Among all pollinators (hummingbirds, bats, butterflies, flies and some beetle), bees are unique. In addition to sipping nectar to fuel their own flight, they are one of the few animals to actively gather large amounts of pollen (and hence inadvertently scatter some of it widely between flowers). Rich in protein, the pollen of many plant species serves as the principle food source for developing bee larvae.
More than one-third of the world’s crop species such as alfalfa seed, sunflower, and numerous fruits and vegetables depend on bee pollination, an ecological service valued in North America at $20 billion a year. In North America the trends in honey bee numbers are decidedly downward, with the number of managed hives decreasing by 50% since the 1950s and the amount of crop acreage requiring bee pollination at an all time high. The cereal grains that make up the largest part of our diets, such as corn, rice and wheat, are wind pollinated. Thus the prospect of human starvation in the absence of bees is remote, but crop declines in the most nutritious—and arguably, most interesting—parts of our diet like fruit, vegetables, and alfalfa for meat and dairy production, are possible.
While honey bees pollinate most of our crops, other bees are also important pollinators. The solitary blue orchard bee, Osmia lignaria, flies early in the spring when it might still be too cold for honey bees, pollinating fruit trees like apples and cherries. And the squash bee Peponapis pruinosa will seek out pumpkins, squash, and other cucurbits to the exclusion of all else, making it a superior pollinator for those plants. Bumble bees make great tomato and pepper pollinators thanks to their habit of buzzing the flower to shake pollen loose. Bees ensure garden plants, ornamentals, and wildflowers get adequate pollination. The world of bees is full of examples like this.
Source:University of Minnesota, http://www.beelab.umn.edu