Common Pests, Diseases and Disorders of the Adult Honey Bee€¦ · Symptoms seen in a colony vary according to the type of organism causing the disease. Many of these symptoms are

Common Pests, Diseases and Disordersof the Adult Honey Bee

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The Food and Environment Research AgencySand HuttonYorkYO41 1LZUKTelephone +44 (0)1904 462 000Fax +44 (0)1904 462 111Email [email protected] www.defra.gov.uk/fera

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Published by The Food and Environment Research Agency. Printed in the UK, November 2013,on material containing 80% post-consumer waste and 20% Elemental Chlorine Free pulp.

PollinationPollinating insects provide almost incalculable economic and ecological benefits to people,flowering plants and wildlife. Pollination by honey bees, which are the main managed pollinatorspecies throughout the world, and other insects are key steps in the production of manyimportant food crops that together comprise approximately one third of our diet. More thanthree quarters of crops cultivated in Europe and, worldwide, 70% of the 124 main crops useddirectly for human consumption, are dependent on pollinators. The UK’s crop pollinationindustry has an estimated value greater than £400 million every year. Pollinating insects arealso vitally important for the pollination of wild flora. With this in mind, it is easy to see whyhoney bee health is so important and why beekeepers should remain vigilant to pests anddiseases that damage these essential pollination providers.

Pollination

Honey bee on willow

Common Pests, Diseases andDisorders of the Adult Honey BeeHoney bee colonies are subject to a number of pests, infections, diseases and disorders thataffect adult bees. This leaflet describes the recognition and management of some of the morecommon of these: Tracheal mites (Acarapisosis), Nosemosis, Dysentery and certain viruses.Symptoms seen in a colony vary according to the type of organism causing the disease. Many ofthese symptoms are non-specific and their severity largely depends upon the vigour of theaffected colony. The common pests and diseases of adult bees are generally less serious thanthe brood conditions of American foulbrood (AFB) or European foulbrood (EFB). However, it isstill very important that beekeepers are aware of the causes and symptoms of adult beedisorders and the best practices that will help to minimise their effects.

AcronymsAFB American foulbroodBBKA British Beekeepers’ AssociationBDI Bee Disease InsuranceBFA Bee Farmers’ AssociationBQCV Black queen cell virusCBPV Chronic bee paralysis virusCCD Colony Collapse DisorderDARDNI Department of Agriculture and Rural Development Northern IrelandDefra Department for Environment, Food and Rural AffairsDWV Deformed wing virusEBV Egypt bee virusEFB European foulbroodFera Food and Environment Research AgencyGLP Good Laboratory PracticeISO International Standards OrganisationIPI Insect Pollinators InitiativeIPM Integrated Pest ManagementNBI National Bee InspectorNBU National Bee UnitOIE Office International des EpizootiesRAS Random Apiary SurveyRBI Regional Bee InspectorSASA Science and Advice for Scottish AgricultureSBI Seasonal Bee InspectorVMD Veterinary Medicines DirectorateWBKA Welsh Beekeepers’ AssociationWG Welsh Government

About this leaflet

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Help and advice 3The National Bee Unit 3BeeBase 3Why is it so important to register on BeeBase 3How to sign up to BeeBase 4How do I know that my details are secure 4Beekeeping Associations 4

Pests Diseases and Disorders of adult bees 5Tracheal mites (Acarapisosis) 6

Description of tracheal mite disease (Acarapisosis) 6Methods of transmission of tracheal mites 7Symptoms of Acarapisosis 7Effects of Acarapisosis on infested colonies 8Diagnosis of tracheal mites 8Treatment and control of tracheal mites 10

Nosema 10Description of Nosema disease (Nosemosis) 10Methods of transmission of Nosema 10Effects of Nosema on the colony 12Diagnosis of Nosema infection 12Treatment and control of Nosema 13

Dysentery 13Description of Dysentery 13Dysentery as a symptom of poor diet 13Dysentery and Amoebic disease 13Methods of transmission of Amoeba 14Treatment and control of Dysentery 14

Viruses 15The significance of honey bee viral diseases 15Control of honey bee viruses - a general message 15Symptoms and diagnosis of deformed wing virus (DWV) 15Methods of transmission of DWV 16Chronic bee paralysis virus (CBPV) 16Methods of transmission of CBPV 17Treatment and control of CBPV 17

Diagnostic Services at the NBU 17Useful addresses 18References and acknowledgements 19Notes 20

Contents

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Help and advice

The National Bee Unit

The Food and Environment Research Agency’s(Fera’s) National Bee Unit (NBU) provides anintegrated statutory and advisory service tobeekeepers in England and Wales. It providesdiagnostic, consultancy and research services to Defra, Welsh Government, the ScottishGovernment, commerce and beekeepers. The NBU is a recognised centre of excellence in theprovision of advice and research in bee health. The Unit’s laboratories are fully compliant with the international Good Laboratory Practice (GLP) and ISO 9001 quality schemes to ensure a highprofessional standard, and use as a base, theOffice International des Epizooties (OIE) Manuals ofStandard diagnostic tests for laboratory diagnosis.Most staff are trained practical beekeepers as wellas scientists and are supported by teams ofspecialists across the rest of Fera(www.defra.gov.uk/fera).

The Unit has modern facilities, includinglaboratories with computer support throughBeeBase (see next section), as well as 150 colonies and the apiary buildings to support them.

