Bijensterfte, oorzaken en gevolgen

[Summery story by Dr. Henk Tennekes on the background for starting this Dutch website]

Bees are dying at an alarming rate. Mortality doubled in Holland over the last six years. Elsewhere in Europe and in the US the situation is similar. In parts of China farmers are even forced to pollinate by hand. This ecological crisis threatens to bring global agriculture to a standstill. What are the reasons behind the decline of bee colonies across the globe? Some scientists believe pests, such as the varroa mite or Nosema ceranae, are at the root of this devastation. Recent French studies, however, suggest that these pests struck particularly hard in areas where a new class of insecticides, the so-called neonicotinoids, were being used. Neonicotinoids are insecticides which act on the central nervous system of insects with lower toxicity to mammals. The insecticides are water soluble and thus readily translocated in plant tissue and particularly effective against sucking insects. The application rates for neonicotinoids are much lower than older, traditionally used insecticides. They appear to be ideal insecticides, but unfortunately there are major disadvantages as well.

Firstly, neonicotinoids usually are highly toxic to the number one insect pollinator on the planet. Neonicotinoid use has been strictly limited in France since the 1990s, and the French Comité Scientifique et Technique concluded in 2003 that neonicotinoids were implicated in a mass die-off of the bee population. It is believed by some to account for worker bees neglecting to provide food for eggs and larvae, and for a breakdown of the bees' navigational abilities and possibly leading to what has become generally known as Colony Collapse Disorder, which is usually associated with the mite pest Varroa destructor. In 2008, Germany banned seed treatment with neonicotinoids due to negative effects upon bee colonies. Bee keepers suffered a severe decline linked to the use of clothianidin in the Baden-Württemberg region of Germany.

The second major disadvantage of neonicotinoids is their potential to leach from soils. The widely used neonicotinoid insecticide imidacloprid is a major contaminant of Dutch surface water. Excessive imidacloprid levels in surface water - that are toxic to insects - have been noted in Western Dutch provinces with massive bee colony losses as well as intensive agriculture, such as the provinces North- and South Holland. The highest imidaclopid concentration measured in the surface water of Noordwijkerhout was nearly 25,000 times above the acceptable limit.

Recent bird monitoring data have revealed a dramatic decline in the number of grassland birds in the Netherlands and the average annual decline has more than tripled since the year 2000 when compared to the nineties, i.e. from 1.2% per annum in 1990-2000 to 4.6% from 2000-2004. There are regional differences, and decline is highest (with an average annual decline of 13%) in the Western part of the Netherlands. Particularly alarming is the steep decline of up to 30% annually of songbirds like the Skylark, Meadow Pipit and Yellow Wagtail.

The decline correlates well with major contamination of Dutch surface water with imidacloprid, which was first introduced in agriculture in 1994 and is by far the most widely used insecticide now. This evidence suggests that farmland bird decline may be caused by insect decline through environmental contamination with imidacloprid. Are we revisiting Rachel Carson's Silent Spring, half a century after DDT? Let us remember what Miss Carson wrote at the time (1962):

"For each of us, as for the robin in Michigan, or the salmon in the Miramichi, this is a problem of ecology, of interrelationships, of interdependence. We poison the caddis flies in the stream and the salmon runs dwindle and die. . . . We spray our elms and following springs are silent of robin song, not because we sprayed the robins directly but because the poison traveled, step by step, through the now familiar elmleaf-earthworm-robin cycle. These are matters of record, observable, part of the visible world around us. They reflect the web of life-or death-that scientists know as ecology. "

Miss Carson was not arguing that we should ban chemical pesticides all together, but that we should be more careful in our application of these chemicals, since all species including humans are interconnected with one another and killing one species may endanger others. Says Miss Carson: "it is not my contention that chemical insecticides must never be used. I do contend that we have put poisonous and biologically potent chemicals indiscriminately into the hands of persons largely or wholly ignorant of their potentials for harm." She explains that by trying to control these pests with chemical pesticides, we are upsetting the balance of nature. It is a battle we cannot win she says, because "as crude a weapon as the cave man's club, the chemical barrage has been hurled against the fabric of life—a fabric on one hand delicate and destructible, on the other miraculously tough and resilient, and capable of striking back in unexpected ways."

Dutch scientists and environmental organisations are now calling for an immediate ban on imidacloprid. The regulators, however, see no reason to restrict its use.

Hint for non-Dutch speaking visitors: at the bottom of the left-hand menu bar you will find links to change the interface-language of this site into English, French, German or Dutch.
You can use http://babelfish.yahoo.com/ to translate the Dutch stories into the language of your choice.