Who are the Pollinators?

A. Native Pollinators. Pollinators comprise a significant portion of the total diversity of species on this planet. In fact, between 200,000 – 300,000 invertebrate species—such as butterflies, beetles, moths, flies, and bees—are estimated to serve globally as pollinators.^{22 23} A good estimate for vertebrates species is around 2,000, including birds, mammals, and reptiles.²⁴ A few examples of pollinators around the world include:^{25 26 27}

Native pollinators maintain the health of ecosystems and habitats on which many other creatures rely. They also are important, but often overlooked, crop pollinators. Native bees, butterflies, moths, and flies are at least equally and in many cases even more adept than honey bees at pollinating the 100–150 major U.S. crops requiring pollinators.²⁸ Recent research conducted in California’s Central Valley has demonstrated that when adequate habitat remains, native bees can meet the needs of even those crops with a heavy pollination demand such as watermelon. This pollination is not provided by a single species of bee but by a suite of over 30 species that give year-on-year security despite natural population fluctuations.²⁹

On a global scale, at least twenty genera of animals other than honey bees provide pollination services to many of the world’s 100 most important crops. Collectively, these species pollinate at least as many crop species as do managed honey bee colonies.³⁰ For example:

• In the U.S., wild-living native bees pollinate many crops that are ineffectively pollinated by honey bees including blueberries, cranberries, eggplants, kiwi fruits, and tomatoes.^{31 32}
  • On oceanic islands, bats pollinate many economically important plants such as wild bananas, agave, durians, and several species of eucalyptus and palms³³ , as well as most of the rainforest canopy trees.Biting midges are the primary pollinators of cocoa.³⁴
  • Most of the world’s 750 fig species rely on wasps for pollination. Figs are a critical resource for both people and animals living in many tropical forest communities. In some areas, figs may constitute as much as seventy percent of the diet of vertebrate species.³⁵

B. Managed Bees. Honey bees (Apis mellifera) are often the first things that come to mind when someone mentions pollinators. This common association is a likely consequence of the honey bee’s prevalence in agriculture, and its regular appearances on nature programs, even in children’s books. Honey bees are not native to North America; they were brought here by European settlers in the seventeenth century to provide honey and wax, two important products much valued by households of the time.³⁶ The honey bee’s ability to adapt to new environments means that feral (naturalized) colonies can be found pollinating flowers and scouring for food in most backyards, gardens, and wild areas throughout the continent. The rise in importance of managed honey bees as crop pollinators occurred during the twentieth century for two reasons, 1) improvements in the hive and its management that occurred in the nineteenth century³⁷, and 2) the decline in native bees due to habitat loss and pesticide use.³⁸ Pollination is now big business: since 1992, over one million honey bee colonies have been rented from commercial beekeepers yearly for pollination of agricultural crops in the U.S..³⁹

There has been recent concern among the agricultural industry as researchers have accumulated evidence showing that honey bee colonies are seriously threatened in the U.S.. Managed and wild colonies declined by twenty-five percent during the 1990s and by over fifty percent since the 1940s. Available data show that in 1947 there were 5.9 million managed colonies in the U.S.; in 2005, there were 2.4 million.^{40 41} Information is less clear for feral honey bees, although it is believed that their numbers may have fallen by 75 percent or more in the last thirty years.⁴²

Many factors are believed to be responsible for what is being called “Colony Collapse Disorder”.  Four broad categories of potential causes currently being studied are: pathogens; parasites; environmental stresses, which include pesticides and extreme weather conditions; and management stresses, including nutrition problems, mainly from nectar or pollen scarcity.⁴³ Many experts suggest that these declines illustrate the danger of our heavy reliance on a single species for most of our pollination needs.

An increasing number of other bees are being managed for crop pollination in North America. This is partly in response to the troubles facing honey bees and partly because honey bees are not the most efficient pollinator for all crops. The blue orchard bee (Osmia lignaria), for example, is widely used to pollinate apple and cherry orchards. Pollination of an acre of apples may require as few as 250 of these solitary-nesting bees, a job that would require up to 2.5 honey bee hives (c. 50,000 bees).⁴⁴ Other bees are important pollinators of particular crops. The alfalfa leafcutter bee (Megachile rotundata) and the alkali bee (Nomia melanderi) pollinate alfalfa in western North America. Bumble bees (genus Bombus) are used in glasshouses for tomatoes and other Solanaceae crops that were previously hand pollinated. Of course, these managed bees are not without their own problems. The movement of captive reared bumble bee colonies appears to have spread the Nosema pathogen to native Bombus occidentalis in the western U.S. leading to a steep decline range wide ^{45 46} and the possible extinction of two other species (NRC report ⁴¹).