The NBU has a bee health inspection and advisoryservice operating in England and Wales, comprisinga regional network of Inspectors. The head of fieldinspection services is the National Bee Inspector(NBI). Regional Bee Inspectors (RBIs) reporting tothe NBI manage teams of Seasonal Bee Inspectors(SBIs) throughout England and Wales. As well asthe statutory inspections and apiary surveillanceprogramme, Bee Inspectors provide free adviceand assistance to beekeepers on a range of beehealth issues and run training courses forbeekeepers on disease recognition, disease controland good husbandry, often in conjunction with localBeekeeping Associations. The NBU team deliversaround 500 training events every year. BeeInspectors also assist with field trials within theNBU’s Research and Development programmes.

For further information contact the NBU, who willput you in touch with the appropriate Bee Inspectorfor your area, or visit the NBU’s BeeBase websitekey contacts pages (https://secure.fera.defra.gov.uk/beebase/public/Contacts/contacts.cfm).

The NBU has broad research and developmentinterests (current list outlined on BeeBasehttps://secure.fera.defra .gov.uk/beebase/index.cfm?sectionid=48). Our portfolio coversvarroacide development, EU-wide colony losssurveillance, risk assessment and novel controlmethods for exotic pest threats and the economicsand biology of pollination. The NBU is a contributorwithin the Insect Pollinators Initiative (IPI)(www.bbsrc.ac.uk/pollinators), leading researchinto systems that model the epidemiology ofdisease to enable improved management in thefuture. We are also using advanced moleculartechniques to identify specific bacterial straintypes, which will add to our understanding of thespread of serious brood diseases. The NBU worksin partnership with many Universities andOrganisations both in the UK and overseas toachieve these shared research goals.

BeeBase is the NBU’s award winning website.BeeBase contains all the apicultural informationrelating to the statutory bee health programme inEngland and Wales. In June 2010, the informationfor the Scottish inspections programme was alsoincorporated into BeeBase. BeeBase contains awide range of beekeeping information, such as theactivities of the NBU, the bee related legislation,pests and diseases information including theirrecognition and control, interactive maps, currentresearch areas, publications, advisory leaflets andkey contacts. To access this information visit theNBU website (www.nationalbeeunit.com). Manybeekeepers find this website to be a very usefulsource of information and advice. In addition to thepublic pages of the BeeBase website, registeredusers (see below) can view their own apiaryrecords, diagnostic histories and details.

Why is it so important to register onBeeBase?

As well as containing useful information onbeekeeping, BeeBase is a vital tool in the control of bee disease and pests. Where statutory pests or diseases (for example, foulbrood) are confirmed,the NBU can use BeeBase to identify apiaries at

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risk in the local area and, as a result, targetcontrol measures effectively. By knowing wherebees are, we can help you manage disease risks inyour apiaries. Such risks include the incursion ofserious exotic pest threats (for example Small hivebeetle). The more beekeepers who are registered,the more rigorous our bee health surveillance canbe and, crucially, the better our chances ofeliminating pests and diseases.

How to sign up to BeeBase

If you are not yet registered please visit the publicpages of BeeBase where you can sign up onlineat: www.nationalbeeunit.com. Otherwise you canget in touch with the NBU office team who will behappy to help. You can email us at:[email protected] or contact us by telephoneon: 01904 462510. By telling us who you are, youwill be playing a very important part in helping tomaintain and sustain honey bees for the future.

How do I know that my details will be secure?

All of the information that you provide for thepurposes of registration on BeeBase is covered bythe Public Service Guarantee on Data Handling(see Confidentiality page of BeeBase). In addition,all data will be handled according to rules statedin the Data Protection Act, 1998. All levels ofaccess to BeeBase are protected in the same wayas on-line banking. Your personal access ispassword protected. When you first register youare allocated a temporary password, which is validfor your first visit only. You will then be promptedto set your own password. You need to ensure thatyour own password remains confidential. You willalso be able allocated a personal ID Number,which relates solely to you. As a personallyregistered beekeeper, once you have received aninspection visit, you can check your own record onBeeBase. If you wish, you can make use of theapiary records system if you want to record yourapiary visits. Your SBI, RBI, NBI and NBU staff atFera will have access to your records, but noInspector or NBU staff member will ever discloseto others that you have been inspected or anydetails about your bees or beekeeping withoutyour consent. Although BeeBase includes publicpages containing information such as disease,

colony losses, leaflets, useful links and muchmore general information, the public has noaccess to your or other beekeepers’ details.

Beekeeping Associations

In many areas, Beekeeping Associations operatedisease control training schemes and providepractical advice and advisory leaflets to memberson bee disease recognition and management.Contact your local Beekeeping Association or beehealth advisor for details (England -www.bbka.org.uk; Wales - www.wbka.com).

Help and advice

Figure 1. Fera laboratory, Sand Hutton, York

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Adult honey bees are susceptible to a variety of pests, disorders and infections. This leaflet describes a selection of the mostcommon ones: Tracheal mites (Acarapisosis), Nosemosis, Dysentery and certain viruses (Varroa and exotic pest species arecovered in separate leaflets that can be downloaded from the NBU’s BeeBase website www.nationalbeeunit.com). Symptomsseen in a colony vary according to the type of organism causing the disease. Many of these symptoms are non-specific and sothe only way of confirming the presence of a pathogen is through appropriate laboratory diagnostics. Their severity largelydepends upon the vigour of the affected colony. The common diseases of adult bees are generally less serious than the broodconditions of American foulbrood (AFB) or European foulbrood (EFB). However, it is still very important that beekeepers areaware of the causes and symptoms of adult bee diseases and the best practices that will help to minimise their effects.

