Bees, both commercially managed honey bees and wild unmanaged bees, among many other types of insect pollinators, play an important role in global food production. In the United States, the value of pollination by bees and other insects to U.S. agricultural production is estimated at $16 billion annually. Most of this estimated value (about 75%) is attributable to honey bees. Given the importance of bees and other types of pollinators to food production, many have expressed concern about whether a "pollinator crisis" has been occurring in recent decades. Worldwide reports indicate that populations of both managed honey bees and native bees have been declining, with colony losses in some cases described as severe or unusual. In Europe, managed honey bee colony numbers have been declining since the mid-1960s, and individual beekeepers have reported "unusual weakening and mortality in colonies," particularly during the period spanning winter through spring. According to the United Nations, many insect pollinator species may be becoming rarer, causing some to question whether this is a sign of an overall global biodiversity decline. In the United States, honey bee colony losses due to bee pests, parasites, pathogens, and disease are not uncommon. This situation gained increased attention in 2006 as some commercial beekeepers began reporting sharp declines in their honey bee colonies. Because of the severity and unusual circumstances of these colony declines, scientists named this phenomenon colony collapse disorder (CCD). This issue was legislatively active in the 110 th Congress and resulted in increased funding for pollinator research, among other types of farm program support to protect pollinators, as part of the 2008 farm bill ( P.L. 110-246 ). Years later, the U.S. Department of Agriculture (USDA) reports that U.S. beekeepers continue to lose honey bee colonies each year. Since 2006, USDA estimates that overwinter colony losses have averaged more than 30% annually. However, USDA reports that bee colonies have continued to decline each winter for reasons not solely attributable to CCD, which is characterized by colony populations that are suddenly lost but no dead bees are present. (For more information on CCD, see text box on next page. Additional discussion is provided in " Factors Affecting Bee Health .") USDA claims that "beekeepers did not report CCD as a major cause of colony loss" for overwinter losses in most recent surveys. To date, the precise reasons for honey bee colony losses are still unknown. Reasons cited for honey bee population losses include a wide range of possible factors. Potential identified causes include bee pests and disease, diet and nutrition, genetics, habitat loss and other environmental stressors, agricultural pesticides, and beekeeping management issues, as well as the possibility that bees are being negatively affected by cumulative, multiple exposures and/or the interactive effects of several of these factors. Aside from the range of potential identified causes for bee colony declines, CRS Report R42855, Bee Health: The Role of Pesticides , addresses what role, if any, pesticides play in influencing the health and wellness of bees. Given continued concerns about the health and well-being of honey bees and other pollinators, this issue has continued to be legislatively active in Congress. Various proposals addressing managed bees and native pollinators were enacted in the 2008 farm bill ( P.L. 110-246 ) and reauthorized and expanded as part of the 2014 farm bill ( P.L. 113-79 ), in the law's research, conservation, specialty crop, and miscellaneous title provisions. More than 200,000 species of insects (bees, butterflies, moths, flies, wasps, beetles, and ants), bats (and other small mammals), and birds (including hummingbirds) are plant pollinators. This report focuses on bees—both managed honey bees and wild (mostly unmanaged) bee species. Honey bees ( Apis mellifera ; Family: Apidae) are the most well-known bee species. However, honey bees are only one of the world's estimated 17,000 described bee species, and one of the estimated total of 20,000 to 30,000 bee species worldwide. Honey bees are not native to North America, but were introduced by European settlers in the 1600s. Honey bees are considered to be "social" bees in that they have single egg-laying queen and sterile worker bees that tend to work together in a highly structured social order, consisting of cooperation and division of labor within a colony, as well as the presence of two generations in a single nest at the same time. Social behavior allows bees to be domesticated and managed. There are an estimated 115,000-125,000 beekeepers in the United States. Most of these (roughly 90,000-100,000) are hobbyists with fewer than 25 