Insulation vs Ventilation?
The long-running debate among beekeepers about whether insulation or ventilation is a more important consideration when preparing hives for winter may be nearing an end, judging by this pre-print 
Those in favour of insulation claim that bees need to keep warm enough to access food stores around the hive, and to raise brood successfully in the late winter. Those in favour of ventilation claim that without good airflow, hives get damp inside, promoting the growth of fungal diseases, such as nosema.
This study finds that, though honey bees keep their hives at a fairly constant temperature, they keep the humidity even more constant, suggesting humidity is the more important factor.
 Iris Eouzan, Lionel Garnery, M. Alice Pinto, Damien Delalande, Catia Neves, Francis Fabre, Jérôme Lesobre, Sylvie Houte, Andone Estonba, Iratxe Montes, Télesphore Sime-Ngando, David Biron
Hygroregulation, a key ability for eusocial insects: Native Western European bees as a case study
A pre-print is a paper that’s has not yet been published in a journal, and may never be. It will not have been peer-reviewed and may be subject to substantial correction or even withdrawal.
Update: The following related article was published in February 2019.
Eouzan I, Garnery L, Pinto MA, Delalande D, Neves CJ, Fabre F, et al. (2019) Hygroregulation, a key ability for eusocial insects: Native Western European honeybees as a case study. PLoS ONE 14(2): e0200048. https://doi.org/10.1371/journal.pone.0200048