Skip main navigation

£199.99 £139.99 for one year of Unlimited learning. Offer ends on 28 February 2023 at 23:59 (UTC). T&Cs apply

Find out more

Pollination Biology

Dr Juliet Osborne discusses the mechanics behind how insects pollinate the plants which produce our food.
I’m Juliet Osbourne I’m a professor in applied ecology and I’m a pollination biologist and pollination is the way in which flowering plants reproduce where pollen is moved between the male parts of the flower and the female parts and fertilization happens and then that grows into seed and fruit. Insects are really good at pollination, the flowers have evolved so they have a lot of adaptations which attract insects to those plants, such as their color their scent, the nectar they produce which is a really good food source for insects.
So the insects are attracted to the plants and the flowers and then they will feed on those flowers but at the same time they pick up pollen on their bodies which can then be transferred to other flowers, so it’s a very efficient means of that pollen being moved around.
There’s lots of different insect groups which pollinate flowers mostly the bees, the butterflies and moths, hoverflies even beetles can pollinate plants but in terms of crop pollination bees are probably some of the most important and those are wild bees we call them solitary bees or bumble bees and the social bees and of course honey bees which often live in hives or boxes that are managed by beekeepers or humans and bees are really efficient pollinators because they are collecting the nectar for themselves but also the pollen to take back to their brood in the colonies which makes them really efficient at pollination and many many of our crops depend on them.
The reason that I’m talking to you about pollinators is because a third of our global food production depends on pollinators and that is 87 crop species that depend on insect pollinators and that’s a lot of our fruit crops, our seed crops and our nut crops. There is a sort of urban myth that humans wouldn’t survive if bees died out because of the pollination of crops and it is really important but actually our basic diet of wheat and corn and rice, the sort of staple crops in our diet depend on wind for pollination actually so they don’t need insects but the for the nutritious diets that we now expect for a healthy lifestyle and for all the vitamins that we need we need all those fruits that and vegetables that are pollinated by insects.
So which crops are particularly dependent on insects? Well I’m Standing here in a courgette field some people call it zucchini it’s a member of the pumpkin squash family and that family of plants are particularly dependent on insect pollinators to produce the large fruits with lots of seeds that you know includes pumpkins, squashes, melons cucumbers and courgettes as you can see here. This courgette field is in Cornwall which is in the southwest of England and it is pollinated by bees that are local to the area bumblebees and honeybees primarily.
Other crops that we grow that need insect pollinators include the fruit crops such as strawberries and raspberries the tree fruits like apples and pears, almond crops and other nut crops and actually you might not realize but even coffee and chocolate depend on insect pollination. So chocolate depends on the growing of cocoa crops and cocoas are actually pollinated not by bees, not by butterflies, but by tiny little midges so who knew that actually midges are really important otherwise we wouldn’t have chocolate.
Production of insect pollinated crops has increased by about 300% over the last 50 years because of managing agricultural managing more land and managing it more intensively and that is because we have need more food for a growing population but actually the paradox of that is our intensive management of those farms and those crops means that it is causing a threat to the pollinators themselves which we depend on for that food production so this isn’t really sustainable.
So we have pretty good evidence now that there have been regional and national and probably global declines of some of our pollinating species and part of this is because there is less habitat for them to survive in so the more land that we farm the less areas are left for them to survive in and feed on when the crops are not in flower and also how we manage the land where the crops are is going to affect those pollinators.
They can get food from the crops these courgette fields provide a lot of nectar for the bees which is great but if crops are sprayed with insecticides or if herbicides are used to remove weeds from the field this can all affect the pollinators and their survival in the landscape.
We know more about the pollinator populations in Europe and in North America because we’ve been able to monitor them over longer periods over several decades although we’re still quite data deficient but actually in Latin America in Africa and Asia we know very little about those populations and the biodiversity so we actually know very little about the risks that are currently encountered by those crops and the crop growing and how stable that crop production is. How can we ensure sustainable and flourishing pollinator populations?
Well we have to think about how we manage the land that we’re farming for those beneficial insects as well as for the crops that we’re producing and that might mean putting aside different areas of land into habitats where those pollinators and other beneficial insects can thrive or it might be about how we manage the crop itself.
In terms of how we manage the land that we put aside there are what we call agri-environments schemes in Europe and also in the US which for example include growing wild flowers in the margins and we know that the insect pollinators will respond to these, if we’re producing more food for those pollinators in the margins it will mean more bees available to pollinate the crops in the fields and that can be quite a successful technique in terms of how we manage the field itself we need to think about which chemicals we’re using on the crops and if we can find more selective or benign chemistry that manages the damaging insects so we can keep controlling the pests if you like but ensuring that we don’t have effects on the pollinating insects.
So another way to increase crop pollination is to actually introduce pollinators into the crops so that’s particularly important where you have crops growing in polytunnels or glass houses for example and I’m here in a polytunnel that is growing strawberry plants to grow strawberry fruit and so they introduce here at Travaskis farm they introduce bumble bee colonies to pollinate those crops and you can see up here they place a bumble bee colony in a container just at the top of the polytunnel and those bees will forage for nectar and pollen on the crop and they will pollinate the plants while they were doing that to produce these beautiful strawberries that you can see here.
A lot of pollinators are also introduced where beekeepers will introduce honey bee hives for pollination of large scale crops such as almonds as well in the fields. But using pollinators in this way where you introduce manage pollinators obviously doesn’t affect the wild bee population it doesn’t increase the wild bee population and sometimes it can have negative effects. So when you introduce colonies of bees they may contain diseases or they may compete for floral resources or nectar and pollen and that might be bad for those wild pollinator populations so it has to be managed very carefully and we have to think about the decisions we’re making about pollination in that way

Dr Juliet Osborne discusses the mechanics behind how insects pollinate the plants which produce our food.

