Bijensterfte, oorzaken en gevolgen

New research by Prof. Vincenzo Girolami of the University of Padova in Italy shows Neonicotinoids in maize kill bees via water droplets. The same seed-dressed imidacloprid maize as the one used in this experiment is widely grown in the Netherlands.

Here you can see a video clip of the effects:

(Source: http://dl.getdropbox.com/u/521609/provaapi.wmv, Needs Windows Media Player - sometimes the video-streaming on this site is too slow, you can right-click the link above and chose "Save target as..", to download the video to your harddisk and watch it offline.)

Highly toxic neo-nicotinoid insecticides such as Clothianidin and Imidacloprid were permitted for agricultural use in Germany, but only on the basis that bees would not be exposed to these substances. It was argued that bees would not be poisoned because these pesticides would only be used for the coating of seeds - and safely buried underground. However, current research in the wake of the massive bee deaths in Germany after maize-sowing in the spring of 2008 gives serious cause for concern.

Many thousands of bee colonies were killed by direct contact withClothianidin or Imidacloprid dust which escaped from maize-seeds during planting - as a result of abrasion in the seed drill, due to dry soil and windy conditions, which allowed the pesticide to escape into the environment during planting.

However, Professor Girolami’s research has demonstrated that the resulting maize plants themselves present a danger to bees. For several weeks the plants, growing from the pesticide-coated seeds, represent a danger to bees through their expression of ’guttation droplets’ and the dew on their leaves, both of which provide sources of liquid that forager bees collect to drink.

’Guttation’ is the appearance of drops of plant-sap on the tips or edges of leaves of some vascular plants, such as grasses - (including maize, wheat, barley etc). At night, transpiration of water by plants into the atmosphere usually stops because most plants close their stomata. When there is a high soil-moisture level, water will enter plant roots, because the osmotic pressure of the plant-roots is lower than that of the water and salts in the soil. The water will thus pass from the soil into the plant, creating a positive pressure. This increased pressure within the plant forces some water to be exuded through special leaf-tip or edge structures, called ’hydathodes’, forming drops of sap/ water on the leaves. And because Imidacloprid, Clothianidin and other neo-nicotinoid pesticides are systemic - and present in the rising sap of the plants - the pesticides are expressed in these droplets.

Current research by Prof. Vincenzo Girolami of the University of Padova in Italy has shown that neonicotiniods such as Imidacloprid used to coat the seeds at planting time - are present in the plant’s guttation water. The first drops which emerge from the plant show insecticide concentrations of 10 – 100 pp million – - roughly a thousand times higher than the levels found in Maize pollen and nectar.

Such doseages would kill any insect which drinks this water. The mean lethal oral dose of Imidacloprid for bees is approx. 150 pp billion per bee. - so these concentrations are roughly a thousand times the dose which is lethal to bees.

Maize plants grown from pesticide-coated thus seeds pose a danger to bees for several weeks. Once the plants have grown to about 40 cm, they seem to be less hazardous for insects. Prof. Girolami’s field trials and lab tests from 2008 both confirm that bees, which drink ’guttation water’ with the above-mentioned neonicotinoid concentrations die almost immediately - within 2–5 minutes.

The Germany Professional Beekeepers Association (DBIB) regards the use of neonicotinoid seed-coatings as a violation of the legal protection accorded to bees under BienSchV (bee protection ordinance 1992) The Association has asked for urgent independent research into the issue and has called for an immediate halt to the use of all neonicotinoid seed-coatings for maize and summer cereals.

From Karl Maresch - German Professional Beekeeping Association

Source: http://www.farminguk.com/news/Bees-killed-by-Neo-nicotinoids-in-expressed-Maize-sap10986.asp

Zie ook http://www.vkblog.nl/bericht/242514/Bijensterfte%2C_de_oorzaak%3F

In Nederlands is zaadbehandeling van maïs met imidacloprid sinds 1995 toegestaan:
http://www.ctb.agro.nl/ctb_files/11601_01.html
Inmiddels wordt het ook op grote schaal toegepast in Nederland.

Een vergelijkbaar middel thiamethoxam is toegelaten als insectenbestrijdingsmiddel door middel van zaadbehandeling van snijmaïs en korrelmaïs sinds 10 mei 2007.

In Duitsland, Frankrijk, Italie en Slovenie is het gebruik van imidacloprid voor zaadbehandeling van maïs vanwege de gevaren voor de bijen verboden. Andere toepassingen van deze middelen zijn onder restricties nog wel toegelaten.

Voor een reactie van Bayer op het onderzoek, zie:
http://www.bayercropscience.com/BCSWeb/CropProtection.nsf/id/EN_20090302
"At these early growth stages, which are most relevant for guttation of maize, the young plants are just a few centimeters tall and can be ruled out as a source of food for bees. Thus it is not correct that Professor Girolami has identified guttation as a cause of bee deaths.", aldus Bayer.