Diseases & Pests of Apis Mellifera

American Foulbrood

Pathogen:

bacterium Paenibacillus larvae

Vegetative (growing) stage: American Foulbrood (AFB) is caused by non-infectious rod-shaped bacteria cells measuring 2.5-5 microns long by 0.5 microns wide. If larva has been infected less than 10 days, the vegetative cells are present. (Shortest possible time for symptoms to show after infection is 12.5 days, internal manifestation only prior to that.)

Spore stage: Oval-shaped infectious endospores germinate approx. 1 day after ingestion by the larvae. After germination, the bacteria multiply in the midgut & penetrate the body cavity through the gut wall. Larvae ultimately die from septicemia, an invasion of the bacteria into the blood.

Spores are resistant to heat (high & low temperatures), chemical disinfectants, and desiccation (drying action of honey that normally kills bacteria)

Spores germinate into the vegetative state after entering the larval gut & continue to multiply until larval death.

Spores can remain alive & infectious at least 35 years in honey, combs, & used equipment

Symptoms:

Odor: Foul glue pot smell. AFB was called “the stinking disease” prior to 1906.

Cappings are dark brown, usually sunken & perforated/punctured. Surface will be moist/wet rather than dry. Be alert for a single uncapped brood cell that persists after other brood cells around it have emerged

Brood pattern exhibits pepperbox symptoms (often not seen if infection is light).

Larvae change color from pearly white to dull white to tan to brown to black. Color change is uniform over the entire body. Infected larvae look melted & lie flat on the bottom side of the cell.

If larvae pupate before death, a pupal tongue is visible as a fine thread from the bottom to the top of the cell. It extends away from scale towards center of brood cell. Symptom is not always present.

Ropy test: After death, the consistency of the body gradually thickens as it dries to the scale condition (takes up to a month). When using a toothpick to remove dead brown larvae, the skin ruptures easily & gluey matter sticks to the toothpick. The sticky matter can be drawn out like a thread & can stretch up to 1 inch (2+ cm). Symptom is not always present.

Scales (dried remains) later form within a month or so as the dead larvae dry out. Each larvae produces approx. 2.5 billion spores. Scale adheres tightly to cell wall and lies uniformly flat on the lower side of cell. House bees have difficulty removing scale.

Larvae only: the name includes the word “brood” !! AFB is the most widespread, persistent, & destructive of the brood diseases, afflicting larvae of the queen, drones, & workers. Mainly worker brood. Drone brood the least.

Brood death occurs after capping, during last 2 days of larvae stage (prepupal) and first 2 days of pupae stage. Susceptibility of larvae decreases with increasing age. Larvae are no longer susceptible after 53 hours old.

Transmission:

The pathogens that cause honeybee diseases are highly host specific, therefore, there is no danger to humans from contacting infected equipment or eating honey/wax from a diseased colony.

Presence of AFB is not an indicator of poor colony management (only if you fail to detect or recognize the disease).

Strong colonies are more likely to become infected because they have a larger field force. Often occurs during nectar dearth when bees are searching for food sources & robbing. AFB is spread from colony to colony by robbing & drifting bees.

As colony weakens, it can no longer prevent robbing of the spore-containing honey.

House cleaning by bees can also spread AFB as the diseased brood cells and scales are removed. Spread by the beekeeper when feeding honey/pollen from diseased colonies or inter-changing brood combs (equalizing hives, splits, etc) among diseased & healthy colonies. Honey from an unknown source should never be fed to your bees.

The first line of defense is to detect & recognize the early symptoms disease.

Brood diseases are generally easier to detect than adult diseases. AFB can occur any time of the year that brood is present (no seasonal outbreak). Once a colony is infected, the number of infected larvae gradually increases because diseased larvae/scale serve as a spore reservoir.

