepers where diagnostic tools/kits are unavailable.

Eran Raizman, Head of the Emergency Prevention System for Animal Health in FAO HQ in Rome, which deals with control of economically important diseases that also cross border such as Avian Influenza and food and mouth disease, will be closely following the discussion.  Eran and his team are convinced that they have a lot to contribute to the apiculture sector in improving diseases control and as a consequence people’s livelihoods and food security.  The Emergency Prevention System for Animal Health team is looking forward to working with beekeepers to improve their own source of livelihoods!

This discussion will last for 5 weeks starting from July 6th to August 8th and will be summarized at the end.

It will be divided into five sections answering the following questions:

A.      From July 6th to July 11th: Which are the GBPs able to prevent diseases or avoid their spreading? Comments on results of the 2015-2016 survey on “Veterinary medicines in beekeeping around the world”: beekeepers knowledge and needs. Which are the most known diseases? Is their impact on colonies underestimated?

B.      From July 12th to July 18th: Main tools available on the field to diagnose Varroa destructor and viruses will be described. Moreover, participants will be asked share the methods they adopt. Are they specific? Is it possible to find a practical and valid method to be used by beekeepers without a laboratory?

C.      From July 19th to July 30th: Main tools available on the field to diagnose American Foulbrood (AFB) and European Foulbrood (EFB) will be described. Participants wil be invited to share the methods they adopt to diagnose AFB and EFB. Are they specific? Is it possible to find a practical and valid method to be used by beekeepers without a laboratory?

D.     From July 31st to August 6th: Main tools available on field to diagnose Nosema and chalkbrood will be described. Again, participants will have the opportunity to share the methods they adopt to diagnose Nosema and chalkbrook. Are they specific? Is it possible to find a practical and valid method to be used by beekeepers without a laboratory?

E.      From to August 7th  to August 14th: Main on-field tools available to diagnose Aethina tumida and Tropilaelaps spp. will be described. Participants can share their methods. Are they specific? Is it possible to find a practical and valid method to be used by beekeepers without a laboratory? Conclusions: How do beekeepers diagnose honey bee diseases on field worldwide?

Looking forward to have a lively online discussion!

Giovanni Formato


Due to an unforeseen circumstance, the moderator of this discussion was not able to launch the discussion today as planned.  It will start tomorrow 8 July with a quick overview of the results of the survey conducted in 2015-2016 in collaboration with TECA on “Veterinary medicines in beekeeping around the word”. 

Apologies for any inconveniences.


Dear TECA followers,

My name is Giovanni Formato. I am a veterinarian working in the Honey Bee Health Laboratory in Rome, at the Istituto Zooprofilattico Sperimentale (IZS) (Regional Institute for Animal Diseases) of Latium and Tuscany (Italy). My area of work is mainly linked to the beekeeping sector, with a particular focus on the honey bee diseases diagnosis and control. For the next 5 weeks, I will be moderating this discussion on Simplified Field Methods for diagnosing honey bee diseases and Good Beekeeping Practices (GBPs) in beekeeping.

Feel free to ask any questions or to post comments.

What are the Good Beekeeping Practices (GBPs)? These are activities/practices that allow a proper management of the apiary to prevent bee diseases and at the same time, allow obtaining high-quality products respecting both the consumer’s health and the beekeeper’s health.

For example, GBPs that normally should be adopted in the apiary involve the following practices:

  •  Inspect the surroundings to place the apiaries in appropriate areas: non-humid, not exposed to cold winds, not subject to pollution sources such as intensive agriculture and industrialization (Fig.1); selection of suppliers of bees and beekeeping equipment, verification of the health status of swarms, colonies and queen bees;

Fig.1: Apiaries located in proper area

  • Observation of quarantine measures for all new introductions that have to be made in the apiary;
  • Identification of each hive by applying a unique numerical code for purposes of hive individuation and subsequent documentation (Fig.2);

Fig.2: Hives identification with numerical and graphical signs

  • Regular verification of the colonies health status during the year, through inspection of the bees and the new combs. The frequency of these checks depend on the season: reduction of inspections during winter period and under unfavorable weather conditions (Fig.3); 