For the agricultural industry, insects can be pretty serious pests of crops: eating and damaging the plants and fruits, or spreading disease.

But there are a great variety of insects that are beneficial to crop production, such as ladybirds and spiders that act as natural enemies to help control the insect pests, or insects such as bees and butterflies which play a crucial role in pollinating those crops.

In fact, we depend on insect pollination for the production of many seeds, fruits and nuts which contribute to a varied and nutritious diet across the globe.

What is pollination?

Pollination is a critical step in the sexual reproduction of flowering plants. It is defined as the transfer of pollen (the male gametes) from the anthers of one flower, to the stigma of another flower. The pollen grain then grows a tube, down through the style, to reach the ovary of the flower. Here, the male gamete fertilises an ovule, producing an embryo which grows into a seed or nut.

This growing seed is often protected by the development of a soft nutritious fruit. For this process to work, pollen needs to be moved between flowers to ensure what is termed ‘cross-pollination’, and this means that something needs to transport the pollen. In some crops, such as wheat and maize, the pollen is transported by the wind.

In the majority of crops however, the pollen is transported by insects. Often these are insects specifically adapted to visit flowers to feed on their nectar (a sugary food source produced by the flower) or pollen. In doing this, the insect picks up pollen from one flower and then, on visiting another flower of the same species, deposits this pollen and effects fertilisation.

So, without pollinators where would we be? The Food and Agriculture Organisation (FAO) recognise this threat and have developed a Global Action Plan on Pollinators. Further information and the report they have compiled including a list of crops benefiting from insect pollination can be found via the link at the bottom of the page.

Which insects?

Over 300,000 insect species visit flowers for food rewards (such as nectar and pollen) or shelter, and so are potential pollinators. Pollinators come from many different types of insect families, particularly the Hymenoptera (ants, bees and wasps), Lepidoptera (butterflies and moths), Diptera (flies and midges) and the Coleoptera (beetles). The best known, and probably the most effective pollinators overall, are bees.

There are nearly 20,000 species across the globe, and the groups that are most well-known for pollination of crops are the honeybees, the bumblebees and a variety of solitary bee species, such a squash bees and leafcutter bees. These insects are so effective at pollination because they visit flowers to collect nectar and pollen to feed to their brood, and often exhibit ‘flower constancy’ which means they focus on visiting one species of plant during a foraging trip. When they do this, it is much more likely that pollen transported on their bodies will reach the stigma of a flower of the same species, so there is more chance that pollination will be successful.

A bumblebee (Bombus terrestris L.) pollinating a borage flower (Borago officinalis L.) Figure 2.6.1. A bumblebee (Bombus terrestris L.) pollinating a borage flower (Borago officinalis L.) Photo by bigemrg

Threats to crop pollination

Successful crop pollination depends on abundant and diverse communities of insect pollinators available when a crop is flowering. We have seen declines in some pollinator populations over the last 20 years, due to habitat loss (particularly floral resources), prevalence of diseases and parasites, and also as a result of management of crops – such as the use of some insecticides and herbicides that remove flowering weed resources. This is a complex set of problems and different pollinators are affected differently. However, at the same time, there has been a global increase of around 300% in the production of crops that depend on insects so it is likely that the global pollination deficit is set to increase as we continue to manage land intensively. This of course goes hand in hand with the increases in global demand for food as our population grows..

A honeybee pollinating a yellow flower A honeybee (Apis mellifera L.) pollinating an oilseed rape flower (Brassica napus).

How can we manage pollination?

The best way to boost wild pollinator numbers is to ensure that floral resources are provided in the agricultural landscape throughout the season, and ensure the pollinators have nesting and over-wintering sites.

Having uncropped habitats and less intensively managed land will improve the populations and ensure resilient pollination services over the long term.

But, since crops flower intensively over large areas for short periods, growers often introduce managed colonies of bees (honeybees, bumblebees or solitary bees) to their fields to boost pollination and crop yields.

This is a temporary solution to a deficit in pollinators but can be an effective way of securing yields in crops grown over large areas such as almonds, apples, oilseed rape (canola) or alfalfa.

The downside to this approach is the potential of introducing novel diseases into the resident population of pollinators.

This article is from the free online

Grand Challenges: Food for Thought

Created by
FutureLearn - Learning For Life

Our purpose is to transform access to education.

We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.

We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.

Learn more about how FutureLearn is transforming access to education