Wikipedia
Hand pollination (also called "mechanical pollination") is a technique used when natural, or open pollination is insufficient or undesirable. The most common techniques are for crops such as cucurbits, which may exhibit poor pollination by fruit abortion, fruit deformity or poor maturation. Hand-pollination is an option only on a small scale, but is a common technique by home and small market gardeners, involving the transfer of pollen with an artist's brush or cotton swab from male to female flowers. Sometimes the corolla is removed from male flowers and the flower itself is brushed against the stigmas of female flowers.
The principal reasons for hand pollination include a paucity of natural pollinators, avoiding cross-pollination between varieties grown together or, conversely, in the controlled production of hybrids.
Hand-pollination can be the simple act of shaking, with tomatoes and other self-fertile flowers. In general, tomatoes grown in greenhouses need aid in pollination, which has been done by hand or with an electric vibrator for a long time. Recently, it has been mostly supplanted by cultured bumblebees.
When pollination is needed on a large scale, such as for field crops, orchards, or commercial seed production, honeybees or other pollinators are cultured and provided for pollination management.
The primary reason for hand-pollination is lack of pollinators, which may be due to the act of moving crops from home areas (as in vanilla beans) without also taking the natural pollinator. Pollinator decline or the concentrated pollination needs of monoculture may also be other factors in pollination shortage. When growing plants in urban environments lack of pollinators is often an issue as well.
Another reason for hand-pollination is in order to control the parents of the seed to be produced. For example, all F1 hybrids are the result of pollinating one specific variety with another specific variety, in order to produce a uniform crop.
For pest prevention with some high-value crops, row covers of mesh are used to prevent pest insects from access to the plants. However, this may necessitate hand-pollination when bloom starts.
Hand-pollination is used with date palms to avoid wasting a lot of space and energy growing sufficient male plants for adequate natural pollination.
Variable techniques for hand-pollination have arisen for many specialty crops.
Pears grown in Hanyuan County, China have been hand-pollinated since the 1980s in order to produce better fruit. The Jinhuali pear was promoted by China authorities but farmers quickly discovered that it can't be pollinated with other varieties that have different flowering times. They tried hand pollination and it worked well. In the same pear, lice infestation requires the use of many insecticide sprays; in this condition, local beekeepers refuse to lend beehives. If humans were to replace bees as pollinators worldwide, the annual cost would be estimated to be $90,000,000,000.[citation needed]