Fig.3: Hives inspection under favourable conditions

  • Controls on the productivity and resistance to illness;
  • Frequent renewal of honeycombs (every 2 years) and regular replacement of queens (every 1-2 years), selection of queens who show resistance to diseases, hygienic behavior, docility, low tendency to swarm and high productivity;
  • Maintenance of colonies at similar strength, ensuring that hive capacity is sufficient to discourage swarming; preventing acts of looting (not having in apiary highly diseased, weakened colonies that are easily targeted to be sacked; perform maintenance of hives);
  • Adoption of appropriate techniques to ensure the welfare of colonies, especially those younger/weaker (feeding colonies having no food stocks or in case of unfavorable weather conditions as in autumn, winter and excessively cold or rainy spring; ensuring good wintering; providing adequate water supplies particularly in hot periods, etc.);
  • Provision of candy or glucose/fructose syrup avoiding the use of honey to feed the bees. Verification of origin and wholesomeness of supplies provided to the bees;
  • Appropriate use of the bee smoker (respecting the bees welfare and avoiding using toxic material that can contaminate the honey);
  • Elimination of use of toxic substances or paints for hives (e.g. Disinfectants, chemical treatments for wood, etc.);
  • Elimination of transfer of honeycombs from one colony to another if the colonies health status is unknown. Separation of sick from the healthy hives; destroying, if necessary, infected colonies;
  • Exclusive application of registered drugs for use in bees respecting instructions and guidelines, and recording drug use in the logbook. Improper and untimely use of chemicals during honey production may lead to its contamination;
  • Periodic mowing of grass in front of the hives;
  • Maintenance of the apiary and the beekeeping equipment in good conditions and always clean; ensuring the required maintenance and, when necessary, renewing the materials;
  • Referral to expert assistance in case of anomalies, whenever necessary.


Of course, one of the main GBP is to be able to recognize a honey bee disease in our apiary. The first step to honey bee disease field diagnose is: to know and to be aware of the different honey bee diseases.

Are beekeepers able to do that?

In order to gather information on the awareness of honeybee diseases, their management, and the assistance beekeepers receive to address honeybee issues, we have launched an online survey through TECA. This survey on "Veterinary medicines in beekeeping around the world: Which active ingredients are in use and do they respond to the needs of beekeepers?"  has been collecting information from beekeepers, inspectors, trainers, technicians, veterinarians, researchers and other beekeeping followers in 2015-2016. The survey and the information gathering was facilitated by the TECA Beekeeping Exchange Group.

According to the results of this Survey, beekeepers have generally a good knowledge on the honey bee disease (see Fig. 4 and Table 1).

Fig. 4 – Beekeepers knowledge on different honey bee diseases


Table 1 - Beekeepers knowledge on different honey bee diseases


Do this means that knowing the diseases, beekeepers are able to recognize them in the field?

To be real, this is not 100% true. But of course, this is a good starting point!



  1. In your Country, it is easy to receive general and Good Beekeeping Practices training on honey bee diseases?
  2. What methods do you consider of primary importance to detect honey bee diseases in the field? 


Dear Giovanni, I'm Jorge, a spanish veterinarian and beekeeper. I was wondering about the fact that GBPs could interest beekeeper's health aspect. Please, could you give more details on this aspect? Thanks Jorge

Dear Jorge, yes, GBPs include beekeeper's health aspect too.


This document is intended to help Competent Authorities to assist stakeholders, including farmers, to fully assume  their responsibilities at the animal production stage of the food chain to produce safe food and should also address socioeconomic, animal health and environmental issues in a coherent manner.

Therefore, farmer's (=beekeeper's) health aspect are included too.

In the document, the Good Farming Practices (GFPs) are divided into six groups:

   1. General farm management

   2. Animal health management

   3. Veterinary medicines and biologicals

   4. Animal feeding and watering

   5. Environment and infrastructure

   6. Animal and product handling

Why don't we try to list GBPs following this scheme?



