Identification of five volatile organic compounds that trigger hygienic and recapping behaviours in the honey bee (Apis mellifera)

Varroa destructor, the main parasite of the honey bee (Apis mellifera), is having a devastating effect on beekeeping worldwide. The development of resistance traits in some colonies, linked with Varroa-sensitive hygiene (VSH) and recapping (REC) behaviours, provide an ideal avenue for long-term sustainable control of the parasite. The most important step in these behaviours is the detection of parasitized brood cells. Several semiochemicals released from Varroa-infested brood cells, targeted by VSH behaviour, trigger this behaviour. Most of these compounds are not very volatile. In the current work, we focus on the study of volatile organic compound (VOC) emissions from Varroa-infested cells. This study describes the emission of nine VOCs characteristic of Varroa parasitism, of which five could be identified and triggered hygienic and recapping behaviours. These five compounds were also tested with compounds already described in the literature, in relation to the volatile nature of the compounds. Using solutions containing 1-15 compounds, we looked at the cleaning and recapping behaviours of the workers. Behavioural results highlight the importance of the VOCs found in this study in the detection, opening and recapping of brood cells, while low volatile compounds seem to play a particularly key role in the sacrifice of pupae. Similar to the Varroa parasitization-specific (VPS) compounds, including the tetracosyl acetate alone, the cleaning of brood cells triggered by one of the compounds identified in this study, n-tetradecane, appears to be linked to the colony's ability to carry out VSH behaviour. This study opens new perspectives in the understanding of resistance behaviour of honey bees against their main parasite Varroa destructor.