CCD (Colony Collapse Disorder) is referred to as ‘a disease with unknown cause’. There have been numerous unsuccessful attempts to make links between the pathogens present and the circumstances and/or symptoms. In fact, in the research, scientists have got no further than describing the CCD phenomenon. CCD is considered to have occurred when the following symptoms are present:
- almost no bees in the hive, and no dead bees either
- bees disappear suddenly, bees disappear from the hives quickly
- there is a great deal of brood present
- there are a number of young bees + a queen bee present
- there is sufficient food
When defining CCD, people have limited themselves to the symptoms. But it is just as important to look at where and when CCD occurs.
CCD usually occurs later in the year (from August onwards), as well as in the winter period. CCD is common in almost the entire USA as well as Europe. Depending on the location, 10 to 25% of bee keepers are confronted with CCD. Where CCD does and does not occur in Europe has not been precisely documented, the monitoring reports do not provide these details.
It is unclear to what extent is the presence of dead bees in the vicinity of the hives is also part of the CCD phenomenon.
Further analysis of CCD
First of all it is important to establish that in CCD there is a change in behavior of the whole colony.
The presence of only a few nurse bees indicates that these have become foragers in a short space of time.
The urge of bees to leave suddenly is attributable to the change in the composition of the food.
If the bees are found in the vicinity of the hives, this may be due to a disturbance in the flying function. This is attributable to lack of energy or inability to fly any distance (including misshapen wings due to deformed wing virus (DWV).
The normal ratio of bees and brood in a honey bee colony is, in a rough general sense, 2 adult Honey Bees to 1 cell of sealed brood.
When the ratio reverses to 1 adult honey bee to 2 - 3 cells of sealed brood...this is the latest definition of CCD.
Characteristics in common with winter mortality
There is something wrong with the foragers in both winter mortality and CCD. In CCD, nurse bees suddenly become foragers. In winter mortality, due to the lack of brood there are only foragers.
All too often bee colonies are reported dead in the autumn or winter while the food supply is sufficient. It is unclear as to whether bee colonies do not survive the winter due to ‘hunger’ or because they cannot maintain the temperature in the hive. In principle, bees can cope quite well with low temperatures. A low temperature in the hive may be due to insufficient energy for the flight muscles, because too much energy is needed to maintain the immune system.
The commonly reported starvation (heads in the combs) may be due to the fact that the winter cluster is not moved.
Abandoned hives are not scavenged. Apparently the food is not appealing. This leads to the suspicion that there is something wrong with the food, for example:
- Something is missing from the food
- The food has become contaminated with a microorganism (for example by yeasts or fungi)
- The bees are not attracted to the smell of the food.
We think that the cause of winter mortality is also the cause of CCD. The CCD phenomenon can be fully explained by a change in the composition of the food, which results in a change in the microbial composition. At high temperatures this can easily happen in one day. At lower temperatures, this takes 2 - 3 days.