Wetenschap - 15 april 2013

Toxicity tests on bees below standard

EFSA dissatisfied with bee field tests.
Very little reliable information about bees and insecticides.

Were the bee deaths in the winter caused by neonicotinoids? No, said a vast majority of those present at the 'Buzzing Toxicity' bee symposium in the Forum last Friday. The meeting was initiated by KNCV (chemists), NVT (toxicologists) and KNM, a knowledge-based network on the environment. But much remains unclear when it comes to bees and insecticides from the neonicotinoid family.
Take the 'lethal dose' (the LD50 value) for a substance such as imidacloprid. For honey bees, this lies between 3 and 81 nanogrammes per bee. This is rather inaccurate, says ecotoxicologist Kees van Gestel (professor of Ecological Sciences) of the VU University. Van Gestel says that this is because bees have different sensitivity levels in the various stages of their life. One bee is different from another. There is no dispute that neonicotinoids are very toxic for bees, says Van Gestel. 'But the effects observed in the field are not that bad. Observations made in the laboratory often do not tally with those in the field.'
But the field tests do not give a complete picture either, comments toxicologist Robert Luttik. His is the vice-chairman of the European Food Safety Authority (EFSA) panel which assesses the risks of pesticides. According to him, the prescribed toxicity tests are too limited. For example, the severe exposure of eggs, larvae or pupae to neonicotinoids was not looked into. Neither were the effects from using several insecticides simultaneously considered.
According to Luttik, the tests carried out made use of too few hives. 'To show an effect of 35 percent with the normal confidence intervals, you would need to have as many as 74 hives. Therefore, to show a smaller effect would require even more hives.' This would never have been possible in practice. The EFSA is now drawing up new guidelines for toxicity tests.
Ivo Reossink of Alterra also questions if the honey bee is the right yardstick for testing the toxicity of substances for pollinators. The honey bee is not the most sensitive pollinator, according to his research into the sensitivity of various bees. 'The honey bee can be used as a reference, but you then need correction factors as well.'