Marcelo Aizen & Lawrence Harder, Straits Times 27 Mar 10;
IN THE past five years, as the phenomenon known as colony collapse disorder spread across the United States and Europe, causing the disappearance of whole colonies of domesticated honeybees, many people have come to fear that our food supply is in peril. The news on Wednesday that a US Department of Agriculture survey found American honeybees had died in great numbers this winter can only add to such fears.
The truth, fortunately, is not nearly so dire. But it is more complicated.
There is good news: While some areas are seeing a shortage of bees, globally the number of domesticated honeybee colonies is increasing. The bad news is that this increase can't keep up with our growing appetite for luxury foods that depend heavily on bee pollination. The domesticated honeybee isn't the only pollinator that agriculture relies on - wild bees also play a significant role, and we seem intent on destroying their habitats.
To understand the problem, we need to understand the extent of the honeybee's role in agriculture. Humans certainly benefit from the way bees - and to a lesser extent, other pollinators like flies, beetles and butterflies - help plants produce fruits and seeds. Agriculture, however, is not as dependent on pollinators as one might think. It's true that some crops like raspberries, cashews, cranberries and mangoes cannot reproduce without pollinators. But crops like sugar cane and potatoes, grown for their stems or tubers, can be propagated without pollination. And the crops that provide our staple carbohydrates - wheat, rice and corn - are either wind-pollinated or self-pollinated. These don't need bees at all.
Overall, about one-third of our worldwide agricultural production depends to some extent on bee pollination, but less than 10 per cent of the 100 most productive crop species depend entirely on it. If pollinators were to vanish, it would reduce total food production by only about 6 per cent.
This wouldn't mean the end of human existence, but if we want to continue eating foods like apples and avocados, we need to understand that bees and other pollinators can't keep up with the current growth in production of these foods.
The reason is that fruit and seed crops that are most dependent on pollinators yield relatively little food per acre, and therefore take up an inordinate, and increasing, amount of land. The fraction of agriculture dependent on pollination has increased by 300 per cent in half a century.
The paradox is that our demand for these foods endangers the wild bees that help make their cultivation possible. The expansion of farmland destroys wild bees' nesting sites and also wipes out the wildflowers that the bees depend on when food crops aren't in blossom. Researchers in Britain and the Netherlands have found that the diversity of wild bee species in most regions in those countries has declined since 1980. This decrease was mostly due to the loss of bees that require very particular habitats - bees that couldn't adapt after losing their homes and food sources to cultivation. Similarly, between 1940 and 1960, as land increasingly came under cultivation in the American Midwest, several bumblebee species disappeared from the area. It is difficult to count and keep track of wild bee populations globally, but their numbers are probably declining overall as a result of such human activity.
Even if the number of wild pollinators remained stable, it would not be sufficient to meet the increasing demand for agricultural pollination. Could domesticated bees take up the slack? By looking at data from the Food and Agriculture Organisation of the United Nations, we found that the number of managed honeybee hives increased by 45 per cent during the past five decades.
Unfortunately, this increase cannot counteract the growing demand for pollination or the shortage of wild pollinators. Domesticated bees mainly produce honey; any contribution they make to crop pollination is usually a secondary benefit. In most parts of the world, they provide pollination only locally and not necessarily where it is needed most.
Thus a vicious circle: Fewer pollinating bees reduce yield per acre - and lower yield requires cultivation of more land to produce the same amount of food.
Eventually, a growing shortage of pollinators will limit what foods farmers can produce. If we want to continue to enjoy almonds, apples and avocados, we have to cultivate fewer of them, more sustainably, and protect the wild bees that help make their production possible.
Marcelo Aizen is a researcher at the National Scientific and Technical Research Council of Argentina. Lawrence Harder is a professor of pollination ecology at the University of Calgary.