Attached files: 

Dear TECA members,

Varroosis and viruses are the major honeybee diseases responsible for colony losses worldwide. The quantification of the number of mites inside the colony is fundamental, as well as the quantification of the viruses.

With this discussion, we can try to give a look at the available procedures/instruments/kits for beekeepers to diagnose on field the presence of varroa mites and viruses without a laboratory analysis.

Let’s start with VARROA DESTRUCTOR:

The first way to know if we have an infested colony is to see the signs of the varroa infestation on bees or brood. (see also: http://teca.fao.org/read/8416). Signs on adult bees are: bees with deformed wings and/or smaller abdomen, mites behind the head or nestled between the bee’s abdominal segments or walking on the combs (especially on brood combs).Bee with wings deformed (left), smaller abdomen (central) and with adults of varroa on their body (right).


Signs on brood are: 

blackened of bad smelling brood combs with  scattered sealed brood cells, containing bees dead in the cells at the end of metamorphosis with heads lifted up towards the cell opening with everted tongues.

Bees dead at the end of metamorphosis, smaller than usual, black, unable to exit from the cells (so called “mini-drones”).

If we extract larvae from the cells, we can observe the mite on the body of the bees.

In these cases, we immediately know that the parasite is present. But we need to quantify it, in order to establish if we have a serious infestation or not, if an acaricide treatment of the colony is urgently needed or not. In the table below, I listed some possible ways to detect and count the mites into the colonies with the respective PROS and CONS.

  Pros Cons

1. Count of mites on bottom boards killed by an effective (acaricide efficacy >90% (1)) acaricide treatment

Fast, if you want to have just an idea  of the infestation levels (wihout the need of to wait 21-24 days for the complete cycle of the bees): in few days you can have an idea of the amount of varroa on the adult bees.


Non destructive

Possible contamination of bee products in case of high environmental impact products application;


Time consuming, in case you want to have a more accurate idea of the total varroa present on both: adult bees and brood. In this case you should wait 21-24 days (for the complete cycle of the bees) and results are not immediate.

2. Count of mites inside the drone or worker brood Fast

Applicable only in some periods: i.e. when drone and/or worker brood is available



3. Count of natural mite fall with sticky sheets or grease on the bottom boards

Applicable by all beekeepers


Non destructive


Easy to apply, also during winter time

Time consuming to apply the sticky sheet/grease and to count the mites (usually 2 weeks of counts).

4. Count of phoretic mites (mites attached to the body of the bee) dislodged by using the icing sugar or other powders methods (e.g. flours) (2)



No residues

Environment friendly

Bee friendly (do not kill the bees)

Applicable by all beekeepers

Accuracy not so high


To be validated

5. Count of phoretic mites dislodged with the use of liquids (e.g. soapy water, ethanol)



No residues for hive products 

Destructive (kills the bees)

Accuracy not so high

To be validated 

6. Count of phoretic mites dislodged with the use of CO2



No residues

Environment friendly

Bee friendly (do not kill the bees)

Applicable by all beekeepers

Accuracy not so high

To be validated

[1] Usually 90% is the efficacy of an Oxalic acid treatment in absence of brood.  Higher efficacies (>95%)  are obtained by stronger environmental impact active principles (e.g. coumaphos, fluvalinate, amitraz, permethrin).

[2] See also technology developed by our colleagues in Chile: http://teca.fao.org/read/8663

If we consider only the instruments that can be used on field and can give an immediate idea of the varroa infestation of the colonies (so data that can be used to know if we have a high infestation and we have to carry out a treatment), we should compare only these methods:

  • Count of mites inside the drone or worker brood
  • Count of natural mite fall with sticky sheets or grease on the bottom boards;
  • Count of phoretic mites dislodged with the use of powders (e.g. icing sugar);
  • Count of phoretic mites dislodged with the use of liquids (e.g. soapy water, ethanol);
  • ​Count of phoretic mites dislodged with the use of CO2

Below you can find some pictures of available tools to carry out these evaluations:

Count of mites inside the drone or worker brood (% of varroa mites in the cells: number of mites/cells*100)

Count of natural mite fall with sticky sheets or greasy in the bottom boards

Count of phoretic mites dislodged with the use of powders (e.g. icing sugar)

(See also technology developed by our colleagues in Chile: http://teca.fao.org/read/8663)


Count of phoretic mites dislodged with the use of liquids (e.g. soapy water, ethanol).

