Pollinator

2007 Concise Encyclopedia. Related subjects: Evolution and reproduction

A pollinator is the biotic agent ( vector) that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain. Though the terms are sometimes confused, a pollinator is different from a pollenizer, which is a plant that is a source of pollen for the pollination process.

Types of pollinators

The most recognized pollinators are the various species of bees, which are plainly adapted to pollination. Honeybees are fuzzy and carry an electrostatic charge. Both features help pollen grains adhere to their bodies. Bees often also have a pollen carrying structure such as the corbicula of honeybees and bumblebees (also known as the pollen basket), or the scopa of the lower abdomen of megachilid bees, made up of thick bristles. Honeybees gather nectar, a concentrated energy source, and pollen, which is high protein food, to nurture their young, and inadvertently transfer some among the flowers as they are working. Honeybees need a steady source of pollen to multiply.

Euglossine bees pollinate orchids, but collect scents rather than nectar or pollen.

Lepidoptera ( butterflies and moths) also pollinate. They are not major pollinators of our food crops, but are important for many wildflowers.

Many other insects accomplish pollination. Wasps, bombyliid flies and syrphid flies are important pollinators of some plants. Beetles, and even thrips or ants can sometimes pollinate flowers. Green bottle or carrion flies are important for some flowers, usually ones that exude a fetid odour.

Bats are important pollinators of some tropical flowers. Birds, particularly hummingbirds, honeyeaters and sunbirds also accomplish much pollination, especially of deep-throated flowers. Other vertebrates, such as monkeys, lemurs, possums, rodents and lizards have been recorded pollinating some plants.

Plants fall into pollination syndromes that reflect the type of pollinator being attracted. These are characteristics such as: the size, the depth of the corolla, the colour (including patterns called nectar guides that are visible only in ultraviolet light), the scent, amount of nectar, composition of nectar, etc. For example, birds visit red flowers with long narrow tubes and lots of nectar, but are not as strongly attracted to wide flowers with little nectar and copious pollen, which are more attractive to beetles. When these characteristics are experimentally modified (altering colour, size, orientation), pollinator visitation may decline,.

Humans can be pollinators, as many gardeners have discovered that they must hand pollinate garden vegetables, because of pollinator decline. This can involve using a small brush or cotton swab to move pollen, or to simply tap or shake tomato blossoms to release the pollen for the self pollinating flowers. Tomato blossoms are self fertile, but have the pollen inside the anther, and the flower requires shaking to release the pollen through pores. This can be done by wind, by humans, or by a sonicating bee (one that vibrates its wing muscles while perched on the flower), such as a bumblebee. Sonicating bees are extremely efficient pollinators of tomatoes, and colonies of bumblebees are quickly replacing humans as the primary pollinators for greenhouse tomatoes.

Many kinds of pollinators, from blue bottle flies, to bumblebees, and leaf cutter bees are cultured and sold for managed pollination. Millions of hives of honeybees are also contracted out as pollinators by beekeepers.

Gallery

Scopa (pollen holder) of a Megachild bee

Halictid bee, showing adhering pollen

Syrphid fly, showing some adhering pollen