Scientific note on the potential beneficial effect of 1-octen-3-ol on the survival of Apis mellifera chronically exposed to low doses of fipronil.

Fipronil, a non-competitive antagonist of gamma-aminobutyric acid receptors (GABA-Rs), inhibits the flow of chloride ions in the nerve cells, leading to the insect death. In a previous work, the volatolome of bees chronically exposed to this insecticide (0.5 and 1 ug/L) was analyzed and characterize the Apis mellifera metabolic responses. Two Volatile Organic Compounds or VOCs (1-octen-3-ol and 2,6-dimethylcyclohexanol) produced by bee were highlighted. We assumed that these VOCs could act as modulators of the GABA-R to counteract the effect of fipronil. The toxicity of these VOCs was tested on emerging bees for concentrations ranging from 0 to 3.4 ug/L. Survival and the sucrose consumption were recorded during 21 days of chronic exposure. 1-octen-3-ol and 2,6-dimethylcyclohexanol did not significantly affect the proportion of survival at the end of the experiment, whatever their concentration. 1-octen-3-ol (0.5, 1, 1.7 and 3.4 ug/L) was chosen to assess its effect in the case of co-exposure with fipronil (0.5 and 1 ug/L). A beneficial effect on survival at 21 days was observed with an average improvement in survival rate for the co-exposed groups. This positive effect was not related to the VOC concentration and could be a direct effect (interaction with GABA-R) or a hormetic effect (global improvement of bee fitness).