Abstract
Bees
are essential pollinators of many plants in natural ecosystems and
agricultural crops alike. In recent years the decline and disappearance
of bee species in the wild and the collapse of honey bee colonies have
concerned ecologists and apiculturalists, who search for causes and
solutions to this problem. Whilst biological factors such as viral
diseases, mite and parasite infections are undoubtedly involved, it is
also evident that pesticides applied to agricultural crops have a
negative impact on bees. Most risk assessments have focused on direct
acute exposure of bees to agrochemicals from spray drift. However, the
large number of pesticide residues found in pollen and honey demand a
thorough evaluation of all residual compounds so as to identify those of
highest risk to bees. Using data from recent residue surveys and
toxicity of pesticides to honey and bumble bees, a comprehensive
evaluation of risks under current exposure conditions is presented here.
Standard risk assessments are complemented with new approaches that
take into account time-cumulative effects over time, especially with
dietary exposures. Whilst overall risks appear to be low, our analysis
indicates that residues of pyrethroid and neonicotinoid insecticides
pose the highest risk by contact exposure of bees with contaminated
pollen. However, the synergism of ergosterol inhibiting fungicides with
those two classes of insecticides results in much higher risks in spite
of the low prevalence of their combined residues. Risks by ingestion of
contaminated pollen and honey are of some concern for systemic
insecticides, particularly imidacloprid and thiamethoxam, chlorpyrifos
and the mixtures of cyhalothrin and ergosterol inhibiting fungicides.
More attention should be paid to specific residue mixtures that may
result in synergistic toxicity to bees.
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