Honey bee health: Key diseases explained

American foulbrood is caused by the spore forming bacteria Paenibacillus larvae. Infected larval brood usually die at the pre-pupal or pupal stage, after the cell has been capped.

The decomposed larvae create a scale like formation on the cell that is difficult to remove.

This scale is full of spores that transmit the disease, and the bees are unable to remove it. The queen will not lay in these cells.​

AFB spores can remain viable for over 50 years and are very resistant to freezing and high temperatures.

Often an outbreak can be traced to the re-use of old equipment which was infected. This is why thorough cleaning and disinfection is vital when using second-hand equipment. ​

There is no treatment for AFB. If it is confirmed, bees, frames, honey and any other related items must be destroyed in accordance with instructions from the Scottish Government Honey Bee Health Inspectors. If instructed, boxes must be scorched or bleached according to guidelines found in the useful information section.

Symptoms:

• Sunken, greasy cappings.
• Roping.
• Scale.
• Perforations often at the side of cell after cell is capped.

Additional information about American foulbrood can be found on our Education page.

European foulbrood or EFB is caused by Melissococcus plutonius bacteria.

Larvae become infected after ingesting food contaminated with the bacteria and will begin to show symptoms before the cells are capped.

The bacteria then multiply in the mid-gut of the larvae and compete for larval food, resulting in the larvae dying of starvation.

Strong colonies may have the bacteria present but live with it in small quantities – the bees can remove infected larvae.

The incidence of EFB is generally higher when the colony is under stress, which may be caused by hive movement, beekeeper manipulations, climatic conditions such as cool and wet weather conditions, or poor nutrition.

Heavy infestations will affect a large percentage of the brood, weakening the colony over time, and possibly leading to the death of the colony.

Symptoms:

• Healthy larvae are pearly white and segmented.
• The larvae look melted in the cell, twisted, discolored and with no segmentation.

Additional information about European foulbrood can be found on our Education page. 

Brood diseases affect the developing larvae and pupae of honeybees.

Chilled brood can occur if there is a drop in the adult population and there are not enough bees in the hive to generate and maintain the optimal temperature of 34.5°C needed to keep the brood sufficiently warm. The brood at the edges of the brood nest become neglected. Those that survive may become more susceptible to chalkbrood.

Although the condition is called ‘chilled’ brood, it is not necessarily caused by chilly weather, but by a reduction in the adult population, perhaps by disease or colony splitting. It can be triggered by looking into a hive too early in the season when the temperature is low.

It can look quite worrying as the brood turns grey/black.

You can find more information in the booklet "Foulbrood disease of honeybees and other common brood disorders" downloadable from our Education page.

Brood diseases affect the developing larvae and pupae of honeybees.

Chalkbrood is a fungal disease caused by Ascosphaera apis.​

It is common in Scotland in the spring when temperatures are cooler.

When larvae ingest the fungus, it penetrates the gut wall, absorbs nutrients as it multiplies and causes the larvae to die of starvation.

The dead larvae look chalky, white and black.

The chalkbrood mummies (the remains of the decomposed larvae) can be seen on the hive floor. These are removed from the cells by the bees.

It does not cause too much harm unless the hive is heavily infected.

You can manage the infection with good biosecurity methods, re-queening, replacing combs and good ventilation.

You can find out more in the PowerPoint "Non-notifiable pests and diseases" in our Education page. 

Brood diseases affect the developing larvae and pupae of honeybees.

Sacbrood is a viral infection of the brood. ​Larvae that have become infected with Sacbrood Virus fail to pupate and die just after capping. It is a common disease during the first half of the brood-rearing season but because it only affects a small percentage of the brood, it does not usually cause colony loss.

You can reduce infection by re-queening the colony.

Regular comb changes such as a bailey comb exchange can help.

Good biosecurity can prevent the spread.

You can find out more in the PowerPoint "Non-notifiable pests and diseases" on our Education page. 

Brood diseases affect the developing larvae and pupae of honeybees.

Bald brood occurs when honey bee pupae are not capped and continue development exposed on the frame within the colony.

It is sometimes found in the presence of the honey bee pests, wax moths (Achroia grisella and Galleria mellonella), when their larvae tunnel under the brood cappings on the comb.

It can also occur when frames are positioned too close to each other within a colony. When frames are moved by the beekeepers, the bees will uncap brood to make room for movement between the frames, also causing bald brood.

More information coming soon. In the meantime, you can find useful information about chronic bee paralysis virus in our education pages. 

More information coming soon. In the meantime, you can find useful information about Nosema in our education pages.