The importance of using healthy bees in toxicity studies has not been discussed. If the bees used in the study are weakened or ill the results can be quite different from those using healthy bees.

> Midgut metabolism is important in the detoxification of chemicals in the honeybee. … The health of the midgut is therefore key in the detoxification following oral exposure. Therefore, the sensitivity to pesticides by ingestion may differ if disease or other pesticides are present. This may provide some explanation for the oral toxicity of imidacloprid in this study being 2 orders of magnitude lower than the published value while the contact LD50 was similar to published values.

> Factors may include feeding honey from emergence rather than sucrose alone as prophylactic induction of P450s may occur through consumption of pollen and honey flavonoids enhancing bee survival (Johnson 2008). Understanding the impact of mixtures on toxicity following oral exposure is important despite the paucity of studies on this more realistic route of exposure where residues are present in pollen and nectar.

> In assessing the impact of the data, it should be remembered that reported levels of neonicotinoid seed treatments in nectar and pollen are usually <20 μg/kg, and therefore, exposure to an acutely toxic dose even at the maximum synergy observed is unlikely. Foraging bees are exposed via ingestion of contaminated nectar but consume virtually no pollen, and pollen intake is low in other adult bees within the hive

Potential impacts of synergism in honeybees (Apis mellifera) of exposure to neonicotinoids and sprayed fungicides in crops
Apidologie (2014) 45:545–553

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