Thursday, December 17, 2015

What do insects have to do with eating, drinking and kissing this Christmas?

We don’t often associate insects with Christmas. However, without them, we wouldn’t have many of our Christmas foods, drinks and decorations. This is because many of the plants that produce our Christmas treats rely on insects pollinating flowers earlier in the year. Without these insects, we wouldn’t have bright red holly berries to decorate our Christmas puddings, mistletoe with its characteristic white berries to kiss under, cranberries to liven up our turkey, chocolate, marzipan or many of the spices and other goodies we associate with Christmas. This is because insects are needed by most plants for cross-pollination, which results in the production of fruits and seeds. Since plants cannot move to find mates themselves, they rely on insects to bring male and female together.

Holly (Ilex aquifolium) is unusual in the plant world because male and female flowers occur on separate shrubs. As bees drink nectar from male flowers, they get pollen on their bodies and when they move to a female plant to continue to feed, they deposit that pollen on female flowers. The pollen causes the female flowers to be fertilized, and to form fruits (or berries) containing the fertilized seeds.

A bumblebee visits a Holly flower in Co. Wicklow in
April to drink nectar. (Photo J. Stout)

Similarly, mistletoe (Viscum album) also holds its male and female flowers on separate plants. Plants are partially parasitic and live on the branches of other trees but still rely on insects (not just bees, but also flies, bugs and beetles) for pollination and thus berry production. In fact, both mistletoe and holly fetch higher prices at market if they have berries on them, and so insect pollinators are of economic value at Christmas time as well.

Cranberry bushes (Vaccinium macrocarpon) produce both the male and female structures not just on the same plant, but in the same flower. However, they still need bees to transfer the pollen between flowers, because those male and female structures do not mature at the same time.  Large bees, such as bumblebees, which can shake the flowers at just the right frequency to dislodge the pollen (producing a distinctive buzzing sound) are the best pollinators. This is known as “buzz pollination” and is important in other crops too (including tomatoes and blueberries).

Chocolate-producing cocoa trees (Theobroma cacao) produce small flowers on their trunks, and although flowers don’t produce a scent to attract pollinators, they produce a small amount of nectar and are visited and pollinated by tiny flies (midges). Although flowers contain both male and female structures, they cannot fertilize themselves, and these midges are needed for the production of cocoa fruits, which contain the seeds from which we derive chocolate. These trees grow in the tropics and flowers and fruits are produced throughout the year, although it takes 5-6 months for them to mature before they are harvested.

Marzipan (almond paste) is made of ground almonds (and sugar). Almond (Prunus dulcis) trees bloom in early spring and are visited by bees – both managed honeybees and wild bees. In fact, almond trees in California (where most of the world’s almonds are produced) produce better yields when both honeybees and wild bees are present in orchards. This is because they complement each other in their foraging. If there are no bees at all visiting flowers, fruit set can plummet by up to 90%.

Honeybees are important pollinators of
almond flowers (Photos J. Stout)

Many of our Christmas spices, including cinnamon (Cinnamomum spp.), cloves (Syzygium aromaticum) and nutmeg (Myristica fragrans), essential ingredients in Christmas cakes, puddings and mulled wine, also need pollinating by insects. In the case of cinnamon and cloves, this is done by bees, but for nutmeg, it’s beetles that do the pollinating job.

So, as you enjoy Christmas this year, raise a glass to the insects that made all of this possible.

For more information on pollinators, their value and conservation, see the All Ireland Pollinator Plan www.biodiversityireland.ie/pollinator-plan

Posted: Professor Jane Stout

Originally published in the Independent supplement on the Science of Christmas 14th December, 2015

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