Thymol is a natural substance increasingly used as an alternative to pesticides in the fight against the Varroa destructor mite. Despite the effectiveness of this phenolic
monoterpene against Varroa, few articles have covered the negative or side effects of
thymol on bees. In a previous study, we have found an impairment of phototaxis in honeybees following application of sublethal doses of
thymol-lower or equal to 100 ng/bee-under laboratory conditions. The present work shows the same behavioral effects on bees from
hives treated with Apilife Var®, a
veterinary drug containing 74 %
thymol, with a decrease in phototactic behavior observed 1 day
after treatment. Thus,
thymol causes disruption of bee phototactic behavior both under laboratory conditions as well as in beehives. The bee exposure dose in treated
hives was quantified using gas chromatography coupled to mass spectrometry (GC-MS), giving a median value of 4.3 μg per body 24 h
after treatment, with 11 ng in the brain. The
thymol level in 20 organic
waxes from
hives treated with Apilife Var® was also measured and showed that it persists in
waxes (around 10 mg/kg) 1 year
after treatment. Thus, in the light of (1) behavioral data obtained under laboratory conditions and in beehives, (2) the persistence of
thymol in
waxes, and (3) the high load on bees, it would appear important to study the long-term effects of
thymol in beehives.