Hi All,

Two abstracts of interest from the 2006 EurBee conference



Intoxication of honeybees - interactions of plant protection products and other factors

Martina Wehling, Werner von der Ohe, Dietrich Brasse, Rolf Forster

LAVES Institut für Bienenkunde Celle, E-mail: martina.janke©laves.niedersachsen.de

In recent years colony losses reiterated in Germany. Besides Varroosis many other causes like other bee diseases, nutrition supply as well as effects of pesticides have been discussed.

A chronic feeding study was conducted to find any indications to what extent negative effects of pesticides in sub-lethal doses can be defined from effects of other stressors (pathogens, drugs, mix of plant protection products, malnutrition of proteins) or if there will be found any interactions or coactions.

In screening programme effects of chronic dietary exposure to sub-lethal doses of the insecticide imidacloprid were studied in honeybees being loaded with a potential stressor (Varroa destructor, Nosema apis, drugs, lack of pollen supply). The results confirm a chronic oral toxicity of imidacloprid at concentrations which have in several previous studies reported to be toxic to bees (100 ppb). However, no indications were found for significant differences in sensitivity to imidacloprid between bees being loaded with different stressors and control bees.

Results confirm previous findings that optimizing of protein supply can soften negative effects of stressors. In addition it became apparent that bees from different colonies of the same apiary which were fed in parallel varied in sensitivity.

Semi-field experiment was conducted to asses the risks of mixing plant protection products by simulating commercial application during blooming on bee colonies foraging in commercial seed dressed rape with potential residues in nectar and pollen.

No adverse effects on mortality or on development of exposed bee colonies had been found when bees foraged on rape of dressed seeds and plants were sprayed with one single plant protection product alone (pyrethroid resp. azol-fungicide) or in combination (tank mix pyrethroid plus azol-fungicide).

From the findings of chronic feeding tests and semi-field test it can be concluded that imidacloprid used as standard seed dressing formulation will pose no risks to honeybees.

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Imidacloprid and bee mortality in France

M. Aubert, J.-P.Faucon, A.-C.  Martel and  M.-P.Chauzat 

AFSSA, E-mail: m.aubert©afssa.fr

In 1997, several beekeepers reported that colony death and weakness were the consequence of the use of imidacloprid for seed dressing. This product is indeed very toxic for bees as confirmed by laboratory and semi-field tests. However, several field studies were conducted in France and elsewhere with colonies kept close to cultures issued from seeds dressed with imidacloprid. None has shown any adverse effect of this product. This has been confirmed by some bee-keepers that testified that they suffered no adverse effect from such cultures. Additionally, observations in France revealed imidacloprid in pollen loads of several surveyed apiaries with no acute adverse effects on them.

An expert panel gathered by the French Ministry of agriculture studied several scenarios of contamination of bee colonies by imidacloprid. Experts concluded that several PEC/PNEC ratios were very preoccupying. However the experiment we had conducted on colonies for mimicking the natural consumption of contaminated nectar (the most risky scenario according to the expert panel) did not show any adverse effect on the tested colonies. This apparent discrepancy probably originates from the security margins used in the above mentioned risk analysis.

We conclude that, if contamination by imidacloprid from sunflower cultures issued from treated seeds may have occurred simultaneously with a period of colony losses as described by several French bee-keepers, such occurrence has not been observed systematically, and no negative impact on bee colonies of the use of Gaucho® has been experimentally demonstrated in the field.

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