Bees really don't intend to pollinate flowers, although pollination benefits them because it creates seeds that will make more flowers that will provide them with a continuing nectar flow in the future. Pollen transfer is passive; unless the bee is deliberately collecting pollen to take to the nest, the pollen a bee carries from one flower to another has been deposited by the plant on her back or in another place where she was unable to remove it when she instinctively groomed herself to eliminate dust and debris. As bees go from flower to flower collecting nectar, some of the collected pollen is inadvertently deposited on the stigma of a flower of the same species, resulting in cross-pollination.
At certain times when there is a large amount of brood in the colony, honey bees' primary goal is to actively collect pollen for larval food, storing the pollen on their hind legs on dense hairs referred to as a pollen basket. These hairs surround a groove, on the external hind tibia, that creates an elongated cup-like surface where the pollen sits. Bees are able to move some of the passively collected pollen into the pollen baskets, and once the pollen is packed into the transport structures, it is no longer available for pollination and is carried back to the nest.
Lawrence Harder and James Thomson describe flowers that have a dispensing schedule, requiring bees to visit more frequently because the flower's structure allows only a limited amount of pollen to be obtained in each visit. This increases the likelihood of passive transfer of at least some pollen instead of larger amounts being actively removed to provide larval food or lost to in-flight grooming.
More than one hundred crop species in the United States rely to some degree on bee pollination, and these crops constitute approximately one-third of the American diet, including the majority of high-value crops like fruits, vegetables, and nuts. Specifically, honey bees' pollination activities are important for almonds, apples, blackberries, blueberries, melons, cherries, peaches, pears, nectarines, cucumbers, cranberries, and soybeans. Honey bees pollinate the bulk of these crops, which are worth more than fifteen billion dollars to the U.S. economy, and they also contribute indirectly to the production of meat, milk, and cheese because they pollinate food crops used for livestock.
Bumble bees pollinate 10 to 15 percent of all the crops grown in the United States, particularly crops raised in greenhouses, including tomatoes, peppers, and strawberries. Fruits and seeds produced by insect pollination are important in the diet of about 25 percent of all birds and mammals, and bees also pollinate crops that provide shelter for birds and wild animals, and they pollinate plants that prevent erosion of the soil and keep creeks clean for aquatic life in wildlife habitats.
In Sichuan Province in China, pesticides have totally eliminated the bee population in an area that was famous for its production of pears. Rather than lose the crop, farmers in that area hand pollinate the pears. They collect pollen from the male parts of the flowers, dry it, and then climb into the pear trees and dust pollen on each flower with a feather, enabling fertilization and the production of the prized fruit.
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