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Foul brood disease of honey bees:recognition and control

AFB ropiness test

Honey bee colonies are subject to a number of diseases that affect their brood. This leaflet describesthe recognition and control of the two most serious of these, American foul brood and European foulbrood, along with other common but less serious brood disorders.

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Honey bees and disease

Honey bees play a vital role in the environment bypollinating both wild flowers and many agriculturalcrops as they forage for nectar and pollen. The valueof such crops grown in the UK is estimated at billionsof pounds annually - and this is in addition toproduction of honey and beeswax worth millions ofpounds. The essential and valuable activities of beesdepend upon beekeepers maintaining a healthypopulation of honey bees.

Fig 1 Honey bee colonies pollinating Oil SeedRape

As with other forms of livestock, honey bees aresubject to a range of harmful diseases. Some ofthese affect adult bees, others affect immaturestages of the bees’ development (larvae andpupae) and these are referred to as brooddiseases. There are several such brood diseasesthat affect honey bee colonies in the UK. Theseinclude the two extremely serious and infectious

foul brood diseases together with a range ofcommon and less harmful disorders.

Foul broodThe term ‘foul brood’ covers two diseases of thehoney bee larvae, one known as American foulbrood (AFB), and the other European foul brood(EFB). The names bear no relation to thegeographical distribution of the diseases: bothoccur in the British Isles and the damage done bythem annually to our beekeeping industry isconsiderable. American foul brood is consideredthe most destructive brood disease in GreatBritain. However, European foul brood is currentlythe most widespread, and where it occurs it oftenspreads rapidly and is difficult to eradicate unlessprompt measures are taken.

Minor brood diseasesThere are several other brood diseases anddisorders that, although much less serious thanfoul brood, are extremely widespread. It isessential that beekeepers are able to recognisethese and distinguish them from foul brood.

VarroosisInfestation of honey bee colonies by the parasiticmite Varroa destructor is the subject of a separateCSL/MAFF leaflet, Managing Varroa.

Beekeeper responsibility

All colonies in the UK are at risk of contracting foul brood. If disease occurs but is not detected andcontrolled, the infection will normally spread quickly through the apiary and into adjacent apiaries belonging toother beekeepers. However if the infection is spotted at an early stage, no further spread is likely to occur.

Beekeepers have a responsibility to ensure that their bees are healthy and that they are not unwittinglyspreading any infection through their beekeeping practices.

You should be familiar with the signs and causes of the diseases that may affect your bees, the action to takeif foul brood is suspected, and the measures you should take to help keep your colonies healthy andproductive.

The Bee Inspectors from the CSL National Bee Unit (NBU) cannot examine all colonies of bees each year,and it is therefore essential in the control of foul brood for you to regularly inspect your own colonies for signsof brood disease. If you suspect foul brood, you must contact the NBU for assistance. It is also very goodpractice to inform other local beekeepers of the problem so that they can check for signs in their own bees.

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10 RULES FOR FOUL BROOD CONTROL

1. Make sure you are familiar with the signs and

causes of foul brood and other brood

disorders.

2. Inspect your colonies every spring and

autumn, specifically to check for brood

disease. If you are unsure, seek expert advice.

3. Never transfer combs between colonies, or

divide colonies, without first checking for

signs of brood disease.

4. Never bring colonies, combs or beekeeping

equipment into the apiary unless you are sure

that they come from a disease-free source.

5. Never buy old combs. Always sterilise

second-hand hives by thoroughly scorching

with a blow lamp before use.

6. Control robbing in the apiary. Never leave

combs or honey exposed to robbing bees.

Never feed honey from another source to your

bees.

7. If a colony of bees dies out at any time, seal

the hive to prevent the remaining stores being

robbed out, pending examination of the brood

combs for signs of disease.

8. If any colony appears not to be thriving, and

the reason is not already known, examine the

brood for signs of disease.

9. Be suspicious of stray swarms. Hive them on

foundation rather than drawn comb, and

inspect them for disease once they have

become established.

10.Regularly and systematically replace old

brood combs in the apiary by melting them

down and replacing them with frames fitted

with foundation.

