Master Naturalists: Wasps play role in wine making

Numerous species of polistes wasps live on most continents. They are all paper wasps, given their nest-building habit shown here. In spring, they hunt small insects that they partially digest and feed to their larvae. They also have a sweet tooth, enjoying nectar and ripe fruit like peaches, plums, watermelons and grapes. European species transfer yeast spores to grapes, giving them a dusty coat on their skins at maturity. This is the start of fermentation in making wines.

Face it, Paul is a bug guy. He is an Agrilife entomology specialist who likes six-legged critters, even bees and wasps. This interest came after some interesting and painful experiences as a youth.

What do wasps have to do with his other interests, wine-making and baking? Quite a bit.



Evolutionary biology of wasps, yeast

Recently, scientists in Europe asked the question: How does yeast get on grapes as they mature? That's an important question. All yeasts for baking, beer and wine-making were domesticated over the last 9,000 years from Saccharomyces cerevisiae, baker's yeasts, found on mature grapes.

Paul assumed, based on wine-making sources, that yeast spores floating around in the air stuck on grapes, found sugar and multiplied.

The researchers at the University of Florence found there's a bit more of a complex process taking place, storing cultures of a vineyard's yeast over the winter and reintroducing the same yeast strains to the vineyard just when the grapes ripen, year after year. They found that two species of social wasps, hornets and paper wasps, Vespa crabro and Polistes spp, acted as vectors and receptacles for overwintering and inoculating yeast in vineyards.



How it works

Wasps love sugar and ripe grapes have lots of it. They're pests during grape harvesting in Paul's cousin's California vineyard. With uniquely adapted mouth parts that let them pierce the thick skins of a grape, they feed on the grape juice and in the process both inject yeast from their gut and consume sugars to feed their own yeast colony in their gut.

Where did the yeast come from? Wasps are annuals; they die in winter. Except that a fertile queen burrows into warm material and hibernates until spring. She awakens to start a new colony.

After the queen's eggs hatch, she feeds her larvae with a mash of partially digested food she has eaten since awakening. Researchers found queens' guts also contained large amounts of active, overwintered yeast spores, which are part of the larvae's food.

When offspring mature, they are full of yeast, ready to repeat the cycle of pollination of grapes with other bees and wasps, and then the reintroduction and perpetuation of yeast on their vineyard grapes.



Unique yeast strains

The field research by the Florence researchers has some interesting implications. Not surprisingly to Paul, the maximum number of wasps in a colony happens to coincide with the peak sugar content in vineyards (harvest time), lots of food, lots of wasps, lots of rapidly-multiplying yeast to pass on - a symbiotic relationship where everyone wins.

Based on DNA sequencing, they found that genetically unique strains of yeast were passed on to the same vineyards.

What makes Champagne wines different from a Sangiovese (used to make Italian Chianti) may very well be the result of the unique yeast they harbor in overwintering wasps.

We can further appreciate the unique ways that nature adapts and evolves, benefiting mankind as a whole.

Without these wasps, Edward FitzGerald's Rubaiyat of Omar Khayyam quote, "A Jug of Wine, a Loaf of Bread - and Thou, Beside me singing in the Wilderness .", might be meaningless.

Sources: "Role of social wasps in Saccharomyces cerevisiae ecology and evolution", Irene Stefaninia, Leonardo Dapportob, Jean-Luc Legras, et. al., PNAS Early Edition, pnas.org/cgi/doi/10.1073/pnas.1208362109; Genetic sequence referred to here have been deposited in the Gen-Bank database (accession no. JQ946429-JQ946518); "Rubaiyat of Omar Khayyam", Third Edition (1947), Edward FitzGerald, therubaiyat.com/fitzindex.htm

Paul and Mary Meredith are master naturalists. Contact them at paulmary0211@sbcglobal.net.