Insights into the defence of honey bees, Apis mellifera L., against insecticides

There are some contradictory theories on how tolerant honey bees are of pesticides. Since the honey bee genome has been published (Honey bee Genome Sequencing Consortium, 2006), more is known about their metabolic systems, especially the detoxification pathways for potential xenobiotics. Bioassay and biochemical data from various studies have shown that both P450s and carboxylesterases are responsible for pesticide metabolism in honey bees. Here, those metabolic enzymes that confer primary defence to different classes of insecticides in honey bee were validated. Metabolic enzymes are characterised regarding their ability to interact with the insecticide. Synergist bioassay results with PBO and EN 16/5-1 suggest that detoxification mechanism(s) play an important role in protecting honey bees from selected insecticide toxicity. No binding was found between honey bee esterases and tested insecticides, whilst inhibition of P450 activity sensitised the honey bees to these chemicals. Metabolism of tau-fluvalinate and thiacloprid in honey bees is reportedly due to P450 activity, but this metabolism may not be the only reason for the relatively benign action of this insecticide on bees. Honey bees are less sensitive to neonicotinoids containing a cyanoimino pharmacophore than to those with a nitroimino group, however the specific enzymes involved in detoxification remain to be characterised. In this work, pre-treatment of honey bees with a sub-lethal dose of an insecticide induced protection to the same compound. Transcriptome profiling, using microarrays, identified a number of genes encoding detoxification enzymes that were overexpressed significantly in insecticide-treated bees compared to untreated controls