UK BEE DISEASE LEGISLATION

Both AFB and EFB are subject to statutory controls inthe UK. The Bee Diseases Control Order 1982empowers the appropriate agriculture departments ofGreat Britain to take measures to control bothdiseases. Beekeepers should be familiar with theprovisions of the Order (SI 1982 No 107), copies ofwhich are available from HMSO. Websitehttp://www.hmso.gov.uk/

Any beekeeper in England or Wales who suspectsthe presence of either AFB or EFB in a colony forwhich they are responsible is legally required either tocontact the Central Science Laboratory National BeeUnit (NBU) to have the colony officially examined, orto submit a suspect disease sample for analysis.Beekeepers elsewhere in the UK should contact thelocal office of the relevant government agriculturedepartment.

The National Bee Unit operates an apiary inspectionprogramme in England and Wales. CSL BeeInspectors inspect bee colonies for foul brood, free ofcharge. When disease is suspected, a sample istaken for laboratory analysis and a Standstill Notice isissued, prohibiting the removal of bees andequipment from the apiary. If foul brood is confirmedan inspector returns to carry out the necessarydisease control measures. For further information,see the CSL/MAFF/NAW leaflet Statutory proceduresfor controlling foul brood (PB3054).

Further details about the National Bee Unit and itsadvisory and training services are given at the end ofthis leaflet.

Fig 2 Bee disease recognition training

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How to examine a honey bee colony for brood disease

• Wear full protective clothing and have a smokerwell lit.

• Keep the colony subdued with smoke.

• Remove the hive roof and place it on the ground bythe hive.

• If there are supers on the hive, remove them andplace them on the upturned roof, keeping themcovered to prevent robbing.

• Remove any queen excluder and examine theunderside for the queen. If she is present return herto the colony.

Fig 3 Opening the hive for disease inspection

• Where two boxes are used for the brood nestexamine the bottom one first.

• Remove the outside comb, which is unlikely tocontain brood, and lean it against a front corner ofthe hive - you will then have room to work.

• Take each comb in turn, and holding it by the lugswithin the brood chamber, give it a sharp shake.This will deposit the bees on the bottom of the hivewithout harming them, the queen or brood.

Fig 4 Shaking adult bees from the comb intothe hive

• Any bees on a comb may be concealing infectedbrood from the beekeepers’ view. On combs freefrom bees, any abnormality is easily spotted

• Examine the brood, both sealed and unsealed,quickly but carefully, for any signs of abnormality -such as discoloured larvae or perforated cappings.

• Look for AFB scales (see page x) by holding thecombs towards the light and scanning the bottomwalls of any open cells

Fig 5 With bees removed the brood is clearlyvisible

• Look inside any sealed cells with abnormal lookingcappings after opening the cell with a corner of thehive tool.

• To establish the consistency of any dead remainspresent, probe these with a matchstick. Dispose ofthe used matchstick in the smoker.

• Continue until you have examined all the broodcombs; then reassemble the hive.

• If you suspect EFB or AFB may be present,contact the NBU immediately for assistance(see contacts information for details).

Fig 6 Examining comb for scales

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HEALTHY BROOD

All beekeepers should be familiar with theappearance of healthy worker brood, so thatthey can recognise abnormalities, which mayindicate the presence of foul brood or otherbrood diseases.

• The queen lays eggs at the base of cells in thebrood nest. These hatch after three days anddevelop into tiny translucent larvae lying at thebase of the cell in a bed of milky brood food.

Fig 7 Eggs and young larvae

• After six further days of development, the larvaehave increased in size to almost fill the base ofthe cell.

• Healthy larvae are pearly-white in colour. Theylie in a distinct ‘C’ shape, with the head and tailcurled towards one another.

• The body of the larva can be seen to be dividedalong its length into a series of segments.

Fig 8 Healthy larvae shortly before sealing

• When larvae are nine days old, the cell openingis sealed by adult bees with a cap of wax, anddevelopment into an adult bee occurs inside thesealed cell.

• The wax cappings on healthy worker brood varyin colour from very light to dark brown, and theyare dry looking and slightly convex.

• Drone brood can be distinguished from workerbrood by its larger cells and domed cappings.

Fig 9 Sealed healthy brood

• A good brood pattern, with very few empty cellswithin patches of brood suggests that the queenis laying well and nearly all the larvae aredeveloping normally.

• Even where the brood pattern is morehaphazard, as results from an old or failingqueen for instance, the individual larvae and cellcappings should still have a normal appearance.