Count of phoretic mites dislodged with the use of CO2



Do you use some of these methods or others? Do you think that these methods could be useful?

Now let’s talk now about VIRUSES.

The first way to detect a virus infection inside the hive is to detect the symptoms.

Viruses, even if present, are usually at low levels and asymptomatic, meaning there are no clear symptoms of viruses visible on the bees that the beekeeper can spot to diagnose in the field. 

But when one or more stressors intervene on the bees (e.g. absence of the queen, high varroa or nosema levels, absence of food, etc.) viruses are able to multiply and become symptomatic (symptoms are visible).

When viruses appear, the beekeeper should:

  1. before all, if possible, remove the stressors (e.g. varroa, nosema, pesticides, etc.) that caused the viruses increase.
  2. then, the beekeeper will take care of the colony by: administering external healthy adult bees, substitute the queen and/or administering extra-feeds (especially added with some integrators like minerals, vitamins or aminoacids).

When viruses appear, it is not said that the beekeeper will effectively be able to control them (above all in case of high viral levels or in case of too weak colonies).  For this reasons, the best way the beekeeper can control viruses is to prevent them, keeping under control the stressor that caused the viruses. These viruses are contagious and can contaminate other hives. For this reason it is important to avoid to move frames from affected hives to healthy hives.

A trained beekeeper can detect the signs of viruses on bees or brood.  The beekeeper should monitor the number of bees with symptoms in the hive. The soon (s)he starts to control the stressors the better will be the final results.

The diagnostic symptoms for the major virus of the honey bees have been described in detail by Bailey and Ball (1991) and can be summarized as follows (http://www.coloss.org/beebook/II/virus/1/1): 

Acute bee paralysis virus /Kashmir bee virus /Israeli acute paralysis virus

Acute Bee Paralysis Virus (ABPV), Kashmir Bee Virus (KBV) and Israeli Acute Paralysis Virus (IAPV) are three closely related viruses) that are largely symptomless, but they can be lethal at individual and colony level, particularly when transmitted by the varroa mite which is an active vector of these viruses. These viruses are characterized by the ability to kill both pupae and adult bees very rapidly (3-5 days) after strong inoculation of virus load by the saliva of adult females of varroa during their parasitation of the bees.

Pupae infected by the viruses fail to complete development and die in the cells, unable to exit.

Black queen cell virus

The main symptoms for Black Queen Cell Virus (BQCV) consist of blackened cell walls of sealed queen cells, containing dead pro-pupae. Diseased queen larvae have a pale yellow appearance and tough sac-like skin, much like sacbrood. The virus is present in adult bees too, without obvious symptoms.

During hive inspection, beekeeper should check if capped queen cells are dark in colour. If yes, open the cell and check if the queen pupae inside is black. In this case, try to take a frame with eggs (1 to 3 days) from another healthy colony and try to breed one or more new queen cells from that frame.

Deformed Wing Virus/Kakugo Virus

The symptoms for Deformed Wing Virus (DWV) consist of bees with crumpled and/or vestigial wings and bloated abdomen. Infected bees die soon after emergence. Asymptomatic bees can also contain heavily load of virus. The virus is detected in all other life stages as well, but without obvious signs. ‘Kakugo’ virus (KV) and other strains of DWV have been associated with elevated aggression in bees.

Deformed Wing Virus has been related to high varroa mite infestation.

Summary: During hive inspection, beekeeper should first check if (s)he finds around the hive bees with deformed wings (whenever possible: it is difficult if the colonies are located in fields or forest).

If a colony is particularly aggressive for no reasons (bees with high varroa levels can be aggressive), a beekeeper can check if (s)he sees bees with deformed wings and swollen abdomen. In this case (s)he should as soon as possible apply a varroa treatment.

