Open Source Content Management

Stress Diseases

Stress diseases are maladies that strike honey bee colonies when conditions stretch the capabilities of bees to meet the needs of the colony. It is not uncommon for the busiest times of brood-rearing to be the most stressful. The three diseases covered here are European Foulbrood, Sacbrood, and Chalkbrood.

European Foulbrood

How It Spreads

European Foulbrood (EFB) is a bacterial disease caused mainly by Melissococcus pluton. This disease usually shows up in the spring and early summer, when brood rearing is at its height. It frequently disappears with a strong nectar flow. This bacterium is not spore-forming and does not form a scale that adheres to the bottom side of the cell. For these reasons, it is not nearly as dangerous or contagious as American Foulbrood.

Symptoms

Recognizing EFB is sometimes challenging, because it has highly variable symptoms. The best way to identify EFB is to note the color change of infected larvae. They change from the usual pearly white to blotchy yellow, then brown, and finally dark brown. Unlike American Foulbrood, in European Foulbrood most larvae die before their cells are capped and thus the color changes can be seen. The scale that remains is loose and easy for the bees to remove.

Diagnosis

Larvae infected with European Foulbrood die still in a "C" shape before the cell is capped:

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The larvae inside the uncapped cells of European Foulbrood gradually change color:

PennStateExtension+OLC-1006+2017+type@asset+block/S7efb-stages.jpg" alt="Color change from white to yellow to brown to nearly black of European Foulbrood larvae inside uncapped cells." style="box-sizing: border-box; border: 0px; vertical-align: middle; max-width: 100%; line-height: 1.4em; height: auto;">

Treatment

Preferred treatment options for EFB include simply waiting until a strong nectar flow begins allowing the bees to more effectively fight the disease. Requeening, particularly with a disease-resistance queen, can give the colony a more prolific queen and produce a break in the brood cycle, allowing house bees to remove diseased larvae from their cells. This bacterial disease can also be treated with specific antibiotics registered for use in honey bee colonies.

Sacbrood

How It Spreads

Sacbrood is a minor viral disease, affecting a small number of larvae at a time. It rarely causes severe losses. Sacbrood kills larvae in their cells, usually distributed among healthy brood.

Symptoms

Affected larvae change color from white to yellow or gray, and eventually to black. The thing to look for to identify sacbrood is a blackened, raised head in the cell. If a sacbrood-infected larva is removed from its cell, it will come out in one piece and look much like a fluid-filled sack.

Diagnosis

Larvae infected with Sacbrood die in cells with darkened and raised heads:

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They are easily removed, and the dead larvae resemble sacs of fluid:

PennStateExtension+OLC-1006+2017+type@asset+block/S7Sacbrood.jpg" alt="Sacbrood close up." style="box-sizing: border-box; border: 0px; vertical-align: middle; max-width: 100%; line-height: 1.4em; height: auto;">

Treatment

Sacbrood usually disappears when the nectar flow has started. There is no treatment for this disease other than keeping the colony strong and regularly requeening with disease-resistant stock. No antibiotic has shown effectiveness in controlling or preventing sacbrood.

Chalkbrood

How It Spreads

Chalkbrood is a brood disease caused by the spore-forming fungus Ascophaera apis. All castes of bees can be affected. This disease begins when spores are ingested in the larval food. They germinate in the hind gut of the larva then break through the gut wall, at which point the mycelial filaments consume the larval tissues and overcome the entire larva, encircling it in white, fluffy fungus.

Chalkbrood usually disappears when the temperatures rise and relative humidity inside the hive is reduced. It does not usually destroy a colony, but spores can remain viable for years, especially in brood combs. It can be easily transferred from hive to hive by robbing bees or by beekeepers moving combs, pollen and honey.

Spores can remain viable for years and can be transferred easily from hive to hive by robbing bees or by beekeepers.

Symptoms

This is the one disease that can be reliably identified from outside of the hive. As bees remove the dead larvae, which look like small pieces of white chalk, they can be seen at the hive entrance or on the ground around the hive.

Diagnosis

Chalkbrood-infected larvae in their cells:

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Dead-brood "mummies":

PennStateExtension+OLC-1006+2017+type@asset+block/S7chalkbrood_out.jpg" alt="Five small gray and white pods" style="box-sizing: border-box; border: 0px; vertical-align: middle; max-width: 100%; line-height: 1.4em; height: auto;">

Chalkbrood is easily diagnosed outside the hive:

 

PennStateExtension+OLC-1006+2017+type@asset+block/S7chalkbrood_at_entrance.jpg" alt="Dead bees laying all over the ground outside a hive entrance." style="box-sizing: border-box; border: 0px; vertical-align: middle; max-width: 100%; line-height: 1.4em; height: auto;">

Treatment

There is no definitive treatment for chalkbrood, but requeening with hygienic stock may be beneficial.