This 2016 video says about itself:
Bee Hunting: Finding a Wild Colony of Honey Bees
One method of locating a colony of wild bees is called beelining. In this video, we will join Prof. Tom Seeley as he tries to locate a wild colony of bees. He catches bees foraging on goldenrod and aster, feeds them concentrated sugar solution and determines the direction that they fly as they return to their colony. By painting identifying marks on some bees, he is able to measure their round trip time to get an estimate of the distance to the colony. With direction and distance established, he moves closer. Then, watching the bees, sees that they are living in a dead tree.
From the University of Würzburg in Germany:
Tree cavities for wild honeybees
December 11, 2019
Summary: The forests in Europe provide habitat for around 80,000 colonies of wild honeybees. That is why more attention should be paid to preserving the nesting sites for these threatened insects, according to researchers.
Wild populations of the western honeybee Apis mellifera were widely assumed as extinct in Europe. “However, recent fieldwork studies reveal that wild honeybees still exist in forests: Their colonies mainly nest in tree cavities,” says Dr. Fabrice Requier from the Biocenter of Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany.
So far, wild honeybees have only been observed in northern Poland and Germany (the Hainich forest and the Biosphere Reserve Swabian Alb). Research groups from Germany, France, Italy, and the Czech Republic, led by the JMU, have now asked themselves where there might be other suitable habitats in Europe.
The four teams analysed the tree cavity densities of 106 forest areas across Europe and inferred for the first time an expected population size of estimated 80,000 wild honeybee colonies in European forests. This is reported in the journal Conservation Letters.
Where there are hotspots for wild honeybees
The researchers have also identified the hotspots where wild honeybees find a particularly large number of nesting sites. On the one hand, these are unmanaged forests, for example in national park areas. Surprisingly, hotspots also include forests in which the nesting trees exist not so densely, such as the extensive coniferous forests in Sweden and Finland.
The scientists’ conclusion: it is worthwhile to include the conservation of trees with cavities in forest management, even in commercial forests. This is entirely in line with the EU strategy to halt the decline of honeybees and other pollinators.