Imidacloprid effects on bee population

Imidacloprid is a systemic insecticide produced by the chemical firm Bayer AG. In France it was sold under the name Gaucho and its use is highly controversial as it is believed to be responsible for high losses in bees. According to the National Union of French Beekeepers (UNAF), the number of hives in France has plummeted to one million in 2003, from 1.45 million in 1996. Between 1995 and 2001, the average production of honey went from 75 kg/hive down to 30 kg/hive. The AFFSA (equivalent of the US FDA) indicate the national production went down from 40,000 tons to 25,000 tons per year.

French beekeepers claim that Imidacloprid, as a seed treatment for sunflowers, has killed many bees and caused a significant drop in honey production. Some requested that systemic insecticides uses be withdrawn from crops where bees might be affected, while others called for a complete ban on its use.

Initial observations of bees decline
In France, Imidacloprid started being used in 1994 as a seed-coating for sunflowers. The following years, some beekeepers mentioned the possibility of a relationship between the pesticide and some behavioral troubles in bees. Bayer CropScience made some studies on the topic, which concluded Gaucho was non-toxic to bees. At this point, most discussions were kept rather private between Bayer and beekeeper associations.

However, during summer 1997, heavy losses of bees were observed in several regions of France and the controversy became public.

1998 : estimation of Imidacloprid toxicity
In 1998 a French official study was conducted with the goal to determine whether Imidacloprid was responsible for the bee population decrease, as well as the reduction in honey production during the flowering season of sunflowers.

Ecotoxicology studies had to define the living being in danger (the bees), to define the chemical concerned (imidacloprid), to evaluate the quantity necessary to kill the living being with the chemical, and to define the concentrations at which there is no detrimental effects on the living being.

In the case of the accusations against Imidacloprid, the issue is not the direct death of the bees, but behavioral changes such as disorientation, feeding problems, and communication disturbance. Initial studies were aimed at determining the minimal amount for which bees showed these behavioral changes.

The study, led by AFSSA, in four different areas showed no differences in terms of bees behavior, mortality, evolution of the beehives, and honey harvest with or without Imidacloprid.

A study led by Wilhelm Drescher in 1998 from the University of Bonn on the activity of bees in sunflower fields in western France concluded that no results could prove Imidacloprid, used on sunflower seeds, had a detrimental effect on bees. It also mentioned that other possibilities, such as viral diseases vectored by Varroa mites (the populations of such being on the rise since 1996 due to appearance of resistance to acaricides). It essentially concluded that the French bee loss was not linked to imidacloprid but to a viral disease or a spiroplasma in bees which produces similar symptoms.

In parallel several studies have been conducted by Bayer CropScience to evaluate the risk for bees related to the use of Imidacloprid on sunflowers.

Bayer claimed that several studies had been made in open air as well as in greenhouses in Argentina, Canada, Germany, France, Great Britain, Italy, Sweden, South Africa, Hungary, and the United States, and that all those studies confirmed Imidacloprid was not dangerous to bees.

Bayer also claimed that other arguments may be provided to explain the loss of bees. They indicated that in a study led in 1975 (Wilson, Menapace), bee decline had been obverved in 27 American states. Most disappearances were seen in wet and fresh spring. Inspectors mentioned a disease, famines, unusually wet and fresh weather, diarrhea, lack of pollen, dead queens, genetic defaults, and stress.

Another study by Kulincevic et al. in 1983 mentioned that the primary reason for malnutrition in bees is an insufficient pollen offer. It was mentioned that modern techniques could help by offering food substitutes to bees, but that poor substitutes (such as soy) could provoke bees' decline.

Imidacloprid banned as a sunflower seed treatment in 1999
Finally, Jean Glavany, Minister of Agriculture in the French government, used the precautionary principle and decided to withdraw the use of imidacloprid as a sunflower seed treatment in 1999. Bayer scientists denied again that the product was responsible for the colonies' death in a meeting in 2000.

Jean Glavany renewed the ban in 2001 for two additional years and asked a panel of experts to make a complete epidemiological study to try to figure out all the factors that might explain bees' decline, still observed during these years.

Second set of studies in 1999 and 2000
At the end of 1998, studies indicated there were no effects, but doses were very small and unmeasurable in the laboratory. A second set of studies was lauched in 1999, to quantify:
 * toxicity of the product (imidacloprid) on bees
 * remanence of the product in soil
 * quantities in plants

Bayer CropScience results show that the maximal dose for which no effect was observed was 20 ppb, while the amount of residue in parts of the plant available to the insect (aerial parts) was below 1.5 ppb. They concluded bees could not be in contact with high enough concentrations to be able to be affected by the pesticides, and that the sunflower seed treatment was risk-free for bees.

The "Commission des Toxiques" brought these conclusions in 2001:
 * imidacloprid answers European legislation in terms of soil remanence, and does not accumulate in soils
 * residues may be found in plants cultivated after a sunflower whose seeds where treated by Imidacloprid. Residues were found only in parts to which bees are not exposed (such as leaves). No residue was found in the pollen of untreated sunflowers.

The commission concluded that it had no serious indicators suggesting Imidacloprid might be dangerous to bees. However, the commission suggested a risk could exist with seed-treated corn pollen.

Gerard Eyries, marketing manager for Bayer's agricultural division in France, was cited saying studies confirmed that Imidacloprid left a small residue in nectar and pollen, but there was no evidence of a link with the drop in France's bee population, adding, "It is impossible to have zero residue. What is important is to know whether the very tiny quantities which have been found have a negative effect on bees." He also added that the product was sold in 70 countries with no reported side effects.

Other studies indicated that concentrations were especially high when the plant is young. These would often be of
 * 10 to 20 ppb in upper leaves
 * 100 to 200 ppb in other leaves
 * less than 1.5 ppb in nectar
 * 2 to 3 ppb in pollen

Bayer then agreed that the insecticide may cause disorientation of bees at levels above 20 parts per billion of the active ingredient. Recent studies by researchers at the Institut National de la Recherche Agronomique (INRA) suggest that bee behaviour is affected at levels between 3-16 ppb or possibly even 0.5 ppb.

Current situation of bees' decline
In 2001, Bayer also brought a judicial case against Maurice Mary, one of the leaders of the French association of beekeepers for disparagement of the chemical Imidacloprid. The action was dismissed by the judge in May 2003.

In 2003, agricultural Minister Jean Glavany again extended the suspension of the use of Imidacloprid on sunflower seeds.

In spite of a 4 year ban already on sunflower seeds treatment, a significant drop in bee individuals is still observed. Beekeepers were cited as saying the measure was insufficient, as studies found that Imidacloprid left a residue which meant that even after two years, plants sowed on the same spot as the crop originally treated contained traces of the product.

Some also suggest that the bee colony losses could also be due to the use of imidacloprid on corn as well, or by the replacement of it by another systemic insecticide called Fipronil. Indeed in May 2003, the DGAL (Direction Générale de l'Alimentation du ministère de l'Agriculture ) indicated death of bees observed in the south of the country had been caused by acute toxicity by Fipronil (as the active chemical in the systemic insecticide called Regent), while it was recognised Imidacloprid had no responsibility in the bees death. Some national field studies are currently under way (2003) to assert the responsibility of Imidacloprid.

A similar battle is occurring in Nova Scotia, where beekeepers are accusing Imidacloprid used on potatoes for massive losses of bees needed for blueberry pollination.