Coping with the cold and fighting the heat: thermal homeostasis of a superorganism, the honeybee colony

Abstract

The worldwide distribution of honeybees and their fast propagation to new areas rests on their ability to keep up optimal ‘tropical conditions’ in their brood nest both in the cold and in the heat. Honeybee colonies behave like ‘superorganisms’ where individuals work together to promote reproduction of the colony. Social cooperation has developed strongly in thermal homeostasis, which guarantees a fast and constant development of the brood. We here report on the cooperation of individuals in reaction to environmental variation to achieve thermal constancy of 34–36 °C. The measurement of body temperature together with bee density and in-hive microclimate showed that behaviours for hive heating or cooling are strongly interlaced and differ in their start values. When environmental temperature changes, heat production is adjusted both by regulation of bee density due to migration activity and by the degree of endothermy. Overheating of the brood is prevented by cooling with water droplets and increased fanning, which start already at moderate temperatures where heat production and bee density are still at an increased level. This interlaced change and onset of different thermoregulatory behaviours guarantees a graded adaptation of individual behaviour to stabilise the temperature of the brood.

Convergent Loss of Prothoracicotropic Hormone, A Canonical Regulator of Development, in Social Bee Evolution

“…Our hypothesis is based on the following lines of evidence, in addition to the patterns of loss of PTTH and Torso that we detected. Most eusocial bees live in cavities or other spaces where abiotic cues, such as light, are relatively limited, and where other conditions, such humidity and temperature, are tightly regulated by social group members (Danks, 2002;Stabentheiner et al, 2021). Temperature in particular is highly controlled in eusocial bee nests, where thermal conditions of developing brood are maintained by close contact with incubating adults (Heinrich, 1972;Engels et al, 1995;Bujok et al, 2002).…”

The widespread trade in stingless beehives may introduce them into novel places and could threaten species

“…behaviour, physiology) to tolerate wide climatic fluctuations. As a result, they show poor nest thermoregulation strategies and, therefore, their colonies may suffer physiological stress if they were introduced into regions with both extremely cold and/or hot climates (Jones & Oldroyd, 2006; Stabentheiner et al., 2021). In addition, stingless bee workers flying under air temperature over their thermal toleration may face body overheating with critical or lethal consequences (Macías‐Macías et al., 2011; Macieira & Proni, 2004; Souza‐Junior et al., 2020).…”

Effect of climate on strategies of nest and body temperature regulation in paper wasps, Polistes biglumis and Polistes gallicus

“…While solitary insects cannot care much for brood development after egg deposition if environmental conditions change, social insects have more possibilities 14 , 16 . Vespine wasps and honeybees can use endothermic heat production to stabilize brood temperature, because an insulating nest envelope reduces heat loss 15 , 17 , 18 . The open-combed nests of Polistes wasps, by contrast, not only loose heat immediately to the environment but also gain it fast 16 , 20 , 49 .…”

“…If adults of social insects activate their flight muscles the brood can benefit from the emitted heat (e.g. 15 ). In Polistes paper wasps, however, any active (metabolic) heating effort of the adults would mean much wasted energy because the heat is immediately lost to the surrounding air 14 , 16 – 19 .…”