Stingless Bees 'Farm' Fungus to Feed Young

A type of Brazilian stingless bee, Scaptotrigona depilis depends on a fungus to survive. Cristiano Menezes et al

Humans were not the first animal to farm. Leafcutter ants, for example, go to great lengths to raise the fungal gardens upon which they feed. So do certain termites. And now, it appears that a Brazilian bee also cultivates and relies upon a fungus to survive.

Scaptotrigona depilis, a type of stingless bee, has a lovely ritual for rearing young. First, the worker bees regurgitate a semi-liquid food mass into a wax chamber. Then, the queen lays an egg atop this precious gunk. Next, the nurse bee closes up the chamber, which remains sealed until the egg develops into a larva and then into an adult that emerges.

Upon doing research on this species in the lab, scientists Cristiano Menezes and colleagues at the Brazilian Agricultural Research Corporation noticed a fungal growth within these chambers. This was unexpected. Was this contamination? What was going on? Menezes conducted a series of experiments to show that not only do the larvae eat this fungus, but they cannot live without it, he explains. This is the first time that a bee has been shown to cultivate and establish a symbiotic relationship with a fungus, says Mônica Tallarico Pupo, a researcher at the University of Sao Paulo who wasn't involved in this work.

In a study published today in the journal Current Biology, the team has shown that after the nurse bees lovingly vomit into the birth chamber, the fungus begins to grow out of the walls, which are made out of cerumen, a mixture of wax and plant resins. By the time the egg hatches three days later, there are plentiful fungal filaments to feed upon. The larva eats the fungus as it develops over the course of several days.

This fungi-bee relationship appears to be mutually beneficial, Menezes says; the bees shelter the fungus and give it a safe place to live. The fungus begins to grow in the presence of the larval food, suggesting that it likes whatever is in there, he adds. And the fungus provides food to the bees, and perhaps also creates antimicrobial chemicals that help keep them healthy, he adds.

The chambers are made of cerumen, a mixture of wax and resins, in which stingless bee larvae feed on a symbiotic fungus. Cristiano Menezes et al

Menezes says that this fungal mutualism makes the bees more vulnerable to fungicides, which are "generally applied during blooming periods and in large doses. Since fungicides do not affect adult bees directly, no one is worried about killing bees with fungicides," he says. "However, these fungicides are frequently found in both nectar and pollen of honeybees and may affect symbiotic microorganisms of the colonies, which play important functions for nutrition and protection of the colony."

When bees make new nests, they take with them pieces of the old cerumen—impregnated with dormant fungi. This way, the fungus is passed on. In all other fungi-cultivating insects, the queens take the microbes with them to new homes. But here, it is the workers' doing. "This is unique among all insects which cultivate fungus," Menezes says.

In one experiment, Menezes fed one group of larvae fungi-enriched food and another group fungi-free food. While 76 percent of the former survived, only 8 percent of the latter made it.

A Scaptotrigona depilis worker toils inside a flower. Cristiano Menezes et al

The researchers sequenced the genes of the fungus, and placed it in the genus Monascus. Several species of this genus of fungus have been used for centuries by humans, especially in eastern Asia, as a food coloring, to ferment cheese and fish and for medicinal purposes, says Petra Patakova, a researcher at the University of Chemistry and Technology Prague who wasn't involved in the paper.

Stingless bees, as their name implies, lack a stinger and are generally less aggressive than more familiar honeybees and bumblebees. The production of honey and other products from stingless bees is called meliponiculture, which comes from Meliponini, their taxonomic name (while the honey cultivation of honeybees is called apiculture). Meliponiculture is widespread in the tropics and growing in prevalence and popularity. That's because these insects fertilize many more species of flowers and live in a wider variety of habitats than honeybees.

Moreover, there are many uses for the widely varied types of honey these bees produce. Honey produced by a West African species, for example, is more effective at treating eye infections than a synthetic antibiotic, according to a 2012 study in the Journal of Experimental Pharmacology.