It is also important to note that the pests and diseases described in this leaflet are often only apparent when colonies are inpoor condition — their effects being suppressed in large, thriving colonies. Good beekeeping is therefore the best way toensure that honey bee colonies remain healthy. In many cases, spread of disease can be reduced by good husbandrypractices. Thriving colonies need to be:

• strong and vigorous with plenty of brood

• routinely monitored and treated for Varroa infestations

• well fed (honey and pollen)

• headed by fertile queens, preferably not more than two years old, and of good stock

• free from foulbrood diseases - brood must be examined at least every spring and autumn for signs of AFB and EFB (see the NBU’s Foulbrood leaflet)

• colonies must have adequate comb space to allow expansion and food storage

• the swarming impulse must be controlled

Pests, diseases and disorders of adult bees

Pests, diseases and disordersof adult bees

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Tracheal mites (Acarapisosis)

Tracheal mite infection (known as Acarapisosis orAcarine) is an infestation of the respiratory systemof adult bees by the parasitic tracheal miteAcarapis woodi. This system consists of a complexarrangement of breathing tubes (trachea) and airsacs. These carry air to all organs of the body, fromten pairs of openings (spiracles) situated alongeach side of the thorax and abdomen. Trachealmites can infest all castes - queen, workers andespecially drones. Mites usually infest adult beeswhen they are less than 3 days old, but older (up to 10 days) bees are also susceptible, particularlywithin the winter cluster. The mite reproducesinside the trachea leading into the thorax from the first pair of spiracles. A honey bee becomesinfested when a female mite (Figure 2) crawlsthrough the spiracles and enters these tubes,attracted by the vibration of the wing roots, and bypuffs of air coming out during respiration. Shequickly lays eggs inside the tracheae, usually no

later than one or two days after initial infestation(Figure 3). Female mites lay on average just oneegg per day. These hatch into young mites(nymphs), which moult several times beforereaching the adult stage a few days later. Bothnymphs and adults obtain their food by using theirpointed mouthparts (stylets) to pierce the wall ofthe trachea and suck on the host’s blood(haemolymph). Typically, a single female mite willproduce 20 offspring during her lifespan.Development time for female mites is about twoweeks and slightly shorter for males (11 to 12days). Usually only one generation of mites isproduced with a single host, but two generationsare possible in longer-lived autumn or winter bees.Multiple infestations, where a single bee hostsseveral adult mites, are common.

Description of tracheal mite disease (Acarapisosis)

Figure 2. Female tracheal mite seen under a high magnification Scanning Electron Microscope

Tracheal mites (Acarapisosis)

Methods of transmission of trachealmites

Mated adult female mites must leave their honeybee host before it dies, and infest a fresh adult bee.This is the only time that mites may be foundexternally on the bees. Tracheal mites cannotsurvive for more than a few hours outside theirhost, so this transfer has to take place as quicklyas possible, inside a colony. The female mite exitsthe trachea through the spiracle and uses her hindlegs to anchor herself to one of the bee’s bodyhairs. She then reaches out with her forelegs tograsp the hair of another passing bee. Only young bees in the first 10 days of adult life aresusceptible, due to the fact that the hairs in thetrachea are not fully hardened and thus allowmites to enter. The spread of the mite thereforedepends on the presence of young bees in the hiveand their close contact with older, infested bees.Approximately 85% of all bee-to-bee mite transferstake place at night, when the honey bees arerelatively inactive. Dispersal of tracheal mitesbetween colonies occurs by robbing, beekeeperstransferring bees from infested to un-infestedcolonies, swarming or, more often, through driftingof individual workers or drones.

Symptoms of Acarapisosis

Adult bees that are infested with tracheal miteswill cluster in front of the hive, appearing confusedand disorientated, unable to return to the colony.Large numbers of bees may also be seen crawlingup stems of grass in front of the hive (Figure 4).Such behaviours are not, however, clear indicationsof Acarapisosis: not only are they associated withother pests and diseases; even bees that areseverely infested with mites can behave in anormal way, in spite of the fact that their trachealwall has been damaged. Detection under a lowpower microscope after simple dissection of thebees is the only reliable method of diagnosis (seenext section).

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Figure 3. Eggs of the tracheal mite blocking the tracheaof a honey bee (high magnification Scanning ElectronMicroscope)

Figure 4. Crawling up a grass stems - a sign of diseasein adult honey bees

Effects of Acarapisosis on infestedcolonies

In some countries, tracheal mites have causedconsiderable damage and loss of colonies,particularly when mites first arrive in a country andbees are initially exposed to infestation. However,although honey yield may be reduced in colonieswith tracheal mites, in the UK Acarapisosis is notusually a serious disease, with low numbers ofcolonies being affected. Mite levels in individualcolonies vary and are lowest in the late spring andearly summer, generally increase in the latesummer and autumn, and are not easily detectedin winter. The springtime declines in miteprevalence are often associated with nectar flowsand rapid honey bee population growth. During thebees’ active season infestation has little effect onworkers’ performance, but lifespans of over-wintering bees are shortened, leading to ‘springdwindling’: the winter bees die early in the spring.If a colony goes into winter with an infestation levelof >30% then it is unlikely to survive.

