Age-related changes in the behavioural response of honeybees to Apiguard®, a thymol-based treatment used to control the mite Varroa destructor

The parasitic mite Varroa destructor is responsible for heavy losses in honey bee colonies and represents a major threat to the beekeeping industry. Essential oils offer an attractive alternative to the use of synthetic chemicals for the control of varroa. Amongst them, thymol appears to be particularly promising. However, treatments using thymol as their active substance, such as the gel formulation Apiguard(R), are suspected to have adverse effects on honey bee colonies. In this study, laboratory assays are used to investigate the effects of Apiguard(R) exposure on honey bee behaviour. Our results reveal that honey bee responses to this anti-varroa treatment change with honey bee age. While 2-day-old bees respond neutrally to Apiguard(R), older bees generally avoid the Apiguard(R) gel. Responses of forager bees were particularly striking. Foragers appear to be repelled by Apiguard(R). Touching their antennae with Apiguard(R) induces robust fanning behaviour. Our data suggest, however, that forager bees exposed to Apiguard(R) in the hive can become habituated to this treatment. These results offer interesting new perspectives on the effects of Apiguard(R) on honey bee behaviour and serve to highlight age-related changes in honey bee responses to gustatory, as well as olfactory cues.