Exposure to thymol decreased phototactic behaviour in the honeybee (Apis mellifera) in laboratory conditions

The effects of the terpenoid thymol were evaluated on the phototactic behaviour of the adult honeybee (Apis mellifera) 1 and 24 h after a topical application. The behaviour was quantified under different light intensities by measuring the time spent in the light source area and in areas opposite the source. Stimuli of 200 lx induced positive phototaxis of the bees. Thymol administered at 1 ng/bee had no effect on the phototaxic behaviour while bees that had received 10 or 100 ng thymol 1 h before the test were less attracted by the 200-lx stimulus. The effect of thymol increased when the phototaxic behaviour was tested 24 h after the topical application. However, with a light intensity of 400 lx the dose 10 ng/bee was ineffective and for 600 lx the phototaxic behaviour of the bees was not modified by the exposure to thymol.