Fig 10 Healthy brood in all stages

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AMERICAN FOUL BROOD

CauseAmerican foul brood is caused by a spore-formingbacterium called Paenibacillus larvae subspecies.larvae. Young honey bee larvae become infectedwhen they consume P. larvae spores in their food.The spores germinate in the gut; bacteria thenmove into the tissues, where they multiplyenormously in number. Infected larvae die aftertheir cell is sealed, and millions of infective sporesare formed in their remains. These remains dry toform ‘scales’ which adhere closely to the cell walland cannot easily be removed by bees.Consequently brood combs from infected coloniesare inevitably severely contaminated with bacterialspores.

The spores are very resistant to extremes of heatand cold, and to disinfectants. They retain theirpowers of germination for many years in honey, inold combs kept in store, or in derelict hives, skepsor boxes.

Once a colony is infected the disease will progressuntil most of the brood is affected. The colonythen becomes unable to replace the ageing adultbee population, causing it to become weakened,and finally to die out. The disease may develop formonths before the colony succumbs, and deathmay occur at any time of the year.

SpreadThe beekeeper is the chief spreading agent of thedisease. If combs, honey or hive equipment aretransferred from an AFB-infected colony to ahealthy colony, it becomes infected. Bees robbinghoney from infected colonies also transmit thedisease. Swarms from infected colonies may alsocarry infection with them and become diseasedafter they are hived.

ControlAFB is a notifiable disease under the BeeDiseases Control Order 1982 and is subject toofficial control by a programme of apiaryinspections and compulsory destruction ofinfected colonies. For confirmation of AFB asample (eg brood comb, suspect larvae in plastic

tube) is sent to the NBU laboratory where larvalremains are examined microscopically for thepresence of the causative bacteria.

Infected colonies are destroyed by burning underthe supervision of a bee inspector. The bees arekilled, and together with the combs are burned in adeep pit (Fig 11).

Hives and appliances can be sterilised bythoroughly scorching them with a blow lamp.Gloves, overalls, footwear and the smoker arewashed in hot soapy water.(Fig 12).

Methods of control of AFB using antibiotics thatare used in some overseas countries are noteffective, as they suppress signs of the diseasewithout eradicating it, and they are not permitted inthe UK.

Fig 11 Destruction of AFB infected colony

Fig 12 Sterilisation of hive boxes

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Signs of American foul brood

• AFB affects only sealed brood. When infectedlarvae die within the sealed cell, the appearanceof the cell cappings changes.

• Cappings become sunken and perforated whenadult bees nibble holes in them. Theseperforations tend to be jagged and irregular inshape.

• Some cappings may become moist or greasylooking and slightly darker in colour than othercells.

Fig 13 AFB – perforated cappings

• At first only very few cells may show signs ofdisease, and the colony will appear normal inother respects.

• Eventually much of the sealed brood willbecome affected by the disease, causing apatchy or ‘pepper pot’ brood pattern. There maythen be an unpleasant smell.

• At the sunken capping stage the dead larvalremains are light to dark brown in colour, andhave a slimy consistency.

Fig 14 AFB – “pepper pot” brood

• If a matchstick is inserted and slowly withdrawn,the remains can be drawn out in a brown,mucus-like thread or ‘rope’ 10-30mm long. Thisis called the ‘ropiness’ test and is a reliable testfor AFB.

• The ropy condition is followed by a tacky stageas the larval remains in the cell gradually dry upand the colour changes to dark brown.

• The proboscis of dead pupae may sometimesremain intact, protruding upwards from thebottom edge of the cell.

Fig 15 AFB ropiness test

• Further drying leads to the final stage, which is avery dark brown, rather rough scale lying on thelower side of the cell and extending from justbehind the mouth of the cell right back to thebase.

• The scales can be detected if the comb is heldfacing the light: they reflect the light from theirrough surfaces and can easily be seen, evenwhen their colour is almost the same as thecomb itself.

Fig 16 AFB scales in comb

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EUROPEAN FOUL BROOD

CauseEuropean foul brood is caused by the bacteriumcalled Melissococcus plutonius. The bacteriamultiply in the mid-gut of an infected larva,competing with the larva for its food. They remainin the gut and do not invade the larval tissue;larvae that die from the disease do so becausethey have been starved of food. This normallyoccurs shortly before their cells are due to besealed. Subsequently other species of bacteriamay multiply in the remains of dead larvae as‘secondary invaders’.

Progression of the diseaseThe development of the disease within a colony iscomplex, and still not fully understood. It appearsthat infection can develop over a period of monthsor years, debilitating but not killing the colony.During this time, signs of the disease may becomemore or less severe, or disappear altogether.Frequently there is a seasonal pattern, with signsbecoming most obvious in late spring.