Diagnosis of Tracheal mites

Acarapisosis can only be reliably diagnosed by carrying out dissection and microscopicexamination of honey bees’ primary trachea. The following tools are required for dissection and microscopic examination (Figure 5):

• a binocular dissecting microscope with a magnification up to x40, and a cool,concentrated light source

• a double dissecting needle

• a pair of fine-pointed steel forceps

• a small sheet of cork

To determine the level of infestation in a colony it is best to dissect and examine 30 freshly deadbees. Each recently-killed adult bee is laid on itsback and pinned firmly to the cork by pushing thedouble needle at an angle through the thoraxbetween the coxal joints of the second and thirdpairs of legs (Figure 6a). The head and forelegs ofthe bees are firmly gripped between the forceps’blades (Figure 6b) and together detached cleanlyfrom the body by a sharp pull of the forceps awayfrom the bee and slightly upwards (Figure 6c). Theaperture now left in the thorax is focused underthe microscope. The chitinous collar surroundingthe aperture must now be removed to expose thethoracic breathing tubes. The collar (Figure 6d and 7a) is gripped with the points of the forcepswhere it is narrowest, and peeled off with a rotarymotion of the closed forceps. The clean removal ofthe collar requires practice.

Figure 5. Diagnosis of tracheal mites by dissection and light microscopy

Figure 6a. Pinning out the bee for dissection

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Tracheal mites (Acarapisosis)

In a healthy, uninfested bee the trachea have auniform, creamy-white appearance (Figure 7a). In infested bees the trachea show patchydiscolouration or dark staining, (melanisation,caused by mites feeding (Figure 7b)), although earlyinfestation may be marked only by translucent areasthat indicate the position of individual mites or eggs.In extreme cases of very heavy infestation a bee’strachea may appear entirely blackened with darkbands. At higher magnifications (Figure 8), the eggs,nymphs and adult stages of the mite may also beseen in the trachea.

Figure 6b. Grip the head and forelegs with forceps as indicated by the dotted line (magnification x40)

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Figure 6c. Exposing thoracic collar after removal ofhead (magnification x40)

Figure 6d. The thoracic collar of the honey bee(magnification x40)

Figure 7a. Breathing tubes of a healthy bee – note their ‘r’-shape and uniform, creamy-white appearance(magnification x40)

Figure 7b. Breathing tubes of an infested bee – notepatchy discolouration (magnification x40)

Tracheal mites (Acarapisosis)

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Treatment and control of Trachealmites

At the time of writing (Autumn 2013) there is no proprietary treatment registered under theMedicines Act, available for Acarapisosis.However, this situation may change. The NBUregularly updates its BeeBase website with thelatest disease control advice for beekeepers. Seehttps://secure.fera.defra.gov.uk/beebase/index.cfm?pageid=192 or contact the NBU for advice. Thebest method of control available to the beekeeperis to re-queen colonies that are susceptible to thedisease. As with other adult bee diseases, it isimportant that colonies are kept large, thrivingand able to suppress infestation without chemicaltreatment.

Description of Nosemadisease (Nosemosis)Nosema disease, or Nosemosis, is caused byeither of the two species of Nosema identified inadult honey bees. These are N. apis and an Asianvariant, N. ceranae, which was first detected in theUK more recently (2008). Both Nosema species arehighly specialised ‘microsporidial’ parasites that

multiply within living cells of the gut and both are widely distributed in the UK. Adult workers, drones and queens are all susceptible. Nosemaspp. germinate to invade the digestive cells liningthe mid-gut (epithelium) of adult bees where theymultiply rapidly. The reproductive cycle of thepathogen progresses, eventually producing newmature spores (endospores), which germinate toinfect neighbouring host cells. Nosema spores areshed into the gut when the host cell ruptures,where they either infect more epithelial cells orare later excreted by the bees. Under optimalconditions Nosema completes its development in48 - 60 hours.

Methods of transmission of Nosema

Heavily infected bees generate many millions ofspores, which remain viable for at least a year oncontaminated hive material, thus acting as apotential source of further infection. Honey beesnormally defecate away from the hive, but duringlong periods of confinement they may soil thecombs. They are also more likely to defecatewithin the cluster during late winter and soNosema may spread most rapidly in the springwhen the brood nest is expanding, particularly ifnormal comb cleaning behaviour coincides withconfinement of foraging bees. Cell cleaning priorto storing autumn-fed sugar syrup (when littlenatural forage is available) may also result in thespread of Nosema infection. Infection is easilyspread by beekeepers placing combscontaminated with Nosema spores into healthycolonies - it is very important not to transfer soiledcombs between hives. A large survey conducted bythe NBU in 2009-2011 (called the Random ApiarySurvey (RAS)), demonstrated that 40% of apiariesin England and Wales were infected with N.ceranae, while 45% of apiaries were infected withN. apis. The results showed that many apiariesacross England and Wales contained both speciesof Nosema but interestingly, very few colonies fromthe apiaries sampled showed symptoms ofNosemosis. These results suggest that a colony in good condition is generally able to cope withNosema infection without it causing any noticeableproblems. As always, good husbandry and apiary

Figure 8. Adult tracheal mite together with eggs andnymphs, teased out from the trachea of an infestedhoney bee (high magnification Scanning ElectronMicroscope)

Nosema

Nosema

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management practices are vital in maintainingvigorous, healthy stocks, which are more able towithstand infection.

Infection with N. apis is often associated withsymptoms of dysentery (see later section) - darkbrown faecal matter splattered onto the hiveentrance or across the frames (Figures 9a - 9c).Dysentery is not directly caused by thesepathogens but by other factors such as fermentedsyrup. Dysentery then exacerbates the disease andhelps to spread Nosema throughout the colony.These effects can be worsened during periods of

prolonged confinement such as inclement weather,especially during the spring, when bees are forcedto defecate in the hive, further contaminating thecolony.

