[Thesis defense] 4 May 2023 - Amélie Noël: "Chemical ecology of the behavioural defence of the honey bee (Apis mellifera) against the parasite Varroa destructor", Laboratory UR406 Bees & Environment - INRAE PACA, Avignon

Date and place

4 May 2023 at 14:00
Avignon University, Jean-Henri Fabre Campus, CERI, Amphi Blaise

Discipline

Agricultural sciences

Laboratory

Laboratory UR406 Bees & Environment - INRAE PACA, Avignon

Framing

Dr. Yves Le Conte & Dr. Fanny Mondet

Composition of the jury

• Pierre Giovenazzo, PR, University of Laval, Quebec - Rapporteur
• Anne-Geneviève Bagnères-Urbany, DR-HDR, CNRS, CEFE, Montpellier - Rapporteur
• Freddie-Jeanne Richard, MCF-HDR, CNRS, EBI, University of Poitiers, Poitiers - Examiner
• Jean-Christophe Sandoz, DR-HDR, CNRS, EGCE, Gif-sur-Yvette - Examiner
• Yves Le Conte, DR-HDR, INRAE, A&E, Avignon - Thesis Director
• Dr. Fanny Mondet, IPEF, INRAE, A&E, Avignon - Thesis co-director

Summary of the thesis

Varroa destructor is a global threat to the honey bee (Apis mellifera) and beekeeping. The infestation of a colony with varroa mites can, within a few months and without treatment, compromise its survival. However, some colonies have developed resistance to the parasite and are able to regulate the growth of the varroa population within the colony. This resistance is based on various traits, including VSH behaviour (Varroa Sensitive Hygiene) and the reoperculation behaviour of brood cells. These two hygienic behaviours involve (i) the detection of parasitized brood cells, (ii) the opening and then (iii) the choice in the fate of these brood cells. Depending on this choice, the brood is sacrificed and the cell emptied of its contents (VSH) or it is re-operculated leaving the brood intact (re-operculation). The mechanisms underlying the choice between these behaviours are not well understood but require the emission of a semiochemical message, the detection and neural processing of this message by the workers and the appropriate behavioural response. In the scientific literature, ten compounds have been identified as triggering VSH behaviour, and no compound has been identified as triggering re-operculation behaviour. Only two of these compounds are characterised as Volatile Organic Compounds (VOCs).

It is assumed that compounds of different volatility (VOCs and low volatile compounds) are involved in VSH and re-operculation behaviour. The VOCs are thought to propagate rapidly through the wax seal signalling parasitism and the less volatile compounds are thought to allow accurate identification of the parasitized cell. The objective of this thesis is to deepen the knowledge on the hygienic behaviour involved in the resistance of honey bee colonies to the parasite Varroa destructorThis is being done by studying the VOC emissions in the context of healthy brood development and varroa parasitism, and the behaviour of workers with respect to all compounds identified as characteristic of the brood parasitism. To this end, VOC emissions are studied in the context of healthy brood development and in the context of varroa parasitism, and the behaviour of workers towards all the compounds identified as being characteristic of parasitised brood is tested. This thesis demonstrated the emission of 32 VOCs during healthy brood development and nine VOCs characteristic of varroa parasitism, of which five could be identified. The behavioural results underline the importance of VOCs in the detection, opening and re-operculation of brood cells, while low volatile compounds seem to play a particularly central role in pupal sacrifice. This study opens new perspectives in the understanding of these two resistance behaviours of honey bees against their main parasite Varroa destructor.

Keywords : Varroa destructorChemical communication, volatile compounds, resistance, VSH, reoperculation.