Mystery of the Vanishing Bees

HENFIELD, UK: A flurry of reports from the US and other parts of the world suggest that bee populations are under stress. Taking measures to prevent the loss of bees in the US or Europe may not be enough. For a sustainable agriculture, to prevent extinction of more local species, the world needs a “save the bee” policy.

The alarm is particularly intense in North America, where the term “Colony Collapse Disorder” has been coined. The condition is alleged to have wiped out one quarter of the 25 million honey bee colonies in the US. Declines in bee populations have occurred before, at various times and in various parts of the world. Yet this decline has caught the public imagination.

What’s new is the scale of the reported losses, and their economic importance in view of their occurrence in spring, shortly before the season for pollinating almonds, a high-value crop entirely dependent on bee pollination.

While most of the major world staple food crops such as wheat, maize and rice are in fact wind-pollinated, the majority of the foodstuffs that make eating interesting and enjoyable, such as fruits and nuts, require insects for pollination – the transfer of pollen from the male to the female parts of a flower – to set fruit or seed. Many other crops that we grow as vegetables, eating the leaves, shoots or roots, also require insect pollination to set seed in the first place, as do many of the forage legumes, such as clovers, which are so valuable in animal production.

Even more important, but virtually impossible to quantify in economic terms, is the role of bees in the pollination of wild plants. We know little about the pollination requirements of many wild plants, including some of the rarest and most threatened.

There are actually about 25,000 species of bees worldwide, but only a handful of those are managed commercially. By far the most important is the western honey bee, Apis mellifera, native to Eurasia and Africa, but now found worldwide. It’s this honey bee that suffers the well-publicized losses.

The causes of Colony Collapse Disorder remain unclear, with many theories suggested, including insecticides, genetically modified crops and mobile phones. More likely the disorder is caused by a combination of factors, especially disease and the stresses of modern commercial beekeeping, where colonies are transported thousands of miles on vehicles. For example, the same colonies may be moved from pollinating oranges in Florida, to apples in Pennsylvania, to blueberries in Maine and then back to Massachusetts for cranberry pollination.

A particular suspect is inadequate control of the parasitic mite Varroa destructor, which has caused enormous economic loss worldwide over the last 30 years. To reproduce, the mite sucks the blood of both adult bees and pupae and, in doing so, transmits various bee viruses, normally innocuous, but which can lead to the rapid and spectacular death of colonies. Beekeepers in many developed countries successfully prevented the mite for a long time by using convenient plastic chemical strips.

Unfortunately, the mite has become resistant to the most widely used chemical, and in parts of the US, some mites are now resistant to two different chemicals simultaneously, leaving few available options for mite control. The alternatives are mostly less effective and time consuming, hence unsuitable for commercial beekeeping. As well as harming managed colonies, the mite has almost eliminated feral honey bee colonies, once common and providing a background pollination service.

Unfortunately, honey bees are not the only species about which we should be concerned. Less publicized research from many parts of the world, including the recent comprehensive European Union–funded ALARM Project, based at the University of Leeds, conclusively demonstrates that populations of other bee species in Britain and the Netherlands have declined in both numbers and distribution over the last 50 years, with many local species extinctions occurring.

Again, reasons for these declines are complex, but changes in land use and the intensification of agriculture appear to be the main causes. Different species of bee nest in a variety of places, ranging from hollow trees to holes in the ground, and suitable sites for nesting have become scarcer as a result of intensive agriculture and increased urbanization. An example of this is the obsessive desire by many local authorities to destroy any tree showing any evidence of rot, for safety reasons, which has greatly reduced the choice of sites available to cavity-nesting bees. Obsessive tidiness involving the frequent cutting of grass and the removal of uncultivated areas also reduces suitable homes for ground-nesting bee species.

As food, all bees require both nectar for energy and pollen for protein, both provided by flowers. The widespread use of herbicides reduces the availability of flowering weeds in both arable crops and in grassland. Removal of hedgerows and other areas of semi-natural vegetation reduces the availability of flowering herbs, shrubs and trees. Some widely grown crops such as oilseed rape (canola), sunflowers and beans may provide short-lived bursts of food and can provide honey surpluses, but may also be sprayed with insecticides. Well-documented losses of bees caused directly by spraying have occurred in many countries over the years, although developed countries have reduced the problems, with less harmful chemicals and improved application techniques.

Despite this, monocultures of crops cannot supply the continuity of food supply throughout the season, essential for bees to successfully complete their life cycles.

Clearly, scientific research has a major role in reversing the decline in bees. The precise causes of Colony Collapse Disorder need to be established as a matter of urgency, but in the longer term, our understanding of many diseases of honey bees remains imperfect, and our understanding of the diseases of other bees is largely nonexistent.

Our understanding of relationships between wildflowers and bees is also poor, yet the implications of this lack of knowledge can be serious. One can, for example, envisage a situation where the only successful pollinator for a particular rare perennial wildflower species is a similarly rare bee species. If the bee disappears, the plant may carry on living for years, but without setting any seed, before anybody notices. If the rare bee has become extinct, it may then be too late to save the flower.

Although species extinctions are irreversible, land-use changes can to some extent be reversed. What is necessary is to set aside areas for wildlife, including bees, and provide food sources for them. Recent changes in agricultural support in Europe, through reform of the Common Agricultural Policy, potentially allow for the provision of many such measures, including the planting of mixtures of pollen- and nectar-rich mixtures around the edges of fields, as well as tree planting and the provision of hedges. Organic farming also promotes the reintroduction of legumes such as clovers into grassland.

Such measures to help bees inevitably have financial implications. Governments around the world must allocate resources, and not simply to support an ailing beekeeping industry. Bees not only make enormous contributions to national economies through the pollination of crops, but also have a vital role in supporting the biodiversity and viability of natural ecosystems. To provide suitable habitat and food for bees on a sufficient scale, many people worldwide must make small changes, which in turn requires considerable research, education and coordination on the part of governments.