I have seen reports over a number of years now that the western honey bee (Apis mellifera) is dying off due to a phenomenon called colony collapse disorder (CCD). But recent work has shown that mysterious peaks of honey bee deaths have occurred over the ages ever since records began to be compiled. Investigations of CCD have failed so far to pin the cause down a single unique culprit. Many factors seem to be involved that cumulatively put bee hives under pressure. And the latest twist in the story is an editorial in Science claiming, not that the honey bee is dying out, but that current huge numbers of domesticated beehives can damage the environment.
Pollination is necessary for plants to reproduce and the honey bee is a pollinator. When feeding on flowers the bee transfers pollen grains that produce male gametes (sperm cells) from the flower stamens to the flower pistils that bear the female gametes (egg cells). The resulting fertilisation of eggs by sperm results in the formation of seeds. Honey bees are domesticated on a grand scale just like cattle, chickens and pigs, not for the honey they produce but because they are good pollinators. Pollination by domesticated honey bees is involved in the production of over 70 per cent of the world’s crops with an estimated annual worth of around $200 billion (€162 billion).
In CCD most worker bees in the colony disappear leaving the queen, some immature bees and plenty of food. This phenomenon has occurred often over the history of agriculture, eg in Ireland in 950, and was known by various names, eg disappearing disease. It was renamed CCD in 2006. Over 10 million beehives were lost from 2007 to 2013, frequently to CCD, but overall global beehive stock rose from about 50 million in 1961 to 83 million in 2014, an average annual growth of 1.3 per cent. Annual growth has increased to 1.9 per cent since 2009 (UN figures).
CCD seems to be caused by multiple factors. Bees have a hard life that makes large energy and cognitive demands. Bees must travel long distances to collect pollen and nectar and then must find their way back to the hive again. This requires physical endurance and sophisticated spatial awareness and memory. Anything that interferes with these capacities can reduce the bees’ ability to find food and to make it back home, and bees that don’t make it home die.
Bees are therefore particularly susceptible to “sub-lethal stressors” that don’t kill outright but that interfere with behaviour. Managed beehives are vulnerable to many pests, predators and viruses that have spread around the world by international trade. The worst pest is the Varroa destructor mite. Also, intensive agriculture can affect bees’ nutrition and damage their brains. Climate change can alter the relationship between bees and their food plants. Pesticides and diesel fumes can interfere with chemical communication in the brain and reduce foraging efficiency.
The evidence as to exactly what causes CCD is inconclusive to date. Environmental activist groups have concentrated on the role of neonicotinoid pesticides in CCD and the EU currently has a moratorium on the use of certain neonicotinoids. A 2009 study by Dennis vanEngelsdorp and others evaluated 61 different factors, including pesticides, and no single stressors stood out as the primary cause of CCD. However, CCD colonies had more pathogens than colonies without CCD. However, the most recent studies described by Sam Wong in New Scientist report that higher levels of neonicotinoids have a negative effect on reproduction in wild bees.
The recent Science editorial warns that our extensive use of honeybees as pollinators can damage the environment. The honey bee is just one of over 25,000 bee species and these other bees also make a valuable contribution to pollination. Pollination-industry beekeepers move beehives from pollination site to pollination site which means introducing huge numbers of a new species into each new area to compete with indigenous species for resources and to carry in new diseases to infect the indigenous species. The authors suggest much more attention must be paid to how beehives are deployed and that account must be taken of the effect on local pollinators.
William Reville is an emeritus professor of biochemistry at UCC