Beetles Bring Yeast to Bamboo for Babies

Humans are not alone when it comes to farming. We are not even alone when it comes to growing fungi. There is a long history of fungal agriculture in social insects. Ant and termites often even go so far as to have what could basically be considered proper gardens of fungal blooms; getting them into the right growth medium, tending to their needs, even defending them from invaders. It is all quite industrial, but that is the kind of thing we come to expect from ants.

Now a Japanese study is demonstrating that at least one less industrialized, even non-social, beetle has tapped into the joys of harvesting fungi.

Fungal Farming in a Non-Social Beetle

This study focuses on a species of lizard beetle, Doubledaya bucculenta, that lives in Japan and lays eggs in dead bamboo. Collecting specimens of D. bucculenta at Kawaminami, Miyazaki Prefecture, Japan The team found that there was a white coating in internode cavities that were used to contain larvae, as well as on the larvae themselves.

D. bucculenta, its host bamboo, and W. anomalus

Analyzation of this growth consistently showed the saccharomycete yeast Wickerhamommyces anomalus present in the shoots used by D. bucculenta. Looking at bamboo not used for the incubation of young this same fungus was absent. When you find a fungus repeatedly, and only, growing in the presence of developing larvae, you might want to wonder if something is up.

By gathering and dissecting both adult males and females of D. bucculenta an interesting structure was catalogued. The females all displayed a yellowish exoskeletal pocket on the eight abdominal segment, right next to the ovipositor, and guess what they found there. Correct! They found small yeast particles that when isolated and sequenced turned up with the identical DNA of W. anomalus that had already been collected.

So, is this yeast a parasite, perhaps feeding off the larvae of the beetle or the insides of the bamboo? Or, could it be that the beetle was engaging in some low level farming, putting a crop into its young's room for later. W. anomalus is known to be saprophytic so it could potentially be using the beetle as a transport to get on the inside of freshly dead bamboo, but that would hardly be cause for the storage pocket on the female beetle. If however, the beetle were harvesting the fungus and seeding the bamboo chamber with it when she deposited her egg, how would that affect the larva?

To test this, the researchers grew some beetle larvae under a variety of scenarios. When inoculated with W. anomalus the larvae grew normally into adulthood, however when grown on sterile media or in autoclaved bamboo they stopped growing at the second instar. Furthermore after this if W. anomalus was added the larvae returned to its normal growth and development.

So, it appears that D. bucculenta does indeed harvest and transplant W. anomalus into the incubation chamber of its young. This interesting mutualistic relationship has led the beetle to becoming obligately dependent on the very fungus it developed a structure to harvest.

In the end finding this fungal farming tactic in a non-social insect could help shed light on how some of the higher levels of mutualistic cultivation developed. And in the end, the researchers think this could shed light even on how agriculture developed as a whole.

Awesome researchers:
Wataru Toki, Masahiko Tanashi, Katsumi Togashi, & Takema Fukatsu (2012). Fungal Farming in a Non-Social Beetle PLoS One DOI: 10.1371/journal.pone.0041893