Neonicotinoid Pesticides and Bees - The Food and Environment ...

2.3.1 Conclusions
Pesticides widely used both in the agricultural and urban environment (pest control and
home and garden uses) as well as by beekeepers to control pests, e.g. fluvalinate, amitraz,
coumaphos to control varroa, are detectable in bees and hive matrices. Exposure of
honeybees to any single pesticide application may occur over the short term or, unlike many
organisms, over a longer period if residues are present in pollen and/or nectar stored within
the colony or due to migration of lipophilic compounds into wax. These more persistent
residues are likely to be available to the colony over a period of time depending on the active
ingredient and the frequency of use, e.g. multiple applications.
Bees may be exposed to mixtures of products applied to plants on which they forage.
Recent data indicates the extent of mixing of formulations that occur on arable, vegetable
orchards and soft fruit crops in the UK and includes tank mixing of EBI fungicides with
neonicotinoid insecticides. In addition to the application of products as tank mixes, the
increasing use of seed treatments raises the possible scenario of nectar, pollen or guttation
water containing active ingredients also being contaminated with sprays applied during the
flowering period, e.g. oilseed rape.
Although many reports of residues in pollen being returned to the hive by foragers are
published the majority of these are based on individual pesticide residues rather than
assessments of the total pesticide residue levels and the data are often not reported in
sufficient detail to determine the residue levels of the individual components within multiple
detections.. Data reported for residues of chemicals applied by beekeepers in honeybee
colonies have primarily been directed at single varroacides with some limited data after
antibiotic dosing. Those that are available show that very high levels of varroacides may be
present within colonies and are regularly detected in live bees
The risk from most mixtures can be assessed using the additive approaches of
concentration addition (or dose addition) and independent action (IA). In identifying the
relevance of synergy in determining the toxicity of mixtures it is important to understand the
route of metabolism of pesticides in honeybees and the effects of age, season etc on this.
The role of oxidative metabolism in detoxification of the cyano-substituted neonicotinoids in
bees is highlighted by the increase in toxicity of acetamiprid and thiacloprid in combination
with the EBI fungicides. The majority of synergistic effects observed in honeybees have
been ascribed to inhibition rather than induction of P450s involved in pesticide metabolism.
The level of exposure to the synergist also affects the scale of the synergy. The effect of
exposure on the scale of synergy is important as many of the laboratory studies have been
undertaken with high doses of synergists, e.g. 3-10 µg/bee and at more realistic exposure
levels such high increases of toxicity have not been observed even under laboratory
conditions. Contact and oral dosing with combinations of a range of EBI fungicides at more
realistic exposure levels with neonicotinoid insecticides showed only low levels of synergy.
There are no reports of interactions between varroacides and neonicotinoid pesticides but
recent data suggest that antibiotics used in colonies may affect susceptibility to both
varroacides and other pesticides
Neonicotinoid pesticides and bees Page 39 of 133
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