The unexplained rise in honeybee deaths – mainly due to high winter losses in honeybee colonies in the EU, and ‘Colony Collapse Disorder’ (CCD) in the USA – has become an issue of great concern. As honeybees are one of the most important pollinators for wild plants and crops, they are closely linked to both agriculture and biodiversity.

Since 1961, there has been a 45 percent rise in the managed honeybee population worldwide. Nonetheless, in recent years a number of beekeepers have experienced serious bee losses in Europe, the US and elsewhere.

In the USA adult bees have been disappearing from colonies since 2006; abandoning their queen, their brood, and their food reserves in what has been termed ‘Colony Collapse Disorder’ (CCD).

In contrast, a number of European beekeepers have witnessed unusually high bee colony losses during winter since the 1990s. Reliable surveys have estimated colony losses of 5 to 35 percent in the period 2002 to 2010, with a peak over the 2002/03 winter. Losses of around 10 percent would previously have been considered normal.

Separately, there have been occasional reports of bee poisoning, caused by the mismanagement of crop protection products.

A variety of interlinked factors are potentially to blame

There is a growing belief that interacting factors, including parasites, diseases, nutrition, beekeeping practices, weather patterns and genetics may be challenging the survival of bees.

Parasites and viruses can spread easily in today’s highly connected world. Both Varroa destructor (a parasitic mite and vector of viruses) and Nosema spp. (a parasitic fungus) weaken immunity and bee health. As a result, many viruses – previously known to cause no symptoms of ill-health in bees – have become fatal.

The limited genetic diversity of honeybees – bred from a limited number of lines to become less aggressive and more productive – may also affect immunity. For example, it is estimated that the entire honeybee population of the USA can be traced to 500 queens.

Modern farming has also reduced the variety of pollens within the agricultural landscape, impacting bee diet and also immunity. New stresses have been created by the bees’ changing environment as commercial pollination requires beekeepers to transport hives over long distances to foreign environments while confined in close proximity to each other.

Climate change can be considered as another factor, bringing harsher winters and wetter springs to Europe. Young bees that survive these conditions often have impaired health.