This is thought to be because when there aremany larvae relative to the number of nurse bees,larvae tend to receive less brood food overall, andthose infected with EFB are more likely to sufferfrom starvation. At other times, larvae that areinfected but receive an abundance of brood foodmay survive the infection, and develop into healthyadult bees. However, when such larvae pupate,they void their gut contents into the cell,contaminating the comb with millions of infectivebacteria. Eventually the disease is likely to reachthe stage where a high proportion of the brood isaffected and the colony will be weakened andultimately killed.

SpreadThe beekeeper is the chief spreading agent of thedisease. If combs, honey or hive equipment aretransferred from an EFB infected colony to ahealthy colony, it is likely to become infected.Bees robbing honey from infected colonies alsotransmit the disease. Swarms from infectedcolonies may also carry infection with them andbecome diseased after they are hived.

DiagnosisEuropean foul brood cannot be reliably identifiedvisually, as the disease signs can easily beconfused with various other brood abnormalities.A sample brood comb is sent to the NBUlaboratory where larval gut contents are examinedmicroscopically for the presence of the causativebacteria (Figures 17 & 18.)

ControlEFB is a notifiable disease under the BeeDiseases Control Order 1982 and is subject toofficial control by the examination of colonies forsigns of disease and compulsory treatment ordestruction of diseased colonies. Weak coloniesand colonies with a high proportion of diseasedbrood are destroyed, as with American foul brood,but lightly diseased colonies may be treated withan antibiotic. Treatment must be carried out onlyby an Appointed Officer under the Order, usingdrugs officially dispensed following confirmation ofEuropean foul brood in a disease samplesubmitted for diagnosis at an approved laboratory.

Fig 17 & 18 Laboratory diagnosis

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Signs of European foul brood

• EFB affects mainly unsealed brood, killing larvaebefore they are sealed in their cells.

• The EFB infected larva moves inside its cellinstead of remaining in the normal coiled positioncharacteristic of a healthy larva of the same age.

• When it dies it lies in an unnatural attitude -twisted spirally around the walls, across themouth of the cell or stretched out lengthwaysfrom the mouth to the base.

Fig 19 EFB affected unsealed brood

• The dead larva often collapses as though it hadbeen melted, turning yellowish-brown andeventually drying up to form a loosely attachedbrown scale.

• The gut of infected larvae may be visible throughthe translucent body wall of the larvae. It has acreamy white colour caused by the mass ofbacteria living within it.

Fig 20 EFB - twisted and discoloured larvae

• When a high proportion of the larvae are beingkilled by EFB, the brood pattern will often appearpatchy and erratic as dead brood is removed bythe bees and the queen lays in the vacant cells.

• A very unpleasant odour may sometimesaccompany severe EFB infection, depending onthe presence of certain other species of bacteriain the remains of dead larvae.

Fig 21 EFB – severe infection and patchy broodpattern

• A minority of infected larvae may die after the cellis sealed. In such cases, there may be sunkenperforated cappings resembling AFB infection.However, the cell contents although brown andsticky can not be drawn into a ‘rope’ as with AFB.

• Where larval remains dry to form scales, theseare variable in colour, loose within the cell andsomewhat rubbery, unlike the hard black firmlyattached scales of AFB.

Fig 22 EFB – dead brood with scales

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Controlling an outbreak of foulbrood in your colonies

If you keep bees for long enough, it is very likelythat you will someday have to deal with anoutbreak of EFB or AFB in your colonies. Whenthis happens, your Bee Inspector will visit youseveral times to help bring the infection undercontrol - first inspecting your colonies for signs ofdisease, then treating or destroying infectedcolonies, and later returning to make sure thatsigns of disease have not reoccurred in the apiary.Please see leaflet Statutory procedures forcontrolling foul brood.

However, you have an equally important role inbringing the disease under control. This entailsusing some common-sense methods to avoidspreading the infection between colonies, andmaking sure that any new cases of disease arerecognised before they can spread to othercolonies.

Both EFB and AFB are infectious diseases, andcan spread without the intervention of thebeekeeper by the natural processes of robbing,drifting etc. Despite this, unfortunately in practicethe main agent of spread is the beekeeper, as hemoves combs, brood, bees and other diseasecarrying materials between colonies.

If careless, an infection that may only affect onecolony in the apiary at the start of the beekeepingseason, may easily affect all the colonies by theend. Conversely, however, experience has shownthat even very severe outbreaks of foul broodaffecting many colonies in large beekeeping outfitscan be successfully brought under control so longas cases of foul brood are found and dealt-withfaster than new cases are allowed to develop.

