Many valuable crops benefit from insect pollination; the transfer of pollen from the male parts of a flower to the female part of a flower. Cross-pollination is the transfer of pollen among different plants or varieties of the same species. This process increases fruit yield and, often, the size of the fruit. Honey bees are important pollinators because they can be managed and easily moved to crop sites. In the United States, the added value to agriculture from honey bee pollination is over $14 billion annually, and many beekeepers earn extra income from renting colonies for pollination. In Georgia, bee hives are rented to pollinate apples, blueberries, cucumbers and watermelons. Professional recommendations vary for the number of hives needed for good pollination, but for these crops 1-2 colonies per acre is commonly used. If the pollen is compatible, fertilization of the ovule and seed formation occur. Generally, more seeds develop when large numbers of pollen grains are transferred. Seeds, in turn, stimulate surrounding ovary tissue to develop so that, for example, an apple with many seeds will be larger than one with fewer seeds. In this way, good pollination improves both fruit yield and size.
Many insects visit flowers to collect pollen and nectar as food. As they forage, these insects spread pollen grains among flowers, accomplishing pollination. Many flowers offer sugary liquid nectar as an added enticement for these pollinating insects. Among insect pollinators, bees are especially efficient because they eat pollen and nectar exclusively, visit many flowers of the same species during a single trip, and have hairy bodies which easily pick up pollen grains.
There are over 3000 species of bees in North America. Most of these are solitary bees, but a well-known minority are social, that is, they live together in colonies and cooperate in colony tasks. Both solitary and social species are important in crop pollination, but the social species - namely honey bees and bumble bees - are more easily managed.
Compared to honey bees, some wild bees pollinate certain crops more efficiently because of unique and desirable behaviors. For example, Southeastern blueberry bees buzz-pollinate blossoms by shaking pollen from the flower with high frequency muscle vibrations; for blueberry, this greatly improves pollination efficiency.
In many parts of the country, fruit and vegetable growers are concerned about declining numbers of wild bees. Human activities destroy bee habitat and forage. Generally, growers are receiving less "free" pollination from wild bees and increasingly they must make up for this by renting managed honey bee hives during bloom periods.