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.
Highlights
The honeybee (Apis mellifera) displays advanced regulation of the nest climate, in summer as well as in winter (Hess 1926; Himmer 1932; Simpson 1961; Kronenberg and Heller 1982; Southwick 1983, 1985; Seeley 1995; Stabentheiner et al 2003a)
While observation hives are well suited to investigate the mechanisms of temperature homeostasis (Bujok et al 2002; Kleinhenz et al 2003; Stabentheiner et al 2010), they have a considerably higher heat loss than standard commercial bee hives or naturally nesting colonies (Mitchell 2016, 2019)
Endothermic bees were only identifiable by detailed evaluation of the thermograms
Summary
The honeybee (Apis mellifera) displays advanced regulation of the nest climate, in summer as well as in winter (Hess 1926; Himmer 1932; Simpson 1961; Kronenberg and Heller 1982; Southwick 1983, 1985; Seeley 1995; Stabentheiner et al 2003a). While observation hives are well suited to investigate the mechanisms of temperature homeostasis (Bujok et al 2002; Kleinhenz et al 2003; Stabentheiner et al 2010), they have a considerably higher heat loss than standard commercial bee hives or naturally nesting colonies (Mitchell 2016, 2019). In a colony of standard size and type, the rate and degree of endothermy can be expected to be equivalent to natural conditions. Such measurements have been carried out in winter clusters (Stabentheiner et al 2003a) but are still missing in breeding summer colonies. According to common rules of biological and technical cybernetics, we hypothesised that a breeding colony will have to establish regulatory stability by counteracting heating and cooling mechanisms
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