Bijensterfte, oorzaken en gevolgen

When we think about bees, the first thing that springs to mind is usually the honey bee or bumble bee. Yet these two actually represent a small fraction of bees in North America. There are a staggering 4,000 species of native bees, from tiny metallic green sweat bees, short-lived squash bees, amazing clay-sculpting mason bees, leaf-cutting bees with outsize heads and large jaws, to large, blue-black carpenter bees. Now they, too, are showing signs of decline, but the threats facing them are entirely manmade. The overuse of pesticides has had an obvious, detrimental impact, but others are more insidious. Many pollinators are generalists, meaning they can feed from a wide variety of plants. When their habitats are destroyed, for example, to make way for a commercial or housing development, they at least have a chance of finding new foraging in a flower garden. The problem for native bees is that many of them specialize in particular native plants, and once those are eliminated, they starve. Habitat destruction can also mean that nesting sites suddenly become inhospitable.

Some of these bees collect leaves as nest material, while others harvest tiny hairs from plant leaves like lamb's ears. Some nest in premade cavities like holes drilled in wood, while others dig nests in the ground.

The differences between these fascinating creatures are numerous, but native bees and their enormous contributions as pollinators are often unfairly eclipsed by their better known relatives. To produce seeds and reproduce, three-quarters of the world's flowering plant species rely on animal pollinators, like bees, bats and some birds.

It has been widely reported that honeybeepopulations across the globe have experienced catastrophic decline, owing to both the condition called Colony Collapse Disorder and from infection by tracheal mites. Much has been made of the potential threat to commercial fruit and nut production, and it is a justifiable concern. Yet our native bees, those pollinator heavyweights, labor in obscurity, pollinating blueberries, cranberries, peppers, tomatoes, alfalfa and squash. It has been estimated that they perform $3 billion worth of pollination services a year. Now they, too, are showing signs of decline, but the threats facing them are entirely manmade.

The overuse of pesticides has had an obvious, detrimental impact, but others are more insidious. Many pollinators are generalists, meaning they can feed from a wide variety of plants. When their habitats are destroyed, for example, to make way for a commercial or housing development, they at least have a chance of finding new foraging in a flower garden.

The problem for native bees is that many of them specialize in particular native plants, and once those are eliminated, they starve. Habitat destruction can also mean that nesting sites suddenly become inhospitable.

A case in point, the current trend towards mulching flowerbeds with a couple of inches of bark makes it impossible for ground-nesting bees, like digger bees, to excavate their tunnels. These small drab bees go largely unnoticed, but they are one of the most abundant wild pollinators.

There's reason for concern

To understand why we should be concerned about the fate of an insect, we need to be aware that one out of every three mouthfuls of food we eat is delivered to us by pollinators. Many creatures within an ecosystem also rely on pollinators for the same reasons. Many North American birds feed on the fruits, seeds and berries of plants pollinated by native bees.

The insects themselves, and their larvae, provide protein for adult songbirds and their fledglings. Other animals like raccoons, skunks and possums eat the fruits, nuts, bulbs and roots of animal-pollinated plants.

Losing a pollinator can mean a whole ecosystem is in danger of unraveling. The good news is that the damage can be undone. The North American Pollinator Protection Campaign, NAPPC, a diverse group of ecologists, conservationists and horticulturalists, was formed in 1999 to encourage activities that protect the numbers and health of resident and migratory pollinating animals.

One of the ways the NAPPC suggests that we help protect native bees is to create a bee-friendly garden at home or within our communities. This means planting oases of eye-catching native plants like purple coneflower, rudbeckia and ratibida, hyssop, coreopsis, larkspur, Joe-pye weed, blanket flower, sunflower, lupine, evening primrose, poppy, penstemon, salvia and sedum.

Annual and biennial flowers like milkweed, cosmos, poppy, mullein and daisies will also draw native bees, as will wild roses and blueberry bushes, raspberry and blackberry brambles, elderberry and sumac.

The composition of a garden is an important factor. Plants that are placed in large groups of the same kind will attract the most bees. By braving your neighbors' displeasure and opting for a less manicured wild garden, you will create a more hospitable home for them.

As robust weeds, like Queen Anne's lace and white clover, often flower from early spring to hard frost, they can be invaluable forage for bees building up strength over winter. By leaving small areas mulch-free and unmowed, you enable solitary native bees to make their nests without disturbance.

Your endeavors on their behalf will be well rewarded. Native bees come in a wide range of colors and shapes and in the course of a day you could be visited by metallic blue bees, yellow and black striped bees, black bees with white polka dots, and white and black striped bees. Some are tiny enough to creep down the most fragile flower tubes, while others have huge wings that shower pollen on surrounding plants.

Put simply, there is a touch of the marvelous about them.

Bron:
Nashoba Publishing, Harvard News, September 11, 2009
http://www.nashobapublishing.com/harvard_news/ci_13314984