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

Abstract

There are some contradictory theories on how tolerant honeybees are of pesticides. Since the honeybee 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 phase 1 detoxification enzymes (P450s and carboxylesterases) are responsible for pesticide metabolism in honeybees. Here, those metabolic enzymes that confer primary defence to different classes of insecticides (mainly neonicotinoid, thiacloprid) in honeybee were validated. Metabolic enzymes were characterised regarding their ability to interact with the insecticide. No binding was found between honeybee esterases and tested insecticides (tau-fluvalinate, α-cypermethrin, imidacloprid and thiacloprid). Metabolism of tau-fluvalinate and thiacloprid in honeybees 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. Honeybees 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 honeybees with a sub-lethal dose of thiacloprid induced protection to the same compound immediately following thiacloprid feeding. Transcriptome profiling, using microarrays, identified a number of genes encoding detoxification enzymes that were overexpressed significantly in insecticide-treated bees compared to untreated controls. These included four candidate P450s, CYP6BE1, CYP305D1, CYP6AS5, CYP315A1 and an esterase CCE8. The four P450s and cytochrome b5 were functionally expressed in Eschericia coli and their ability to metabolise thiacloprid examined by LC-MS analysis. There was no obvious metabolism of thiacloprid, thus their role in the metabolism and disposition of thiacloprid is still unclear. CCE8 expression was not achieved using the E. coli expression system.

The main findings from this research were published in Insect Molecular Biology, Volume 25, Issue 2, April 2016 (pages 171-180)