Sacbrood Virus /Thai Sacbrood Virus

The clearest symptoms of Sacbrood Virus (SBV) appear a few days after capping, and consist of non-pupated pale yellow larvae, stretched on their backs with heads lifted up towards the cell opening, trapped in the unshed, saclike larval skin containing a clear, yellow-brown liquid.

The virus is also present in adult bees, but without signs. Diseased larvae are most commonly seen in spring, but the disease normally clears quickly with rapid expansion of the colony. Probably due to a imbalance among adult bees (fewer) and brood to be assisted (nutrition stress).

Summary:   when checking the brood combs, if the beekeeper find the sacbrood brood, he should administer an integrative nutrition to the bees.

Chronic Bee Paralysis Virus /Satellite Virus

Chronic bee paralysis virus (CBPV) manifests itself, especially during spring season, in adult bees through two distinct set of symptoms. One set consists of bees with trembling wings and bodies and unable to fly, causing them to crawl in front of the hive in large masses. They often have partly spread, dislocated wings and bloated bodies as well. The other set of symptoms consists of hairless, greasy black bees. These bees are attacked at the entrance by guardian bees and inside the hive by other healthy bees that keep them away from the brood. They soon also become flightless, uncoordinated, tremble and die. Frequently, large number of these bees can be observed in front of the hives (please, remind that if the hives are standing on grass, it is very difficult to see dead bees on the ground).


The virus also infects the larval and pupal stages, can be detected in faecal material and is efficiently transmitted through contact and feeding (e.g. trophallaxis).

CBPV is sometimes associated with a small “satellite” virus: Chronic Paralysis Satellite Virus (CBPSV; originally called chronic bee paralysis virus associate CBPVA that is of unknown significance to symptomatology.

Summary: during hive inspections, the beekeeper should first look around the hives if (s)he finds lots of dead hairless bees in front of the hive or bees crawling/trembling with wings partly open at the entrance or in the hive.

In this case, the beekeeper should take care of the colony by substituting the queen and/or administering extra-feeds (especially enriched with some integrators like minerals, vitamins or aminoacids).

Questions to the followers of this discussion:

To our knowledge, so far, there are no other field instruments/kits available for beekeepers to diagnose the presence of viruses in their hives. Advanced laboratory analyses (adopting biomolecular methods – like PCR) could be able to analyse affected bees (brood or adults) to confirm the diagnosis.

  • Do viruses affected your hives in your apiary? Is it the same now than in the past?
  • Do you have some other signs to suggest?
  • Do you know of some new kits available in your country to help you diagnose the mentioned viruses?
  • What other methods to diagnose do you use?

We are looking forward to reading about your experiences. Also, feel free to ask any questions you might have.


Dear Giovanni,

Thank you for this discussion. I am a starting beekeeper and the information you are sharing is very useful for me.

I have two questions:

1. how can I know if a varroa infestation is serious or not, and when is it necessary to apply a treatment of the colony. What is the best treatment?

2. you mention that when a beekeeper diagnoses sackbrood, he need to apply integrative nutrition to the bees. Can you tell me more about this?  Is it possible to make this integrative nutrition myself?

Thank you, Slavko

Dear Slavko,

I.                   Concerning VARROA, you can easily understand you are facing a serius infestation level of varroa observing the adult honey bees: you’ll see varroa on their bodies and/or bees with deformed wings.

In these cases, the best thing to do is to immediately apply a treatment.

What is the best treatment?

This depends mainly by two factors:

1)                 the external temperature. For example, you’ll never use in Winter or in Autumn evaporating essential oils, like thymol, that needs high temperatures to evaporate;

2)                 the presence or absence of brood in the colony. For example, there are some organic acids that are unable to kill varroa within the capped cells of brood (like oxalic acid or lactic acid), while other organic acids are able to kill varroa inside the brood cells (like formic acid).

If you consider the above mentioned points, together with the active ingredients’ leaflets of the products you can find on trade in your Country, you’ll get the proper treatment to apply in your area.


