Do honeybees, Apis mellifera scutellata, regulate humidity in their nest?

Abstract

Honeybees are highly efficient at regulating the biophysical parameters of their hive according to colony needs. Thermoregulation has been the most extensively studied aspect of nest homeostasis. In contrast, little is known about how humidity is regulated in beehives, if at all. Although high humidity is necessary for brood development, regulation of this parameter by honeybee workers has not yet been demonstrated. In the past, humidity was measured too crudely for a regulation mechanism to be identified. We reassess this issue, using miniaturised data loggers that allow humidity measurements in natural situations and at several places in the nest. We present evidence that workers influence humidity in the hive. However, there are constraints on potential regulation mechanisms because humidity optima may vary in different locations of the nest. Humidity could also depend on variable external factors, such as water availability, which further impair the regulation. Moreover, there are trade-offs with the regulation of temperature and respiratory gas exchanges that can disrupt the establishment of optimal humidity levels. As a result, we argue that workers can only adjust humidity within sub-optimal limits.

Hygropreference and brood care in the honeybee (Apis mellifera)

“…The results of this study suggest that a humidity of approximately 75% RH (higher than 55% and lower than 90% RH) is an optimal value in the brood nest. This value is higher than that measured by Human et al (2006) in hives in the field during the dry South African winter, but comparable to other measurements in field colonies conducted simultaneously with the present study, in spring and summer (Ellis MB, unpublished data). This discrepancy could thus be due to different measuring conditions (laboratory versus field) or to seasonal or intercolonial variation in humidity regulation or preference.…”

“…royal jelly, respiration of nest inhabitants, nectar) and saturate the nest's atmosphere with water vapour. The fact that such high humidity is not measured in hives (Human et al, 2006) and that a preference for a lower humidity level was detected in our study suggests that it could be adaptive for honeybees to actively decrease humidity in the nest to a preferred level. Avoidance of high humidities could contribute to an increase in adult longevity and decreased microbial development.…”

“…This is in spite of the fact that these groups might have performed different tasks prior to their placement in the experimental setup. It is possible that, based on differences in humidity of the different nest regions (Human et al, 2006) where workers are active, individuals would show different hygropreferences. Workers caring for brood (6-day-old) and brood cell cleaners (3-day-old) could have a preference for higher humidity compared to workers active in the drier region of nectar stores (Human et al, 2006).…”

“…It is possible that, based on differences in humidity of the different nest regions (Human et al, 2006) where workers are active, individuals would show different hygropreferences. Workers caring for brood (6-day-old) and brood cell cleaners (3-day-old) could have a preference for higher humidity compared to workers active in the drier region of nectar stores (Human et al, 2006). In addition, we detected no difference in the behaviour of workers that were exposed to eggs or larvae, suggesting a similar sensitivity of these brood types to desiccation and no preference of 6-day-old workers for tending either of them.…”

“…The occurrence of this bias can be excluded if workers distribute themselves randomly between chambers with identical humidity. We therefore measured the distribution of workers in a setup where a humidity of 55% RH (which frequently occurs in honeybee nests, Human et al, 2006) was maintained in all chambers using a Mg(NO 3 ) 2 solution (N = 5 colonies).…”