Key strategies for controlling anoutbreak of foul brood in your bees

1. Learn to recognise the signs of foul brood.

This is a skill that takes a little time andpractice to acquire. Start by working with yourbee inspector, as he inspects your bees. Hewill be glad to point out the signs thatdistinguish diseased and healthy brood. Then

every time you inspect your bees, make apoint of always checking the brood for signs ofdisease. Your aim should be to spot onediseased larva in a comb of several thousand.You can send individual suspect larvae to theNBU for diagnosis using larval tube samplingkits (available from your bee inspector).

2. Use quarantine systems to avoidspreading disease

When colonies with signs of foul brood havebeen found and dealt with, there is still asignificant risk that other colonies may beinfected but not yet showing signs of disease.Many beekeepers have found 'quarantinesystems' to be very effective in minimising thespread of infection between colonies while afoul brood outbreak is brought after control.These will also help minimise the scale of anynew outbreaks that may subsequently occur.

For instance:

• Colony quarantine - avoid moving anycombs, bees or equipment from onecolony to another. It will be necessary tomark super frames and boxes so thatthey can be individually identified andreturned to the same colonies afterextraction. This is the most effectivequarantine system, and the mostappropriate for colonies that are atparticular risk - such as those that havebeen previously treated, and those thathave had close contact with infectedcolonies - but involves significant effort tocarry out on a large scale.

• Apiary quarantine - avoid moving anybees, combs or equipment betweenapiaries, but allow some movement (e.g.super combs) within the apiary. This willnot prevent spread within the apiary butinvolves less work than colony quarantineto implement on a large scale and helpsprevent moving disease betweenapiaries.

• 'Isolation apiaries' - where an EFBoutbreak extends between severalapiaries managed by a single beekeeper,it can often be advantageous to move allknown infected colonies, and other

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colonies believed to be at particular riskto a single apiary (under licence from theNBU). This keeps to a minimum anycontact between diseased and healthycolonies, and makes it easier to operatequarantine systems appropriate to thelevel of risk in each apiary.

• Disinfecting equipment - where it isnecessary to move items betweencolonies, treat them to reduce the risk ofspreading disease. Wooden hive partscan be made safe by scorching with ablowlamp. Hive tools, gloves, the smokeretc. can be soaked in or scrubbed with astrong solution of washing soda.

3. Transfer colonies to new comb

The pathogens responsible for both AFB andEFB can exist in a colony's combs for longperiods and remain capable of causingdisease to develop. This is particularly true ofcolonies which have been treated against EFBwith antibiotic. A significant proportion of suchcolonies can suffer a reoccurrence of diseasewithin a year or so as a result of live bacteriaremaining in the colony after treatment.

Any method that removes such contaminated

comb from colonies and replaces it with newcomb will be helpful in reducing the risks ofdisease. However, the more rapid andcomplete the transfer, the more effective itwill be.

The 'Shook Swarm' method aims tocompletely remove by transferring the colonyto entirely new combs in one operation. This isdone by shaking the adult bees into a cleanhive fitted with frames of foundation before theend of the season. The removed combs arethen destroyed by burning. Although thismethod involves significant labour andexpense, recent research at the NBUsuggests that it is extremely effective atcombating EFB.

Many beekeepers have found that colonieswhen treated as shook swarms are capable ofquickly building up to gather a good crop ofhoney, and that the reduced risk ofreoccurrence of EFB makes it a sensiblestrategy for dealing with colonies that havebeen treated for EFB, and other coloniesthought to be at particular risk.

For further details of methods that can be used tohelp control foul brood contact the National BeeUnit or your local bee inspector.

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COMMON BROOD DISORDERS

In addition to the foul brood diseases, there arealso less serious honey bee brood disorders suchas sacbrood, chalkbrood, bald-brood, layingworkers and drone-laying queens. It is importantthat beekeepers are able to distinguish betweenthese and foul brood.

SACBROODSacbrood is a very common virus diseaseaffecting brood. In most diseased coloniesrelatively few larvae are visibly affected, and itrarely causes measurable harm to colonies.However, its signs can sometimes be mistaken forthose of AFB.

Disease signsLarvae that have died from sacbrood become likefluid-filled sacs, stretched on their backs with theirheads towards the top of their cells. Adult workerbees eventually uncap them.