In Spain and other Mediterranean countries it has been reported that N. ceranae infections arecharacterised by a progressive reduction in thenumber of bees in a colony until the point ofcollapse. The beekeeper may also see a significantdecline in colony productivity. Eventually theaffected colonies contain insufficient bees to carryout basic colony tasks and they collapse. However,in northern European countries N. ceranae is notconsidered to be a significant pathogen. Unlikewith N. apis, dysentery and mortality in front ofhives are not commonly reported symptoms of N. ceranae infection.

Figures 9a and 9b. Signs of N. apis infection showingdark brown coloured faeces on the top bars and at hiveentrance

Figure 9c. Nosema infection - faeces on comb

a

b c

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Nosema

Effects of Nosema on the colony

The severity of Nosemosis is highly variable, butinfected colonies are certainly less productive.Nosema infection shortens the life span of bees.Infected bees have under-developed fat bodies -i.e. the food storage cells that line the abdominalwall and provide the nutrients from which nursebees produce brood-food and which also providenutrients for bees in the winter. The brood-foodglands of infected bees are also under-developed.Queens that contract the disease lay fewer eggs(because their ovaries degenerate more quicklythan uninfected ones) and are likely to besuperseded. A high level of infection thereforeresults in reduced brood rearing and a reductionin honey production. The effects of Nosema on a colony may be aggravated by the presence ofcertain viruses. Serious damage to coloniesinfected with Nosema is, however, uncommon.Only a small proportion of a colony normallybecomes infected in a large, well-maintainedcolony.

Diagnosis of Nosema infection

The clinical symptoms associated with Nosemainfection can be seen with other types of colonyconditions, so cannot be used to provide reliablediagnosis. A crude method to detect Nosema usesa light microscope to confirm presence of spores,as follows:

1. Using a pestle and mortar, crush the sample of bees (30 adults) in a little water.

2. Place a small drop of the resulting suspensiononto a microscope slide and cover with a glasscover slip; the amount of liquid used should bejust sufficient to fill the area under the coverslip.

3. Examine the suspension under the lightmicroscope, magnification x400.

4. The spores of both N. apis and N. ceranaeappear as translucent, greenish, rice shapedbodies (Figures 10a and 10b).

5. Spores of N. ceranae are more variable inshape and size than those of N. apis. They tend to be thinner, with a slight concaveappearance.

Since both species are virtually identical in sizeand shape when viewed using conventionalmicroscopy (Figure 10), the NBU uses moresensitive tests when it is necessary todiscriminate accurately between species. Severalother more sophisticated tests are available,which focus on the detection of species-specificgenetic material, the most advanced of thesemolecular methods being sufficiently sensitive todetect and measure extremely low levels ofinfection in colonies and in individual bees.

Figure 10a. Nosema ceranae and Figure 10b. Nosemaapis (x400 magnification)

a

b

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Treatment and control of Nosema

In large, thriving colonies, Nosema infection isusually suppressed and rarely reaches levels thatwarrant control treatments. (Note that if Nosemais controlled, then this also effectively controls itsassociated viruses). In the past, beekeepers wereable to treat Nosema-affected colonies with theantibiotic Fumidil B (active ingredient Fumagillin).However, this drug is no longer authorised in theUK for control of either Nosema species. In fact,research shows that it can have adverse effectswhen administered to a colony: treatment maysuccessfully suppress infection withoutnecessarily eradicating pathogens; at the sametime, beneficial micro-organisms are killed; socontrol of the pathogen is only temporary and asa result, residual infection can rapidly resurge toeven more damaging levels than seen pre-treatment.

For more information please visit the Nosemapage of BeeBase (www.nationalbeeunit.com). Forup-to-date advice on the availability of medicinesplease visit the Veterinary Medicines Directorate(VMD) website at: http://www.vmd.defra.gov.uk/ProductInformationDatabase

Given that Nosema is readily transmitted bysoiled, infected combs, husbandry methods suchas comb sterilisation and replacement are usefultools in managing disease and limiting spread.Make sure, therefore, that empty brood combstaken from colonies are sterilised before re-use.Sterilise combs by exposing them to the fumes of80% acetic acid. This is made adding one partwater to four parts glacial acetic acid. The acidshould be handled with great care; takeprecautions to avoid contact with the skin or eyes. Splashes on the skin should be washed offimmediately. Place the combs, with normalspacing, into hive boxes that are then stacked. In the bee spaces between each box in a stack,place a wad of cotton wool or other absorbentmaterial, pre-soaked in 100 ml of acetic acid.Obvious gaps in the stack must be sealed toprevent the fumes escaping. Leave the stacksundisturbed for one week in a well-ventilated

shed or a draught-free area outside. The fumeskill Nosema but do not harm honey or pollenstored in the combs. However, the acid fumes willcorrode any exposed metal surfaces. Metal endspacers need to be removed before fumigation,and should be scalded in hot water containingwashing soda. The combs must then be airedbefore use, making sure that any combscontaining honey are aired under cover, as aprecaution against robbing. For further details of this method see our ‘Hive Cleaning andSterilisation’ factsheet on BeeBase.

Description of Dysentery ‘Dysentery’ describes heavy soiling of hives orcombs by the faeces of adult bees (Figures 9a -9c). It is not caused by an infection, but by otherfactors such as poor nutrition. This condition isnot usually serious, but it can exacerbate theeffects of any disease that is present in a hive andhas been associated with the death of colonies.

