Colony Collapse Disorder

Colony Collapse Disorder (CCD) is a specific picture in which the adult bees disappear from the hive within a short time without leaving dead bees behind; it was described in the USA in the winter of 2006–2007. Today it is accepted that most colony losses are not caused by a single mysterious disease but by mutually reinforcing factors, above all varroa and the viruses it carries. In a dwindling hive, the first job is to carry out a "post-mortem" to find the real cause.

The original definition

The term was used for colonies in which the following findings occurred together:

• A rapid decline in adult worker bees within a few weeks,
• No dead bees in the hive or in front of it,
• Capped brood, honey and pollen still in place,
• The queen and a small number of young bees remaining,
• Robber bees and pests such as wax moth arriving late at the emptied hive.

The distinguishing point is the absence of dead bees: the bees did not die in the hive but disappeared outside. Reports matching this narrow definition fell markedly after the first few years.

What do we know today?

Most researchers take the view that losses are due not to a single factor but to several factors acting together:

• Varroa and viruses: The biggest single cause of losses. The mite transmits viruses such as deformed wing virus (DWV) directly into the bee and shortens the life of winter bees.
• Nutrition: Scarce or one-sided pollen, drought, insufficient winter stores.
• Pesticides: Even sublethal doses can impair foragers' orientation and learning.
• Nosema and other agents: Nosema ceranae in particular has been linked to losses in some studies; on its own it is not an explanation.
• Queen and management: An old or poorly mated queen, late or ineffective varroa treatment.

Why are there no dead bees? Sick bees, or bees with a high virus load, leave the hive and die outside. That is why autumn dwindling caused by varroa also often gives the impression that "the bees have disappeared".

Post-mortem of a dwindling hive: step by step

1. Close the hive immediately. Close or reduce the entrance. Until the cause is found, do not give its combs or honey to another hive; a foulbrood may be involved.
2. Look in front of the hive and on the floorboard: Are there dead bees, how many, and how are they lying?
3. Stores: Is there honey and pollen in the comb? Are the dead bees head-first in the cells?
4. Brood: Are there perforated or sunken cappings, dead pupae, white chalky mite faeces on the upper walls of the cells?
5. Queen and eggs: Is there a queen, are there fresh eggs, are there several eggs per cell?
6. Other traces: Brown faecal stains on the frames, mould, signs of mice, torn-open honey cells.
7. Surroundings: Has there been spraying nearby, is there a similar picture in neighbouring hives?
8. Count mites in the other hives. The mite levels of the hives in the same apiary often provide the answer.

Likely cause by sign

Prevention

• Measure varroa all year round; treat in late summer before the winter bees are reared, and count again afterwards.
• Go into winter strong: sufficient honey and pollen stores and a young, well-laying queen.
• Support nutrition: supplementary feeding in drought and pollen dearth.
• Communicate with your surroundings: talk to nearby farmers and the local village or neighbourhood administration about spraying times.
• Keep records: mite counts, treatments and losses per hive are the best guide for the following year.

Misuse of the term

Calling every colony loss "Colony Collapse Disorder" is a common but harmful habit: it stops the search for the real cause. Giving this name to a colony that dwindled because of varroa leads to the same loss being repeated the following year. The term is valuable as a historical definition, not as an explanation. Most losses have an identifiable and preventable cause.