II.                Concerning the integrative nutrition for the bees, there are commercial feeds on-trade, but you can prepare by yourself a protein feed for bees administrating, inside the hive, 200-500g with:

- 85% of sugar: glucose, sucrose, fructose or honey (taken only from healthy colonies!);

- 10% of protein like sunflower, sorghum, soy flour or pollen (taken only from healthy colonies);

- 5 % fat

Adding yeasts (contain 50% of protein, 7% fat and B vitamins) and milk powder it is possible to increase the quality of the nutrition and the feed desirability for the bees.

Here some examples of recipes:

200 g of yeasts

100 g of pollen

400 g of powder sugar

100 g of milk powder

add honey or sugar syrup (70%sugar : 30% water) while mixing, in order to obtain a homogeneus solid candy.


50 g of yeasts

100 g of pollen

350 g of powder sugar

350 g of milk powder

add honey or sugar syrup (70%sugar : 30% water) while mixing, in order to obtain a homogeneus solid candy.


Best regards.


Dear Slavko,

to give you some supplementary material concerning the monitoring and the control of Varroa mites in colonies of honey bees, I send you the link where you can find a document of Jeff Harris from the US.


I hope you'll find it interesting....

Best regards.



Dear Giovanni,thanks a lot for your contributions.I have a question about the honey bee viruses:Is it possible an horizontal and vertical transmission of the viruses inside a colony?How could it happen? Thanks Best Marco

Dear Marco,

The horizontal transmission of honey bee viruses, usually happen in "stressed" colonies and create serious problems for bee health. This could happen with:

  1. a direct food-borne transmission, that can take place by eating pathogen-contaminated food and passing out viruses from the gut with feces (e.g. ABPV from nectar, pollen, honey and royal jelly; BQCV and DWV from pollen and honey; SBV from nectar; CBPV, KBV from pollen). In this case we find high viral quantity at the gut (and feces) level; 

  2. a venereal transmission, when viruses are transmitted between two sexes during mating  

  3. with the indirect transmission, by the parasitic mite Varroa destructor (e.g. DWV, ABPV complex).

Chen (Chen et al., 2006) demonstrated that six viruses including ABPV, BQCV, CBPV, DWV, KBV, and SBV were found in pollen samples and two viruses including BQCV and DWV were detected in the honey. If we consider that several behaviors of honey bees such as feeding brood, attending the queen, packing pollen, and processing nectar favor the probability of food-borne transmission, it is very important to apply the Good Beekeeping Practices to avoid this problem (e.g. do not feed the colonies with honey).The role of Varroa mites as a vector in acquiring and transmitting viruses from severely infected individuals to healthy bees in bee colonies has been experimentally demonstrated in several studies. The venereal transmission and the indirect transmission carried out by the Varroa mites could be reduced by applying acaricide treatments. For instance, to avoid the trasmission of viruses by drones, it is fundamental to have not-infested colonies (Varroa preferrably invades the drone cells). 


Honey bee viruses could be vertically (from the honey bee queen to the progeny) transmitted in the colony from queens to eggs.

When a colony is in healthy status, this is the usual trasmission, normally asymptomatic.A study by Chen (Chen et al., 2005) revealed that DWV could be detected in all developmental stages of honey bees, including adults, pupae, larvae, and eggs. Another study by Chen (Chen et al., 2006) examined the virus status of both mother queens and their offspring, including eggs, larvae, and adults simultaneously to further prove the existence of vertical transmission pathway. When queens were found to be positive for certain viruses, the same viruses were detected in their eggs, larvae, and adult worker bees, though neither queens nor their offspring exhibited any overt symptoms of disease. These data suggest that transmission of viruses from queens to their progeny is highly likely. 




  Chen,  Y.P.,  Pettis,  J.S.,  Feldlaufer,  M.F.,  (2005).  Detection  of multiple viruses  in  queens  of  the  honey  bee,  Apis  mellifera L..  J. Invertebr. Pathol. 90, 118–121

  Chen, Y., Evans, J., & Feldlaufer, M. (2006). Horizontal and vertical transmission of viruses in the honey bee, Apis mellifera. Journal of invertebrate pathology, 92(3), 152-159.)