[Thesis defence] 09/12/2025 – Pierre Le Bivic: «Water resource economy in honey bees (Apis mellifera): quantitative and qualitative aspects» (UPR Bees and Environment)

Mr Pierre LE BIVIC will publicly defend his thesis entitled: «Water resource economics in honey bees (Apis mellifera): quantitative and qualitative aspects», supervised by Mr Luc BELZUNCES, on Tuesday 9 December 2025.

Laboratory

Bees and the Environment Research Unit

Composition of the jury

Mr Luc BELZUNCES	INRAE	Thesis supervisor
Ms Christelle Adam-Guillermin	ASNR	Rapporteur
Mr Mathieu LIHOREAU	CNRS	Rapporteur
Mrs Freddie-Jeanne RICHARD	INRAE	Examiner
Mr Fabrice REQUIER	IRD	Examiner
Ms Maryline PIOZ	INRAE	Thesis co-director

Summary

Honeybee colonies (Apis mellifera) collect water mainly for thermoregulation of the brood and to produce larval jelly. While the mechanisms that regulate water collection in honeybees are well described, the water requirements of colonies remain poorly documented. However, the availability and quality of this resource are now threatened by climate change and the risk of pollution with substances that are toxic to bees. A better understanding of the relationship between honey bees and water resources will enable us to anticipate the colonies' ability to adapt to these threats. To this end, we (i) quantified the influence of meteorological and population factors on the volume of water collected daily by colonies, as well as on the proportion of water foragers in the colony, (ii) studied the water preferences of bees, and (iii) tracked the fate of water in the colony to study the effect of temperature on the different uses it makes of this resource. Our results revealed two thresholds. The first identifies the outside temperature at which the amount of water collected by the colony increases sharply to ensure the thermoregulation of the brood. The second gives us the size of the colony at which we assume a higher level of specialisation among water foragers, suggesting a better thermoregulatory capacity for the colony. We then showed that, under conditions of choice, the outside temperature does not influence the bees' water preferences and that these decrease monotonically with increasing water mineralisation. Finally, we estimated the amount of water consumed by the bees, the amount used to produce larval jelly, and the amount used to regulate the brood's temperature. These results lead us to question whether there is a limit to the amount of water a colony can collect to cope with a heatwave. This work paves the way for a better understanding of the relationship between honey bees and water resources, and provides practical information to help beekeepers cope with the climatic, health and social challenges affecting this resource.

Keywords : brood, deuterated water, larval jelly, homeostasis, threshold, temperature