Treatment:

Mix 6 oz. Terramycin (oxytetracyline HCL) & 2.5 pounds powered sugar sprinkled over tops of brood comb. This is a preventative measure to kill in vegetative state before spores are formed within the gut of the larvae When fed by workers to susceptible larva, Terramycin may also inhibit germination of the spores into vegetative state & delay vegetative growth in the larva. Terramycin can also be mixed into an extender patty (originally invented in the 1970s to treat AFB.) Terramycin is relatively unstable (breaks down quickly) in honey & syrup. Dusting also reduces the likelihood of Terramycin getting mixed into the honey. Honey contamination is greater with syrup. Cease treatment 4 weeks/28 days prior to honey flow (one reference states 45 days). Remove all honey above brood nest prior to drug feeding. Terramycin masks the disease only; it kills vegetative stage only, not the spores. AFB symptoms often reappear after antibiotic treatment stops.

Recent testing indicates resistance to Terramycin is occurring.

Other treatments:

Gamma radiation (cobalt-60), sterilization similar to that used in food services, impractical for a small beekeeper

Ethylene oxide (ETO) fumigation (MD, NC), a gaseous sterilant using heat and pressure to actually kill the spore, but a known carcinogen, used at the state level only

High velocity electron beams

Sodium sulfathiazole removed from market in 1976; not properly registered for use.

Antibiotics being considered for control of AFB: Tylan Soluble/Tylan Tartrate, & Lincomix Soluble Powder/Lincomycin HCL

Control of pathogens is a major function of propolis in the hive. It is “highly active towards Bacillus larvae” as an anti-bacterial agent. Royal jelly also inhibits bacterial growth.

LD₅₀ (number of micro-organisms that will kill 50% of larvae in a test series) of Paenibacillus larvae is 35 spores in 1- day old larvae. 1 spore is sufficient to infect a larva 1 day after egg hatch

Resistance:

Honeybee resistance/susceptibility to AFB is primarily related to the differences in hygienic behavior, which is usually strain related. The range of hereditary factors/behaviors may include the following in varying degrees:

1. Prompt uncapping of cells containing a diseased larvae- controlled by a recessive gene

2. Removal of dead larvae before it hardens into adhering scale- controlled by a second recessive gene

3. A young larvae quickly becomes resistant to infection as it ages

4. The efficiency of the adults in filtering the spores of the Paenibacillus larvae from larval food by means of their proventicular valve of the parantheca.

5. The efficiency of a bactericidal filter in the gland secretions of nurse bees when feeding brood food. These secretions serve to possibly dilute any infection in the reays part of the food.

Beekeeper Action:

Combs containing dead brood from AFB, scales, or spores are best burned

Colonies are often killed because the adults can spread the disease.

Equipment can be:

1. Immersed in a solution of 1 part lye: 10 gallons water for 10 minutes.

2. Scraped, brushed with stiff brush & soapy solution, & then scorched.

Neither of these 2 methods are 100% effective

Confirmation:

Lab Testing: Spores exhibit “Brownian movement”. Other forms of Bacillus larvae usually remain fixed & do not exhibit Brownian movement ( a wiggly/jiggly movement on the specimen slide) Must not be used as the sole determination test

Apiary inspection in the US is under the individual State’s Dept of Agriculture & their primary function (& Canada’s inspectors) is the detection & control of AFB.

Geography & Race:

AFB is found on every continent (5), but not every country.

.AFB is found in Apis cerana in India.

AFB is infrequent or absent in Apis scutellata (Africanized honeybees ).

AFB is the honeybee disease that is most likely to kill the colony, although possibly not the first year,

Primary Reference:

Collison, Clarence. 2003 What Do You Know? The A. I. Root Company. Medina, OH

References:

Graham, Joe M.-Editor. 2000. The Hive and the Honey Bee. Dadant & Sons, Inc., Hamilton, Il.

Penn State College of Agricultural Sciences.1999. Honey Bee Parasites, Pests, Predators and Diseases.

Delaplane, Keith S. 1996.Honey Bees & Beekeeping A Year In The Life Of An Apiary. University of Georgia Cooperative Extension Service

Caron, Dewey M. 1999. Honey Bee Biology and Beekeeping. Wicwas Press Cheshire, CT

Information compiled by Beekeeper Lonnie E. Campbell of The Loudoun Beekeepers Association.