Diseased larvae turn from the normal pearly-whitecolour to pale yellow and the head curls up as thebody dries to a thin, dark brown scale lying along thebottom wall of the cell. These are referred to as‘Chinese Slippers’

Fig 23 Sacbrood infected larva (cell mouthenlarged for photograph)

The scale of a sacbrood infected larva has adistinctive gondola shape and is easily removed inone piece from its cell using a matchstick

Treatment and controlThere is no specific treatment for sacbrood. Whenmuch of the brood is obviously affected, the queenshould be replaced by one from a colony showing nosigns of the disease. Combs can be re-used; any

sacbrood virus present on them becomes non-infectious within a few weeks.

Fig 24 Sacbrood “Chinese slipper” (removedfrom cell for photograph)

VARROOSISColonies that are severely infested with varroamites (Varroa destructor) frequently suffer fromdeath of brood. This is normally most apparent incolonies that are very severely infested, especiallythose that are collapsing from the infestation inpoorly treated or unmanaged colonies. Thedamage results not from the mites themselves,but from viruses that are triggered by theinfestation or, in the case of collapsing colonies,from the bees failing to care adequately for theirbrood.

Disease signsSigns of damage to brood in varroa infestedcolonies can be very variable. Most commonlysealed brood appears affected, with dead anddiscoloured brood in various stages belowperforated cappings. The larval remains may befirm or watery, but never ropy (as with AFB).Close examination will reveal numerous varroamites in floor debris, brood cells and on adult bees.

Fig 25 Varroa – comb from collapsing colony

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CHALKBROODChalkbrood is an extremely common brooddisease caused by the fungus Ascosphaera apis.The thread-like, vegetative growths (‘hyphae’) ofthe fungus invade the body tissues of infectedlarvae, killing them after they have been cappedover in their cells.

Disease signsAdult bees usually tear down the brood cell cappingsto remove the dead larvae. These appear as hard,chalky-white or mottled grey remains (‘mummies’)lying along the length of the cell.

Infected larvae often take on the hexagonal shape ofthe cell itself before shrinking in size, at which pointthe bees are able to remove them from the comb.They are often noticeable on the hive floor or at thehive entrance.

Fig 26 Chalkbrood infected brood

The spread of chalkbroodLarvae affected by chalkbrood may release millionsof spores that all have a sticky coating, enablingthem to adhere to combs and to adult bees. Theseare the dormant phase of the fungus and can remaininfectious for three years or more.

Fig 27 Chalkbrood “mummies” on a hive floor

Both the transfer of combs by the beekeeper and thedrifting of bees transmit chalkbrood spores betweencolonies.

Signs of chalkbrood are probably present in themajority of colonies at some time, and spores ofA. apis can be detected even in apparentlyunaffected colonies. However, it is rarely a seriousdisease, and the effect on most colonies is slight.Chalkbrood is most likely to be serious in coloniesthat are finding it difficult to care adequately fortheir brood, and is therefore most prevalent inweak colonies and during early spring.

Treatment and controlThere are no specific treatments for chalkbrood.The most effective control results from avoidingthe conditions favourable to its increase bymaintaining strong and vigorous colonies, andbees that show marked hygienic behaviour. Insevere cases, re-queening with a queen from achalkbrood-free colony is recommended.

BALD BROODNormally pupae are sealed in their cells underwax cappings until they are ready to emerge asadults. Colonies with bald brood may have smallpatches of live and normal looking pupae in cellsthat are incompletely capped. The partial cappingfrequently has a raised lip that protrudes from thecomb.

Fig 28 Bald brood

The cause of bald brood is not always clear;however the most common reason is infestation ofbrood combs by wax moth larvae. These canoften be found tunnelling below the surface of thecomb close to patches of bald brood.

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DRONE BROOD IN WORKER CELLSThe characteristic domed cappings of sealeddrone brood are present in virtually all coloniesduring the summer months on areas of dronecomb, usually situated at the edge of the broodnest. However, there are common abnormalitiesthat can cause drone brood to be reared in workercells along with, or in place of, worker brood. Suchdrone brood is usually very irregular; cappedpupae are interspersed with either vacant cells orcells containing larvae at every stage ofdevelopment. There are two possible causes - adrone-laying queen or laying workers. Beekeepersoften confuse these conditions with serious brooddiseases.