hives. Commercial beekeepers tend to have more than 300 hives. They migrate their colonies during the year to provide pollination services to farmers. In the United States, most pollination services are provided by commercial beekeepers. Some other types of native bees are also managed, such as bumble bees, orchard bees, and alfalfa leaf-cutting bees. Some of these bees (such as bumble bees and some types of stingless bees) exhibit some of the social behaviors commonly associated with honey bees. Some bumble bee species are managed in controlled environments to pollinate greenhouse tomatoes. Others are valued as primary or supplementary pollinators for members of the squash family such as cucumbers, watermelons, and cantaloupes. Some species of meliponine bees (commonly called stingless bees), which are mostly found in the tropics, were widely cultivated by Native Americans in Central and South America before the introduction of honey bees from Europe. Roughly 500 species of bees native to North America show some degree of social behavior. An estimated 4,000 species of bees are native to North America. With few exceptions, most of these are wild and not managed. Most types of wild bees are "solitary" bees—estimated at about 3,500 species—and do not have long-lived colonies. Data and information on native bees are more limited than information on managed bees. The five most common families of native bees in North America are Andrenidae, Apidae, Colletidae, Halictidae, and Megachilidae. Andrenid bees are all ground nesters, and mostly comprise a large family of dark, nondescript bees, although some are colorful. Bees in the large Apidae family include not only honey bees, but also bumble bees (such as Bombus spp. ), carpenter bees, squash or gourd bees, and others. Compared to most native species, bumble bees ( Bombus) are better studied. There are 239 species of bumble bees worldwide; of these, 60 species are found in the United States, Mexico, and Canada. Bees in the smaller Colletidae family are broader and wasp-like, and include plasterer bees. Bees in the Halictidae family include many species of sweat bees, and most have shiny metallic colored or black bodies. Bees in the Megachilidae family include resin and mason bees, orchard bees, and leaf-cutter bees that mostly nest in holes. Most families of bees contain some types of parasitic and cuckoo bees. For a summary of the different types of wild bees see the text box above. Worldwide, the contribution of bees and other insects to worldwide crop production for human food is valued at about $190 billion each year. In the United States alone, the value of insect pollination to U.S. agricultural production is estimated at $16 billion annually, of which about three-fourths of the value is attributable to honey bees. Expressed somewhat differently, another widely cited estimate is that bee pollination of agricultural crops is said to account for about one-third of the U.S. diet, contributing to the production of a diverse range of high-value fruits, vegetables, tree nuts, forage crops, some field crops, and other specialty crops. Both managed and wild bees are critical to plant pollination and are economically valuable to U.S. agricultural production. Bee pollination of agricultural crops is said to contribute to the production of as many as 90 agricultural crops. A number of agricultural crops are almost totally (90%-100%) dependent on animal pollination, including apples, avocados, blueberries, cranberries, cherries, kiwi fruit, macadamia nuts, asparagus, broccoli, carrots, cauliflower, celery, cucumbers, onions, legume seeds, pumpkins, squash, and sunflowers. Other specialty crops also rely on pollination, but to a lesser degree. USDA reports that native bees also provide pollination services for a number of food crops. In addition to some of the aforementioned crops, these include alfalfa seeds, almonds, canola, chokecherries, grapefruit, pears, plums, prunes, soybeans (hybrid seed production), tomatoes, vegetable seeds, and watermelons. The role of bee pollination in enhancing agricultural productivity and crop yields for many types of fruit, vegetable, tree nut, and field crops was also noted in a series of published studies as part of the United Nations' Global Pollination Project. Native bees are thought to be more efficient at pollination than honey bees and are known to pollinate native plants, such as cherries, blueberries, and cranberries, as well as other commercial crops including almonds, among other fruiting and flowering plants. The economic value of pollination services provided by managed honey bees and wild bees is difficult to quantify. Most available estimates focus on crop pollination by managed honey bees. Data and information on native bees are more limited.