Most of the world’s calories are provided by a handful of wind-pollinated grasses, such as wheat, rice and maize. Nevertheless, most of the world’s crops need pollinators, chiefly bees, and it’s those pollinator-dependent crops that provide most of both the variety and the essential micronutrients in our diet. Without them, life would be unpleasant and very dull.
So reports that pollinators are having a hard time is bad news. But how bad exactly? At one extreme, it’s possible that even if pollinator numbers have declined, there are still enough left to provide our crops with all the pollination they need. Alternatively, the yield of most crops, in most places, might be limited by inadequate pollination.
To distinguish between these scenarios, you need to make some observations. Specifically, for lots of separate crop fields, you want to know how many pollinators are visiting the flowers of the crop, and then you want to know the yield (of apples, pumpkins or whatever) of each of those fields. Put those sets of data together and you can see if pollination and yield are related.
If they’re not, then you don’t know what’s limiting crop yield, but you know it’s not pollination. But if there’s a nice positive relationship between pollinators and crop yield, then you know that most of your fields didn’t have enough pollinators. Actually, it’s worse than that – even your best fields might have done better with more pollinators.
That’s a lot of work, but a big group of American researchers have done it, and their results are published in the journal Proceedings of the Royal Society. Sparing you the details, some crops are strongly pollinator-limited, and some aren’t.
The yield of cherries and blueberries is commonly limited by inadequate pollination, and apples are always pollinator-limited. On the other hand, pumpkins and watermelons are not. But whether yield is limited by pollination or not, pollinators are valuable, indeed essential, for all those crops, and many others. The annual value of pollinator-dependent crops in the USA is over $50 billion (£37 billion).
What about the relative value of honeybees and wild pollinators, chiefly bumblebees and solitary bees? Again this varies with the crop, but wild bees are generally more important than honeybees.
The massive Californian almond industry is the exception that proves the rule. To make sure they are adequately pollinated, the one million acres of Californian almonds (which produce 80 per cent of the world’s almonds) need fully two-thirds of the 2.7 million honeybee colonies in the entire USA. Nearly all those bees, about 30 billion of them, have to be trucked across America from other states.
It’s a mind-bogglingly huge, complex, expensive operation. For most other crops, wild bees do most of the job for nothing, so you can see why it pays to look after them.
Anyway, so much for America. In Britain, agriculture and other kinds of land use are both smaller in scale, and more mixed up, and gardens and allotments in towns and villages are pollinator hotspots. So by looking after your local pollinators, you’re also doing your bit to help everyone, amateur or professional, grow more and better apples, strawberries, blackcurrants, courgettes, beans or whatever.
Ken Thompson is a plant biologist with a keen interest in the science of gardening. His most recent book is Notes From a Sceptical Gardener, the second collection of his Telegraph columns. Visit books.telegraph.co.uk.