Prepared by II. SHImanUki, Agricultural Research Service

Bee diseases are present throughout the United States. They are responsible for large annual losses in bees, honey, and equipment, and add greatly to the cost of production. Also, the loss of pollinating bees results in a lower yield of seed and fruit.

Bee diseases should be detected in their early stages; prompt treatment will prevent their spread. (See box on sending diseased samples for diagnosis on page 13. ) Contagious diseases spread quickly within a colony, and the crowding of colonies increases the possibility of the spread of diseases from hive to hive. When searching for disease symptoms be aware that a colony may have more than one disease.

It is especially important that the two most serious brood diseases-American foulbrood and European foulbrood-be detected early. Make routine inspections for these diseases.

Brood Diseases

To identify brood diseases, carefully examine dead brood found in the cells. The appearance of the combs may indicate which brood disease is present, but final diagnosis depends on the symptoms shown by the dead brood.

Dead brood in open cells of a comb can be seen clearly if the comb is inclined so that direct sunlight falls on the lower side of the cells. If you do not find any dead brood in the open cells, remove sunken, discolored, or punctured cappings and examine them for dead brood.

When you examine dead brood, observe its appearance and position in the cells. Note its age, color, consistency, and odor. For example, if the affected brood is unsealed in the comb then European foulbrood is suspected. If only the sealed brood is affected, and has collapsed into a ropy brown mass, American foulbrood is suspected.

Guide For Comparing Characteristics of Various Brood

Diseases of Honey Bees

Characteristics to observe

American foulbrood

European foulbrood

Sacbrood

Appearance of brood comb.

Sealed brood. Discolored, sunken, or punctured cappings.

Unsealed brood.

Some sealed brood in advanced cases with discolored, sunken, or punctured cappings.

Sealed brood.

Scattered cells with punctured cappings, often with two holes.

Age of dead brood.

Usually older sealed larvae or young pupae.

Usually young unsealed larvae; occasionally older sealed larvae.

Usually older sealed larvae; occasionally young unsealed larvae.

Color of dead brood.

Dull white, becoming light brown, coffee brown to dark brown, or almost black.

Dull white, becoming yellowish white to brown, dark brown, or almost black.

Grayish or straw-colored becoming brown, grayish black, or black; head end darker.

Consistency of dead brood.

Soft, becoming sticky to ropy.

Watery to pasty; rarely sticky or ropy.

Watery and granular; tough skin forms a sac.

Odor of dead brood.

Slight to pronounced glue odor to glue-pot odor.

Slightly to penetratingly sour.

None to slightly sour.

Scale characteristics.

Uniformly lies flat on lower side of cell.

Adheres tightly to cell wall.

Fine, threadlike tongue of dead pupae adheres to roof of cell.

Head lies flat.

Usually twisted in cell.

Does not adhere tightly to cell wall.

Rubbery.

Head prominently curled up.

Does not adhere tightly to cell wall.

Lies flat on lower side of cell.

Rough texture.

Brittle.

Honey Bee Sacbrood Disease

Cause

Sacbrood is caused by a filterable virus. This virus is so small that it cannot be seen even with the aid of a light microscope.

Effect

Sacbrood rarely wipes out a colony of bees or becomes a serious menace to beekeeping. The disease affects both workers and drones. Pupae are killed occasionally, but adult bees are immune.

It is important for you to recognize sacbrood and distinguish it from the more serious foulbrood diseases. For a comparison of brood disease characteristics see the guide below.

Sacbrood is most common during the first half of the broodrearing season. The disease often goes unnoticed because it affects only a small percentage of brood.

Symptoms

In sacbrood, death usually occurs after the cells are first sealed. The disease rarely reaches the serious stage in which the "pepperbox" pattern becomes evident.

The larvae gradually change from pearly white to dull yellow or gray, and finally to black.

The head of the larva is the first part of the body to change color. It becomes black. (See fig. 6. ) The larva dies in an upright position.

When you remove diseased larvae from their cells and examine them, you will observe that the contents of the larvae are watery and the skin is tough and forms a sac. Hence the name: sacbrood.

The scale is gondola shaped; both the head region and posterior bend toward the center. Sacbrood scales are rough and brittle, and they loosely adhere to the cell walls.

Spread

Very little is known about the transmission of sacbrood. However, experiments employing a suspension made from diseased larvae indicate that the disease can be spread to healthy larvae through contamination of larval food.