Synergistic interactions between a variety of insecticides and an ergosterol biosynthesis inhibitor fungicide in dietary exposures of bumble bees (Bombus terrestris L.)

BACKGROUND: In recent years, concern has been raised over honey bee colony losses, and also among wild bees there is
evidence for extinctions and range contractions in Europe and North America. Pesticides have been proposed as a potential
cause of this decline. Bees are exposed simultaneously to a variety of agrochemicals, which may cause synergistically detrimental
impacts, which are incompletely understood. We investigated the toxicity of the fungicide imazalil in mixture with
four common insecticides: fipronil (phenylpyrazoid), cypermethrin (pyrethroid), thiamethoxam, and imidacloprid (neonicotinoids).
Ergosterol biosynthesis inhibitor (EBI) fungicides like imazalil can inhibit P450 detoxification systems in insects and
therefore fungicide−insecticide co-occurrence might produce synergistic toxicity in bees. We assessed the impact of dietary
fungicide−insecticidemixtures on the mortality and feeding rates of laboratory bumble bees (Bombus terrestris L.).
RESULTS: Regarding mortality, imazalil synergised the toxicity of fipronil, cypermethrin and thiamethoxam, but not imidacloprid.
We found no synergistic effects on feeding rates.
CONCLUSION: Our findings suggest that P450-based detoxification processes are differentially important in mitigating the
toxicity of certain insecticides, even those of the same chemical class. Our evidence that cocktail effects can arise in bumble
bees should extend concern about the

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