Dysentery as a symptom of poor diet

Dysentery occurs when bees feed on ‘unsuitable’stores, such as honey or sugar with unusuallyhigh moisture contents – bees are unable toretain the large accumulation of water in theirbowels, resulting in diarrhoea. Fermented storesalso stimulate dysentery, as will acid-invertedsucrose. Although the latter is often believed tobe nutritionally suitable for bees because of itssimilarity to honey, in fact it contains toxins thataggravate water accumulation in the gut.

Dysentery and Amoebic disease

The previous section described the association of dysentery with N. apis, and it is likewise seen with/worsens cases of infection byMalpighamoeba mellificae - a single-celledparasite that affects the excretory organs(malpighian tubules) of adult bees. All castes aresusceptible, but drones and queens are rarelyinfected. Infection occurs when cysts (Figure 11),

Dysentery

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the dormant form of the parasite, are ingestedfrom the faeces of infected bees. Thesegerminate, invading the malpighian tubules,where they multiply at the expense of theexcretory cells of the bee. Cysts pass into therectum to be discharged with the faeces.

Methods of transmission of Amoeba

As the Amoebae replicate, they pack the lumen(tissue contained within large intestines, veins andarteries) of the tubules. There can be as many ashalf a million cysts/bee, which are shed in thefaeces. Amoebae are spread when soiledbeekeeping equipment is transferred into ahealthy colony.

Symptoms and diagnosis of Amoeba

There are no specific symptoms associated withAmoebic disease and precise effects of infectionon colonies are unknown. Infection with M.mellificae has not only been associated withdysentery, but also spring dwindling and shortenedlifespan of infected bees. The similar transmissionmechanisms for Nosema and M. mellificae (oral-faecal route) mean that they are often foundtogether (although neither is dependent on the

other), and it is likely that a dual infection will bemore damaging to the health of the honey bee.The incidence of M. mellificae is low in Englandand Wales. Diagnosis depends on examination ofadult bees under a microscope for the presence of Amoebic cysts, using the same method aspreviously described for Nosema (Figures 10a and 10b).

Treatment and control of Dysentery

Irrespective of its cause, there is no effectivetreatment for dysentery, and cleansing flights thatmay alleviate the problem are entirely dependenton the weather (more common on warm, dry,windless days). However, there are steps that canbe taken to reduce the risk of occurrence:

• As always, good husbandry and apiarymanagement practices are vital in maintainingvigorous, healthy stocks that are more able towithstand infection.

• Autumn feeding should be completed by thefirst week of October – allowing time for thecolony to take down the sugar syrup, reducingits water content to a safe level before theonset of cold weather. See our ‘Best practiceguidance notes Number 7 feeding bees –sugar’ on BeeBase.

• Avoid feeding bees with fermented honey orsugars of uncertain origin.

• Use only refined sucrose, table sugar or readymade syrup mixtures (such as Ambrosia,Apisuc or equivalent).

• There are currently no approved proprietaryproducts registered for the control of Amoebicdisease in the UK, but combs from infectedcolonies can be sterilised for re-use with aceticacid (see ‘Hive Cleaning and Sterilisation’factsheet on BeeBase).

Figure 11. Amoeba cysts (circled)

Dysentery

15

The significance of honeybee viral diseasesAdult honey bees are subject to infection by a rangeof different viruses, which vary in their incidence andthe severity of symptoms they can cause. All ofthem have at least the potential to cause harm, butoutbreaks of most viral diseases are infrequent in the UK. Sub-clinical viral infections are, however,very common. These impact on the overall health ofaffected colonies, shortening bees’ lives and makingthem more susceptible to other types of pests andpathogens that they might otherwise have been ableto resist. For example, the presence or absence ofviruses linked with Nosema or Varroa could accountfor the considerable variations reported in theapparent effects of these parasites. Few honey beeviruses elicit well-defined signs of disease and mostare therefore not easy to diagnose. In followingsections we provide information about just two ofthe more common viruses of adult honey bees,which can on occasion exhibit recognisablesymptoms.

Beekeepers will be aware that certain viruses havebeen associated with the condition ‘Colony CollapseDisorder’ (CCD). This phenomenon, characterisedby specific symptoms (sudden absence of themajority of the adult worker bee population,although the queen and plenty of stores remain) hasbeen reported in the USA but has never beenconfirmed in the UK. The viruses (and otherpathogens) that have been linked to its presence inAmerica are extremely rare in the UK. On thosevery rare occasions that they have been detected inbee samples, (collected for the purposes ofresearch carried out by the NBU), they have notbeen associated with symptoms of CCD. To date,CCD is believed to be absent in UK honey bee stocks.

Control of honey bee viruses – a general message

Chemotherapeutic treatments now availableagainst Varroa should, if correctly used andapplied at the correct time, indirectly suppress

those viruses associated with this parasite. Theywill not, however, help you manage viruses thatare introduced or spread independently of themites. As yet, there are no known direct methodsof controlling any honey bee viruses. The messagefor any viral disease, irrespective of the causativespecies, is the same - As a beekeeper, you canminimise the incidence and impact of viral diseasesin your colonies by doing the following:

• Keeping strong, healthy colonies.

• Monitoring regularly and treating for Varroainfestations.

• Treating colonies for disease when Varroapopulations are low (i.e. before the mites reachdamaging levels).

• Adhering to good apiary hygiene practices.

• Cleaning your equipment between each hiveexamination.

• Good beekeeping management.

For more information on these topics see ouradvisory leaflets at: https://secure.fera.defra.gov.uk/beebase/index.cfm?pageid=167 Alternatively, if you do not have the internet, thenyou can contact the NBU directly and requestrelevant material to be sent out to you (see detailsat the beginning of this leaflet).

