The well-known social insect, the honey bee (Apis mellifera), is helpful to horticulturists. The female worker collects pollen and nectar in special pockets (honey baskets) on its hind legs. This is a supply of food for the hive and, in collecting it, the bee transfers pollen from plant to plant. Several crops, such as apple and pear, do not set fruit when self-pollinated. The bee therefore provides a useful function to the fruit grower. In large areas of fruit production the number of resident hives may be insufficient to provide effective pollination, and in cool, damp or windy springs, the flying periods of the bees are reduced.
It may therefore be advantageous for the grower to introduce beehives into the orchards during blossom time, as an insurance against bad
weather. One hive is normally adequate to serve 0.25 ha of fruit. Blocks of four hives placed in the centre of a 1 ha area require foraging bees to travel a maximum distance of 70 m. In addition to honey bees, wild species, e.g. the potter flower bee (Anthophora retusa) and red-tailed bumble-bee (Bombus lapidarius), increase fruit set, but their numbers are not high enough to dispense with the honey bee hives.
All species of bee are killed by broad spectrum insecticides, e.g. deltamethrin, and it is important that spraying of such chemicals be restricted to early morning or evening during the blossom time period when hives have been introduced.
In commercial greenhouses, the pollination of crops such as tomatoes and peppers is commonly achieved by in-house nest-boxes of bumble-bees, Bombus terrestris (see Figure 10.5). Plant breeders may use blowflies in glasshouses to carry out pollination. They also perform mechanical transfer of pollen by means of small brushes.
When a pollen grain arrives at the stigma of the same plant species, it absorbs sugar and moisture from the stigma's surface and then germinates to produce a pollen tube. The pollen tube contains the 'male' nucleus (and also an extra 'second nucleus'). These nuclei are carried in the pollen tube as they grow down inside the style and into the ovary wall.
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