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

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
Interactions between neonicotinoids and disease (update EFSA review)
Honeybees are known to suffer from a wide array of bacterial, fungal and viral pathogens as well
as ecto- and endo-parasite. Multiple infections are common and the impact of some pathogens can
be far higher in the presence of other associated pests and diseases. Honeybees have a well-
developed immune system for coping with bacterial and fungal infections although their immune
response to viral pathogens is less well understood and there has been significant interest recently
on the potential for pesticides to affect the susceptibility of bees to diseases. This has been
highlighted by high pesticide residues reported in honeybee colonies in the USA and the
importance of microbial communities within the hive which may be affected by pesticide residues
as well as impacting on the bees directly.
The dense crowding within social and eusocial bee colonies together with the relatively
homeostatic nest environment with stored resources of pollen and nectar/honey results in
conditions conducive to increased susceptibility to disease. This has resulted in the evolution of
both individual and social immunity in the honeybee and bumble bee
Factors other than pesticides can impact on the immune system in honeybees and increase
susceptibility to disease, e.g. other diseases, the immunsuppressive effects of Varroa destructor,
antibiotics, sulphonamides and metals and immunostimulators have been proposed. Confinement
of colonies can result in immune suppression and oxidative stress in colonies and poor habitat
quality may result in lowered immune response. One key factor is that although colonies show
qualitatively similar immune responses the colony is a significant factor in the level of the response,
i.e. there are large variations between colonies on the level of the response. There have also been
suggestions that stress, e.g. isolation, weakens individual immunocompetence. This may explain
Neonicotinoid pesticides and bees Page 5 of 133
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