Symptoms and diagnosis of deformedwing virus (DWV)

In the absence of Varroa, deformed wing virus(DWV) persists at low levels in infected colonieswithout causing any signs of infection. However, inthe presence of the mite, DWV causes clinicalsymptoms in developing pupae, including pupaldeath. Newly emerged bees from affected coloniesshow deformed or poorly developed wings. Theappearance/extent of deformity depends upon thestage at which individual bees become infected(Figure 12). Additional symptoms include abloated, shortened abdomen. The virus multipliesslowly, and pupae infected at the ‘white-eyed’stage of development survive to emergence but

Viruses

16

Methods of transmission of DWV

Transmission of DWV occurs via several routes,not all of which can be controlled by thebeekeeper. These include:

• Through the bees’ feeding activities; an infectednurse bee offering food to uninfected healthybrood, bees or the queen.

• Through bees’ mating activities between ahealthy virgin queen and an infected drone.

• An infected queen laying an infected egg.

• Varroa mite feeding activities can greatlyincrease levels of infection in a host, being avector to many viruses.

• Infection can occur at a colony level throughswarming and division.

Remember that viruses such as DWV aremanageable by the colony itself if the bees arestrong and placed under little stress. Alsoremember that a healthy host/pathogenrelationship is essential for both to survive. A viruscan often exist in a honey bee at such low levelsthat the individual bee’s fitness is not affected and so a balance between the two is created. It iswhen one factor gets out of control that othersymptoms, which may have been lying dormant,will start to flare up and become visible to thebeekeeper.

Figure 12. Symptoms of DWV

Figure 13a. Dead and dying honey bees in front of hive

Figure 13b. Honey bees showing signs of CBPV - a lackof hairs gives the bees a characteristic shiny appearance

Viruses

are malformed and soon die. Brood may dieearlier in development, and bees infected as adults appear normal until death. (Recentresearch into honey bee colony health in Englandand Wales has found that colonies with DWVinfecting adult bees or brood are likely to be halfthe size of virus free colonies). It is important tounderstand that although you may not see anysigns of DWV in your apiary, it does not mean thatit is not there. Factors such as a healthy beeimmune system and low Varroa populations couldbe keeping the virus suppressed until mitepopulations increase and the immune systemcannot cope, resulting in overt signs of infection.

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Chronic bee paralysis virus (CBPV)

Chronic bee paralysis virus (CBPV) has a widespreaddistribution in Britain but is rarely found infectinghoney bees. Colonies may carry CBPV withoutshowing symptoms. Symptoms, when present(Figures 13a and 13b), may include bees crawlingon the ground outside the hive entrance, vigoroustrembling of bees and hairless or bloatedabdomens caused by distension of the honey sacwith liquid. (See video footage of CBPV affectedbees at: https://secure.fera.defra.gov.uk/beebase/index.cfm?pageid=275). These visualsymptoms are reasonably reliable in diagnosingthe disease. Bristles on the bee’s body are easilydamaged in these conditions and the woundsallow entry of the virus. This hair loss givesaffected bees a shiny, greasy appearance. OnceCBPV has gained access to the bee’s blood(haemolymph) it rapidly spreads to and multiplieswithin many tissues including the nervous system.Severe cases of CBPV are rare: there is no regularseasonal pattern to its occurrence. At the height ofthe summer season, severely affected coloniesmay suddenly decline, leaving the queen with fewworkers on neglected combs. (However, recoveryis possible if conditions improve). Symptoms ofparalysis occur when local events confine adultbees to their colonies at times of the year whenthey would normally be foraging. These eventsoccur at irregular intervals during the usuallyactive season of bees for a variety of reasons, bothnatural (e.g. a sudden failure of nectar flows) andartificial (e.g. when too many colonies are kept forthe available forage).

Methods of transmission of CBPV

• This virus spreads most readily when bees areconfined and have unusually prolonged bodilycontact. This occurs in periods of inclementweather or due to overcrowding.

• The faeces of infected bees contain high levelsof infective virus and oral-faecal transmissionhas been reported.

Treatment and control of CBPV

In crowded conditions, CBPV will spread morerapidly because bees will be in greater contact

with each other – increasing the chances thatbees will rub up against one another therebypulling out hairs from their abdomens. This wouldleave an open wound on the bee where the virus isfree to enter and worsen or cause infection inhealthy bees. As a result we recommend that instrong colonies that show signs of CBPV,beekeepers should ensure that there is plenty ofroom by adding supers or an extra brood box.CBPV rarely causes severe problems and if acolony cannot combat the virus through its ownmeans then the only method of control is to re-queen a colony with a queen from a lesssusceptible strain.

Diagnostic Services at the NBUThe diagnosis of any notifiable pests and diseasessuch as the detection of foulbroods, and suspectedexotic pests is a statutory service, provided by theNBU at no charge to the beekeeper. However, wealso offer a chargeable adult bee disease diagnosisservice. This provides fast, reliable diagnostics toallow you to monitor your colonies for the causativeorganisms of those adult bee diseases discussedin this leaflet.

To detect the causes of adult diseases it isnecessary to analyse samples of bees. We havedeveloped methods and expertise that will detecteven very low levels of disease and give you anidea of the extent of the infection so that you arebetter able to decide on the appropriate course ofaction. If you are interested in using this service,you will need to submit 30 adult bees to the NBU.A report, together with advisory notes asappropriate, is sent by return post. Full detailsand price lists are available from the BeeBasewebsite (https://secure.fera.defra.gov.uk/beebase/index.cfm?pageid=158). Our standard test usesmicroscopic techniques for the presence ofAcarine, Nosema spp. and Amoeba. Molecularpathogen screening (using TaqMan® PCR) cantest for viruses and/or N. apis and N. ceranae.Please ask for more details.

