that co-evolved with native plants and have adapted to col- lect and transfer pollen grains with each flower visit. For example, honey bees visit alfalfa to collect nectar, but


their bodies, which lack pollen-collection structures on the underside of the abdomen, fail to ‘trip’ the alfalfa flowers. As a consequence, the bees come away without pollen. Blueber- ries, cranberries, and tomatoes require buzz-pollination, in which the bee rapidly rotates its abdomen against the flowers’ pollen-loaded anthers, transferring pollen to its body in the process. Bumble bees (Bombus spp.) buzz-pollinate, making them ideal pollinators for such crops. In contrast, honey bees fail to pollinate these plants. Similarly, the flowers found on apple trees are not well pollinated by honey bees. These trees are better served by the hornfaced bee (Osmia cornifrons). As an additional drawback, honey bees often make long- distance foraging trips, visiting flowers well outside the crop field or orchard they are intended to pollinate. Perhaps the biggest issue concerning the use of honey


bees to pollinate crops is colony collapse disorder (CCD), which was first documented with a decline of 30 to 90 per- cent of honey bee colonies in the winter of 2006-2007. CCD is characterized by a sudden loss of foragers and other adult bees from the colony, a low adult-to-brood ratio, and a lack of dead bees in the vicinity of the hive.1


The Need for Native Pollinators


In light of the extensive losses of managed honey bee colonies, recognition of, and efforts to encourage populations of, native pollinators are increasingly important. Globally, over 16,000 species of bee have been described — of which only seven are honey bees. Unlike honey bees, many of the remaining species are specialists, which co-evolved with native plant species and are best able to pollinate those plants. They have also evolved to emerge from their nests at the time of year when their host plants are in bloom. As a result, native bees are an essential component of plant-pollinator food webs throughout the world. In addition, the sheer numbers of native pollinators


boost pollination efforts when the availability of honey bees declines. Researchers have found that native bees account for over 50% of crop pollination in the United States, despite belief by farmers that their crops are entirely pollinated by managed honey bee colonies. Native bees are particularly abundant on small agricultural fields with nearby trees and a variety of flowering weedy species. Such findings underscore the importance of habitat


in promoting biodiversity. Loss of habitat is considered a major contributing factor to loss of native bee diversity in Europe. Suitable habitat may not be completely lost; how- ever, researchers have found that ‘partial’ habitat loss—loss of either food resources or nesting sites—is sufficient to lead to a decline in the number of pollinators. All parts of the complete habitat must be present for individuals to complete their life cycles and perpetuate the species.


Alison Pearce Stevens, Ph.D. is a zoologist and ecolo- gist who spent her undergraduate career studying honey bee behavior. She recently moved from Berlin, Germany to Lincoln, Nebraska, where she writes animal and ecology- based articles for children.


VISIT www.greenteacher.com/contents93 for a list of common crop species and their animal pollinators (scroll down to the links for this article’s supplements). Also online, you will find tables showing the nesting habits, timing and distribution of native bees, and common bee genera (scroll down to the links for this article’s supplements); the following 5 activities for ages 9 and up: Pollination Exploration, Nest Search, Building a Nesting Block, Behavioral Observations and Busy Bees.


References


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Bosch, J. and Kemp, William P., “Alfalfa Leafcutting Bee Population Dynam- ics, Flower Availability, and Pollination Rates in Two Oregon Alfalfa Fields,” Journal of Economic Entomology 98(4) (2005), pp. 1077-1086.


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Cane, J.H. and Tepedino, V.J., “Causes and extent of declines among native North American invertebrate pollinators: detection, evidence, and conse- quences,” Conservation Ecology 5(1): 1 (2001), <http://www.ecologyandsociety. org/vol5/iss1/art1>.


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Kearns, C., Inouye, D. and Waser, N., “Endangered Mutualisms: the conservation of plant-pollinator interactions,” Annual Review of Ecology and Systematics 29 (1998), pp.83-112.


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Packer, L., Genaro, J.A., and Sheffield, C.S., “The Bee Genera of Eastern Canada,” Canadian Journal of Arthropod Identification No. 3, 25 September 2007, <http://www.biology.ualberta.ca/bsc/ejournal/pgs03/pgs_03.html>.


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Winfree, R. et. al., “Wild bee pollinators provide the majority of crop visitation across land-use gradients in New Jersey and Pennsylvania,” USA Journal of Applied Ecology 45 (2008), pp. 793-802.


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Notes


1. Although researchers are still investigating the causes of CCD, bees in hives affected by the disorder have been shown to be infected with a higher number of pests and pathogens (tracheal mites, Varroa mites, hive beetles, and viruses). In addition, apiaries with at least one CCD-affected hive are more likely to have multiple CCD-affected hives, which suggests an element of transfer from one colony to another.


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