Flowers are not enough, it seems. For the first time, bees have been discovered farming fungus to provide extra food for their larvae.
Though farming is well known in many social insects, such as ants and termites, bees have always been thought to depend solely on pollen and nectar for sustenance.
But for the Brazilian stingless bee, Scaptotrigona depilis, fungus may mean the difference between life and death.
What’s more, if other bees also depend on fungus for survival, the discovery has serious implications for the use of fungicides in agriculture.
Cristiano Menezes of the Brazilian Agricultural Research Corporation, was studying the bees in the lab and originally mistook the white Monascus fungus growing in their hive for contamination.
Integral to the hive
But when he found it in all 30 hives he looked at, he began to suspect it was there for a reason, especially since it was growing inside brood cells – the structures that social bees build to house their growing larvae.
He and his team discovered that the fungus is a key part of the hive. It permeates the cerumen, a material made of wax and resin that the bees use as building material. After the bees have deposited regurgitated food for the larvae inside the cells, and laid an egg, the fungus starts growing.
Once the egg hatches, the larva feeds on the fungus, and it turns out this food is absolutely crucial. When the team tried to grow the bees in the lab without the fungus, the survival rate of the larvae dropped dramatically – from 72 per cent to just 8 per cent.
The survival difference may be either due to some nutrients provided by the fungus, or due to the fungus protecting the regurgitated food from spoiling, they say.
When bees leave to start a new colony, they take some of the cerumen with them to build the new hive structures, so their fungal farm comes too.
“It is clear that the fungus profits from dispersal with the bees, both to new colonies and within the nest, and is offered a protected environment,” says Duur Aanen of Wageningen University in the Netherlands.
Menezes calls it “proto-farming”, as the bees don’t seem to actively tend to the fungus. But they do “plant” it, provide stable growing conditions and food, harvest the crop and depend on it – all features of farming seen in other social insects, such as ants and termites. One ant species even farms animals for meat. And some fungi are farmers themselves, of bacteria.
“It is an exciting example of the complex connections between insects and microscopic life,” says Cameron Currie of the University of Wisconsin. “And it illustrates the important roles for beneficial symbionts in insects.”
Both Menezes and Currie think there are more farming bees to be found. “Given the substantial diversity of bees, many of which are poorly studied, it is likely that other bees engage in similar associations,” Currie says.
This raises concern about the use of fungicides, which while not directly harmful to bees, may be affecting them by killing off their symbiotic fungi, Menezes’s team concludes.