Viruses

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Useful addresses

Fera National Bee Unit (NBU)The Food and EnvironmentResearch AgencyNational Bee Unit, Sand Hutton,York, North Yorkshire, YO41 1LZ Tel: 01904 462510Fax: 01904 462240Email: [email protected]: www.nationalbeeunit.com

Office of the Chief Veterinary OfficerWelsh Assembly Government OfficerHill House Picton TerraceCarmarthen SA31 3BSTel: 01267 245 007Web: www.wales.gov.uk

Scottish GovernmentPentland House47 Robbs LoanEdinburghEH14 1TYTel: 0131 244 6178Web: www.scotland.gov.uk

Science and Advice for ScottishAgricultureSASA, Roddinglaw Road Edinburgh EH12 9FJTel: 0131 244 8890Fax: 0131 244 8940 Email: [email protected]: www.sasa.gov.uk

Chemicals LAIFIndustria Bio-chimicaVia dell'artigianato, 1335010 Vigonza (PD)ItalyWeb: www.beekeeping.org/chemical-laif/index.htm

World Organisation for AnimalHealthOffice International des Epizooties(OIE)Web: www.oie.int

Department of Agriculture andRural DevelopmentNorthern Ireland (DARDNI)Dundonald House, Belfast BT4 3SB,Northern IrelandTel: 02890 24488Web: www.dardni.gov.uk

Defra Veterinary MedicinesDirectorateWoodham LaneNew HawAddlestoneSurreyKT15 3LSTel: +44 01932 336911Web: www.vmd.gov.uk

British Beekeepers’ Association(BBKA)(county and local beekeepingassociations) National AgriculturalCentre, Stoneleigh Warwickshire,CV8 2LG Tel: 08718 112282Web: www.bbka.org.uk

Scottish Beekeepers’ AssociationWeb: www.scottishbeekeepers.org.ukEmail:[email protected]

World Organisation for AnimalHealthOffice International des Epizooties(OIE)Web: www.oie.int

Office of Public Sector Information (European Community and UKLegislation) Web: www.opsi.gov.uk/

Ulster Beekeepers’ AssociationWeb: www.ubka.org

Bee Farmers’ Association (BFA)Web: www.beefarmers.co.uk

International Bee ResearchAssociation(library and beekeeping informationservices)Unit 6, Centre CourtMain Avenue Treforest CF37 5YRUKTel: 02920 372409Web: www.ibra.org.uk

Welsh Beekeepers’ AssociationWeb: www.wbka.com/

Vita (Europe) Ltd21/23 Wote StreetBasingstoke Hants RG21 7NETel: +44 (0)1256 473175 Fax +44 (0)1256 473179Web: www.vita-europe.com

MAQS NOD Europe Ltd5 St Paul’s Square Old Hall StreetTel: +44 (0)1630 655722 Email: [email protected]: www.nodglobal.com

Bayer (UK and Ireland) LtdWeb: www.bayer.co.uk

BiovéLaboratoires BiovéRue de LorraineP.O.Box 4562510 ArquesFranceWeb: www.beekeeping.com/biove

BioVetTel: +41 (0)62917 5110Email: [email protected]: www.biovet.ch/ea/Imkerei/thymovar.html

European Community and UKLegislationThe Stationery Office51 Nine Elms LaneLondonSW8 5DRTel: +44 0870 600 5522Web: www.hmso.gov.uk/stat.htm

Bee Disease Insurance Ltd (BDI)Registered OfficeNational Beekeeping Centre, NACStoneleigh ParkWarwickshireCV8 2LGTel: 08718 112337Web: www.beediseaseinsurance.co.uk

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References

A number of references were used in the development of this advisory leaflet and/or may be useful as furthersources of information:

Chen Y.P., Siede, R. (2007) Honey bee viruses Adv Virus Res. 70:33-80.

Martin, S.J., Highfield, A.C., Brettell, L., Villalobos, E.M., Budge G.E., Powell M., Nikaido S., Schroeder D.C. (2012)Global honey bee viral landscape altered by a parasitic mite. Science. Jun 8; 336(6086):1304-6.

Morse, R., Flottom, K. (editors) (1997) Honeybee pests, predators and diseases. A. I. Root, Medina. Ohio, USA.

OIE (2008) Acarapisosis of honeybees. OIE Terrestrial Manual Chapter 2.2.1(http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.02.01_ACARAPISOSIS.pdf).

OIE (2008) Nosemosis of honeybees. OIE Terrestrial Manual Chapter 2.2.4 of(http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.02.04_NOSEMOSIS.pdf)

Special issue on diseases of the honeybee (2010) Journal of Invertebrate Pathology Volume 103, Supplement,Pages S1-S132 (January 2010).

Webster, T.C. & K.S. Delaplane (editors) (2001) Mites of the honeybee. Dadant & Sons, Hamilton, Illinois, USA.

Acknowledgements

Leaflet revised by Gay Marris, Mike Brown, Jason Learner, Ivor Flatman, Jack Wilford, Giles Budge, RuthGrant and Linda Crossley (Fera). Photographs Fera NBU. Leaflet designed by: www.spacecreative.co.uk

References and Acknowledgements

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Notes

21

Notes

Sand Hutton, YorkYO41 1LZ, UK

Tel +44 (0)1904 462 000Fax +44 (0)1904 462 111

E-mail [email protected]/fera

BOO93/1213