Drone-laying queenWorker bees develop from eggs that have beenfertilised, before they are laid, by sperms stored inthe queen’s sperm sac (spermatheca). If the supplyof sperm becomes exhausted, only unfertilised eggsare laid, which develop into drone brood. Hence,queens may become drone-layers in later life orearlier if they have not properly mated. Such queensshould be replaced with one of proven fertility.

Fig 29 Domed cappings of drone brood inworker cells

Laying workersWhen colonies lose their queen and have noyoung worker brood from which to rear areplacement, the workers may develop functionalovaries and begin to lay eggs. These eggs, beingunfertilised, develop into drones; the signs aresimilar to those of the drone-laying queen, exceptthat the brood pattern is often less compact. Also,there may be several eggs present in some cells,

often on the walls as well as at the bottom of thecell. Colonies with laying workers are very difficultto requeen, and are usually in poor condition. It isgenerally advisable to unite them with a strongcolony, or to destroy them.

Chilled broodSometimes relatively large areas of brood in allstages die at the same time and turn very dark incolour. This is usually diagnosed visually as‘chilled brood’. However, even young larvae cansurvive for several hours at temperatures well

below the brood nest heat of 35° C. It is probable,therefore, that ‘chilling’ of brood is the result ofbrood becoming isolated from the adult bees andbeing neglected by them. As a result the brooddies from a combination of starvation andprolonged low temperatures. No pathogenicorganism is responsible.

Examining colonies in cold weather should notcause chilled brood. Keeping colonies in thrivingcondition with ample bees to cover and nurture thebrood can prevent chilled brood.

Diseases of uncertain originEggs, larvae and pupae sometimes die forreasons unconnected with infectious disease, andthe cause of the death is often difficult toestablish. A patchy brood pattern might be theresult of poor egg-laying by the queen, or causedby a genetic defect in some of her eggs,preventing them from hatching or developing fromlarvae into adults. Usually the workers quicklyremove the dead brood. Brood death of this kindmay happen in many colonies, however, thenumbers of abnormal eggs or larvae are probablyso low that they are removed by the bees beforethe beekeeper even notices.

If a genetic defect or a faulty queen appears to bethe cause of a brood disorder then replacing thequeen with another is the most effective course ofaction.

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SUMMARY OF BROOD DISEASE SIGNS, CAUSES AND CONTROL

SIGNS OF DISEASE CONTROL

Normal brood Uncapped: Pearly white, ‘C’ shaped larvae.

Capped: Uniform brown colour, domed cappings.

None required.

American foulbrood(Paenibacillus larvaesubspecies. larvae)

Affects only sealed broodsunken concave cappings, uneven brood pattern,‘pepper pot’ or mosaic pattern, scales on bottomwalls of open cells, brown decomposing larvae that‘rope’ using matchstick test, moist dark perforatedcappings.

Notifiable disease

A CSL Bee Inspectorburns infected coloniesand the hives aresterilised by scorching.

European foulbrood,(Melissococcusplutonius)

Affects mainly unsealed brood.Infected larvae discoloured yellow-brown lying inabnormal positions in cell with ‘melted’ appearance.

Some dark sunken cappings may be present, butcell contents will not form a ‘rope’.

Notifiable disease

Lightly infected coloniesare treated by a CSL BeeInspector with antibiotic.

Severe cases of EFB aredestroyed as with AFB.

Chalkbrood(Ascosphaera apis)

Affects only sealed brood.

Perforated cappings over cells containing hardwhite or mottled grey chalk like remains(‘mummies’).

No specific treatment.

Keep strong colonies.Requeen severelyaffected colonies.

Sacbrood(sacbrood virus)

Affects only sealed brood.

Perforated cappings. Larvae become yellow-brownfluid filled sacs (‘Chinese slipper’).

Watery contents will not form ‘rope’.

No specific treatment.

Requeen severelyaffected colonies.

Bald brood Abnormal cell cappings over sealed brood. Affectedcells have round hole in capping sometimes with aslight protrusion. Pupae have normal appearance.

Signs of wax moth larvae may be visible in comb.

No specific treatment.

Control wax mothinfestation.

Drone laying queenor laying workers

Domed drone cappings over worker cells.Abnormally small drone pupae within cells. May bemultiple eggs per cell. Unsealed brood may beneglected and dying.

Replace drone layingqueen. Unite colony withlaying workers to anothercolony.

Chilled brood Dead brood usually present in all stages. Unsealedbrood turns very dark brown or black in colour.

Avoid conditions thatprevent bees being ableto care for brood.

