As fall rolls around, you may hear tell of beekeepers feeding over-ripe bananas to their bees. Many say that it helps with nutrition and to combat chalk brood. I am very skeptical of this practice and will share the reasons for my skepticism below.
To my knowledge, the only research that exists on this topic was done by Katharina Davitt as the final project for her Master Beekeeper certification. It is not peer-reveiewed science. It is a very well done project, but it's not the same as a primary source study.
A Summary of Her Project
She starts her project by looking at the very limited number of papers previously published about bees eating bananas. These do not look at whole bananas, but at a syrup made from bananas in tropical countries where the fruit is more plentiful and/or affordable than refined sugar. In both of these studies, banana syrup was found to be an adequate substitute for sugar syrup.
Next, she compares the nutritional profile of bananas to the recommended nutritional profile for pollen patties. They measure up in minerals, but bananas lack when it comes to vitamins and amino acids.
Finally, she addresses the idea that bananas could help with chalk brood based on anecdotal results in Australia. The two theories for why the might possibly help with chalkbrood are:
As the bananas break down, alcohols are produced that kill fungus (this applies to a kind of mold on oranges, NOT specifically to chalkbrood)
The presence of something foreign in the hive stimulates hygienic behaviour in bees.
Why I'm skeptical
There are a few reasons that I will NOT try feeding bananas to my own bees. First is the problem of ash. Banana peels are very high in ash (solids that cannot be digested and become poop; very problematic at times of year when bees cannot take regular cleansing flights). They come in at 16% ash where the recommended maximum level of ash in anything bees eat is 3%.
Next is the alcohols. While this has been suggested as a mechanism for bananas combating chalkbrood, I believe there is more evidence that alcohols (particularly the yeasts involved in making them) are very bad for bees' guts.
If the goal is nutrition, I think that you'd do better to offer sugar syrup and pollen patties to your bees. While feeding bananas might not do any harm, the high levels of ash certainly could be harmful if winter comes on suddenly and your bees can't leave the hive to cleanse all those solids.
And a fun and nerdy aside for those who might argue that their bees just really seem to like eating bananas: the peels are full of dopamine and bees are dopamine driven just like we are! (But I think we can all agree that not everything we do in pursuit of dopamine is actually good for us!).