Pollination is the movement of male pollen to the female part of the flower (stigma), the first step in successful seed and fruit production by the plant. Self-pollination is when pollen is transferred from the anther to the stigma within a single plant. Cross-pollination is the transfer of pollen from one plant to the stigma of another plant. Once the plant has been pollinated, the male contribution fuses with the egg in the ovary, the process known as fertilization. After fertilization, the fruit and seeds develop and mature.
Although the male parts and female parts generally reside in a single flower, plants often have elaborate mechanisms to prevent self-fertilization. In some species the stigma of the flower ripens first, before the anthers are shedding pollen. As a result, it may be fertilized only by pollen brought from an older flower. In other plants, the opposite is true. The pollen is mature and shed before the stigma ripens. Other plants, like squashes or watermelons, have sepa rate male and female flowers. A few plants, like mulberry or olive, have separate male plants and female plants.
Some plants, for instance grasses, produce light pollen grains that might be carried by the wind or water from plant to plant. Other plants need help from insects, birds, or bats for successful pollination. Without this assistance, fruit and/or seeds would not be formed. Indeed, about a third of the food Americans eat is the direct result of pollination by in sects.
More than 100 agricultural crops in the United States are pollinated by bees. This means bees are important, if not essential, for the production of almost $7 billion worth of agricultural crops produced annually in Arizona. Examples of bee pollinated crops include watermelons, cantaloupe, citrus and apples (see story below). Although some of these crops are pollinated by bee species other than honey bees, honey bees are the only ones that can be easily managed, moved around and are known to exploit a broad variety of crops.
While a worker bee is in a flower collecting nectar, pollen from the anther often sticks to her hairy body. Because the bee usually visits a number of the same type of flower in a patch, she’ll rub some of the pollen off onto the stigma of another flower and complete pollina tion. Some flowers like orchids have elaborate mechanisms to be sure bees are dusted with pollen when they visit.
Part of the reason honey bees are so important as pollinators is that they actively seek out flowers with pollen, unlike pollinators such as bats and hummingbirds who are primarily interested in nectar. Pollen stored in the hive is used as a source of protein in feeding the developing larvae.