<P> Hand pollination, also known as mechanical pollination is a technique that can be used to pollinate plants when natural or open pollination is either undesirable or insufficient . This method of pollination is done by manually transferring pollen from the stamen of one plant to the pistil of another . This is often done with a cotton swab or small brush, but can also be done by removing the petals from a male flower and brushing it against the stigmas of female flowers, but can also be done by simply shaking flowers in the case of bisexual flowers, such as tomatoes . Common reasons for choosing this method include the lack of pollinators, keeping control of cross-pollination between varieties grown together, and creating specific hybrids . Examples of this are vanilla plants, which are transported to areas where its natural pollinator doesn't exist, or plants grown in greenhouses, urban areas, or with a cover to control pests, where natural pollinators cannot reach them . Pollinator decline and the concentrated pollination needs of monoculture can also be a factor . However, these are not the only reasons, and variable techniques for hand - pollination have arisen for many specialty crops . For instance, hand - pollination is used with date palms to avoid wasting space and energy growing sufficient male plants for adequate natural pollination . Because of the level of labor involved, hand - pollination is only an option on a small scale, used chiefly by small market gardeners and owners of individual plants . On large - scale operations, such as field crops, orchards, or commercial seed production, honeybees or other pollinators are a more efficient approach to pollination management . Despite this, hand - pollination is a fairly widespread practice . Pears grown in Hanyuan County, China have been hand - pollinated since the 1980s, because they can't be pollinated with other varieties that have different flowering times; also, lice infestation requires the use of many insecticide sprays, which causes local beekeepers to refuse to lend beehives . </P>

What part of the system does a hand pollinator replace