Where have all the bees gone?

By Aileen Marshall

bee

Photo: Böhringer Friedrich

Perhaps you’ve heard in the news about the mystery of the disappearing bees. It seems no one knows exactly why, but we do know that it’s serious. While bees may be an annoyance that can mar your outdoor activities, they are very important for pollinating crops. Some estimates say the drop in the bee population has cost as much as $200 billion in increased costs of produce, according to a United Nations study in 2005. The USDA has found an average cost per year to farmers to have bees pollinate their crops around $15 billion. One blueberry farmer claimed that his pollination cost used to be about $250,000 a year, now it’s about $750,000. Almonds are particularly dependent on bee pollination, and many nuts, berries, fruits and vegetables are also reliant on pollination. This increased cost gets passed on to the consumer in the form of higher prices.

There has been a growing business in beekeepers providing pollination services for farmers, since there has been a decrease in wild honey bees. These businesses are mostly migrant, moving with the seasons. Some have speculated that the constant moving has also put a stress on bees. This also makes it difficult to study this disorder.

The current phenomenon of disappearing bees is called colony collapse disorder (CCD). It is characterized by a hive where there are no live adult bees except for the queen and larvae, and there is plenty of food. With few dead bees found, it is difficult to find a definitive cause. It seems the bees don’t come back to their hives. Normally when a hive is abandoned, nearby bees will loot their food, but in CCD, the food remains untouched.

While there have been episodes of bees disappearing in the past, this one is notable in that there has been a sharp decrease of an average of 33% per year since 2006, primarily in the Americas. While it is normal to have attrition in colonies over the winter, CCD has been notable in the sharp decrease that occurs in the summer.

Only honey bees are affected by CCD. The type used by North American beekeepers is Apis mellifera. Not native to North America, it was brought over by European colonists. Ironically, the crops most dependent are those that were imported from Europe.

The honey bee consists of three castes: the queen, the worker and the drone. The queen is a female who is fed royal jelly instead of honey. She communicates to the workers and drones where the flowers are, and where to build the next hive. The queen has a sack called spermatheca that she uses to store sperm with which the eggs are fertilized.The workers are female; they feed the larvae, secrete beeswax from their glands to build the
comb cells, receive nectar and pollen from the drones and later join the drones to look for food. Drones are males from unfertilized eggs. They mate with the queen and go out to forage for food. Pollen and nectar are food for bees. They make honey from the nectar, which is used as food for the colony. Pollen is a protein source which can be used when there is not enough nectar or honey.

There have been many hypotheses proposed and studied as to what is causing CCD. While it is not definitely proven yet, the cause seems to be a combination of pathogens and insecticides. Bees can be infected by varroa mites. These bugs transmit viruses to the bees in the same way mosquitoes infect people with malaria. They can transmit deformed wing virus and acute paralysis virus. These varroa mites have been found in a significant number of studies of CCD. A miticide called coumaphos is most commonly found in CCD hives. Also, there is a fungus called Nosema that infects bee’s digestive tracts and has been found in some bees from abandoned colonies. Significant levels of fungicides were found in the wax of CCD hives in a 2013 study. Most evidence so far points to a class of insecticides called neonicotinoids. This class, consisting of imidacloprid, clothianidin, and thiamethonam, was first introduced because it showed a reduced toxicity to bees than earlier generation insecticides. While they do not cause mortality in the bees directly, there is evidence to suggest that low levels over long periods of time cause immunosuppression, making the bees susceptible to the fungus, mites and viruses found in CCD. Imidacloprid specifically can cause impaired communication, decreased foraging, flight activity and olfactory discrimination—all symptoms of CCD. While Europe has been working on reducing the use of neonicotinoids, in 2004 the Bush administration lifted a ban on pesticides that included neonicotinoids.

Many studies have been done on other possible causes, such as cell phones, cell towers and electromagnetic radiation. These studies failed to show any correlation. The USDA suggests the public plant more bee-attracting plants and limit the use of insecticides during midday, when bees are most active.

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