Varroa infestation Signs vary. Sealed brood may be partiallyuncapped, dead pupae discoloured brown or black,watery or firm, but never ropy.

Control varroa infestationto low levels usingappropriate treatment.

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FURTHER INFORMATION

What to do if you suspect foul brood

1. Close the hive

2. Reduce the size of the entrance and take any other steps necessary to prevent the hive being robbedby other colonies

3. Disinfect gloves and beekeeping equipment before examining other colonies

Either:

a) Contact the NBU to arrange a visit by your local bee inspector

b) Send a whole comb containing diseased brood wrapped in several layers of paper and sealed in acardboard box so that it can not leak honey in transit to the NBU, with a note stating your name andaddress, the location of the apiary and the identity of the affected hive.

4. You must not remove any hives, bees, or equipment from the apiary until the disease, if present, hasbeen controlled.

Sterilising hives and equipment

It is very good practice to sterilise spare andempty hives routinely before re-use. This appliesparticularly to second-hand equipment and thatwhich might have been associated with foul broodinfection, but also will help to reduce the likelihoodof transmitting foul brood or other diseasesbetween colonies, if applied as part of normalapiary management.

HeatWooden hive parts can be sterilised by firstscraping off brace comb and propolis, and thenscorching with a blowlamp until the wood reachesa uniform coffee-brown colour. Particular attentionneeds to be paid to the corners and any cracks orcrevices. Such treatment will destroy the infectivestages of all the bee diseases. Alternatively, emptyhive boxes and frames can be sterilised byimmersion in molten paraffin wax heated to 150°Cfor 10 minutes.

Chemical sterilisationThere are no chemicals that have been shown tobe suitable for the sterilisation of stored combsagainst foul brood. The spores of AFB in particularare strongly resistant to virtually all sterilisingagents. Combs can, however, be sterilised to

destroy the spores of chalkbrood (and Nosemadisease of adult bees), using acetic acid vapour.In general it is better practice to melt down or burnold combs and replace them with new framesfitted with foundation.

Irradiation of equipmentEquipment such as stored supers and emptycombs which may have been associated withcolonies infected with foul brood, but do not showany disease signs, can be sterilised by gammarays from a radioisotope of cobalt. This will kill thespores of the bacteria that cause disease withoutdamage to equipment. Infected combs must notbe irradiated if scales or other disease signs arepresent as these would remain indistinguishablevisually from infectious untreated disease signs.

Firms specialising in irradiation use 25 kiloGrays(kGy) to kill Paenibacillus larvae (AFB) and itsspores on combs and hive equipment. Currentlythere is no recommendation for the treatment withirradiation for Melissococcus plutonius (EFB), butit is likely that 25 kGy is sufficient to kill M.plutonius.

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The National Bee Unit

The Central Science Laboratory National Bee Unitprovides a statutory and advisory service tobeekeepers in England and Wales. It providesdiagnostic, constancy and research services toMAFF, NAW, commerce and beekeepers. TheUnit laboratories are fully compliant with theinternational Good Laboratory Practice (GLP)quality scheme to ensure a high professionalstandard. All staff are trained practical beekeepersas well as scientists, and are supported by teamsof analytical chemists and agricultural specialistsin the rest of CSL. (website addresshttp://www.csl.gov.uk)

Fig 30 Central Science Laboratory, SandHutton, York

Fig 31 Disease control co-ordination from theNBU

Further help and advice

The NBU has a bee health support service,operating in England and Wales, comprising aregional network of Regional Bee Inspectors(RBIs) managing teams of Seasonal BeeInspectors (SBIs). As well as the control of foulbrood through a programme of apiary inspections,the bee inspectors provide advice and assistanceto beekeepers on a range of bee health issuesand run training courses for beekeepers ondisease recognition and control, usually inconjunction with local beekeeping associations.For further information see contacts informationon this website.

In many areas, beekeeping associations operatelocal disease control schemes, and providepractical help and advice to members on beedisease recognition and control. Contact your localbeekeeping association for details.

Bee Diseases Insurance LtdAn insurance scheme to compensate againstlosses incurred through destruction of foul broodinfected colonies is organised by Bee DiseasesInsurance Ltd, a specialist insurance companyoperating with the aim of reducing the incidence ofthe foul brood diseases. Beekeepers can take outinsurance either individually or through their localbeekeeping association.

AcknowledgementsLeaflet written by James Morton and Michael Brown, Central Science Laboratory National Bee Unit on behalfof MAFF Horticulture and Potatoes Division.