Honeybees (Apis mellifera), the predominant pollinators of economically important plants and crops, have been facing sharp population declines around the world since the 1980s. Recently, the die-off of honeybees has been dramatic, with beekeepers in the United States losing more than 42% of their colonies between April 2014 and April 2015, after a 5-year period in which the annual bee losses averaged more than 30%. This troublesome statistic is made even more alarming by the fact that the number of bee deaths in summer exceeded those in winter. Because summer is the most productive and vigorous time for bees, any disruption of their health during the summer season is severely detrimental. Studies have linked the deaths of the pollinators to numerous and varied stressors, including viral pathogens, parasitic pests (such as Varroa mites), habitat loss, climate change, inadequate nutrition, compromised immune systems (possibly as the result of colony collapse disorder), and exposure to pesticides and insecticides (in particular, neonicotinoids). However, no individual stressor has yet been singled out in the scientific consensus as a primary culprit, so it is likely that a combination of these stressors, and possibly others, is to blame. See also: Beekeeping; Colony collapse disorder; Herbicide; Honeybee genome; Hymenoptera; Immunosuppression; Insect diseases; Insecticide; Pathology; Pesticide; Pollen; Pollination; Social insects; Virus

Honeybee (Apis mellifera). (Photo by Peggy Greb, Agricultural Research Service, U.S. Department of Agriculture)

Honeybees provide more than 80% of the agricultural pollination services dispensed by insects. About 90 different agricultural plants and crops rely on honeybee-mediated pollination for their maximum production, so any significant reduction in the colony numbers of these bees will have a tremendously adverse effect on the producers of fruits, vegetables, nuts, and flowers. Thus, investigators have sought to determine the exact cause (or causes) of these drastic declines in bee numbers. The economic and ecological repercussions from these bee losses are so serious that, in May 2015, the executive branch of the U.S. government proposed a National Strategy to Promote the Health of Honey Bees and Other Pollinators. This strategy seeks to provide remedies to restore and sustain the health of the honeybee populations in the United States. The die-offs of bees are occurring throughout the world, however. Many countries in Europe, Asia, and South America (in particular, France, Germany, Spain, Belgium, the Netherlands, and Japan) have reported bee losses equaling or exceeding those observed in the United States. See also: Agricultural science (animal); Agricultural science (plant); Agriculture; Entomology, economic; Population ecology