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Wine-delivering wasps

By John Upton

Yeast is a salubrious if invisible vintner, and scientists have discovered an important role that wasps have played in its spread and evolution in vineyards around the world.

Species of the single-celled fungal genus Saccharomyces feast on grape sugar and break it down to create alcohol molecules.

(That’s not all, of course. By shearing carbon and oxygen atoms away from carbohydrates in decomposing barley, the yeast produces booze while shaking loose pockets of carbon dioxide that manifest as bubbles in a freshly cracked beer. When the yeast produces those bubbles inside dough, the result is bread’s delightfully airy texture. Other genera of yeast fashion hard liquor, chocolate, soy sauce and scores of life’s other routine gastronomic indulgences from otherwise questionably-edible ingredients.)

Most modern wine, beer and bread makers purchase Saccharomyces and pour the yeast directly into their concoctions. But wine, beer and bread emerged as staples long before anybody understood their microbiotic secrets — in various continents and countless cultures over at least the last 9,000 years. Many of these early vintners, brewers and bakers relied on nature to deposit the mystical ingredient into their potions.

Where did this yeast come from, if not from a packet? How could nature be so dependably relied upon to provide this ingredient, apparently from thin air?

Illustrated by Perry Shirley
Illustrated by Perry Shirley

The answer rests in fungi’s remarkable ability to flood the environment with its own microscopic spores and then to lay low, requiring little to no sustenance, until it settles on food that allows it to quickly flourish.

A team of French and Italian scientists reported in 2012 in Proceedings of the National Academy of Sciences that vineyard-visiting social wasps in Italy were found to be both vectors and natural reservoirs of S. cerevisiae. The group, which expects to publish follow-up research in the same journal shortly, concluded that the wasps served as a “key environmental niche for the evolution” of a yeast used for winemaking — a yeast that cannot spread through the air unaided.

The group found the yeast inside the guts and nests of wasps, suggesting that the insects inadvertently gather the yeast while foraging in vineyards for food. Hibernating queens provide the yeast with a warm and safe winter home, and then the progenies of the queens help deposit the fungus back onto grapes as the fruit comes into season.

“Our work suggests that wasps could move wine strains and maintain diversity, favoring crosses between strains involved in wine making and wild strains,” Duccio Cavalieri, a microbiology professor at the  University of Florence who was involved with the research.

(A version of this post originally appeared on Wonk on the Wildlife in 2012.)

Surviving Fires, Global Warming — With Naps

The unprecedented Black Saturday bushfires in the countryside surrounding Melbourne in 2009 left 1 million acres of Australian landscape charred. Squeaked mousey marsupial after losing its insect hunting grounds: “Yawn.”

Wildfire-adapted wildlife has to cope with more inferno-related threats than just the flames.

The scorched earth left behind by wildfire can be bereft of the plants and insects that are used for food by many small animals. As they move through the black landscape, these animals can lose their camouflage and succumb to predators.

To survive these tough times, some antechinuses — marsupial mice in Australia and New Guinea — amplify their siesta-style torpor, taking longer power naps every day.

That reduces their daily energy needs, allowing them to get by on less while the forest recovers around them.

“There’s a perception that bushfire affects animals through the direct effects of fire killing individuals,” said Australian National University researcher Sam Banks.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

“Certainly, this happens,” Banks said. “But it seems to be the availability of crucial resources in the post-fire environment that determines whether animal populations persist.”

In 2009, Banks led a group of scientists that aimed to use the aftermath of the fires as a laboratory to investigate how two species of small marsupials survive and recolonize after bushfire.

The team found that agile antechinuses were more than twice as likely, compared with bush rats, to continue inhabiting a scorched habitat after a fire.

The antechinuses — which eat insects and, despite their outward resemblance, are not rodents — were 30 percent as likely to inhabit a burned patch of land compared with an unburned one. The bush rats (they are native rodents) were 12 percent as likely.

“It always seemed to me slightly unusual that such a small mammal with high energetic requirements would persist in burnt habitat with — presumably — reduced food availability,” Banks said.

An agile antechinus. Photo by Michael Sale/Flickr
An agile antechinus. Photo by Michael Sale/Flickr

New research suggests that the use of torpor could explain the antechinuses’ reluctance to flee post-fire landscapes.

“It’s interesting to see that they might have some physiological responses that would enable them to cope with tough periods,” Banks said, after reading the new paper, which was published in the journal OIKOS by a team of scientists from Australia’s University of New England.

“For antechinus, they shelter in hollow trees, all but the most decayed of which remain standing after fire,” Banks said. “I guess the torpor response helps them deal with the lack of food.”

The University of New England paper tracked brown antechinuses, which closely resemble agile antechinuses, in and near a 1,000-acre prescribed fire in a national park in southeastern Australia. The researchers focused on females, in which torpor is more pronounced.

One of the five females being studied in the burned area took shelter from the fire beneath rocks, where it was killed by the flames.

The other four took shelter in trees, where they survived. Before the fire, they had spent about half their time in states of torpor, in which metabolism slows down and energy is conserved. The same was also true for a control population studied.

After the fire, the four female survivors spent most of their time in torpor. The average power nap rose in length to an average of three to five hours — up from between one and three hours.

One female clocked up more than ten hours of nonstop torpor after the fire. That doubled the group’s pre-fire torpor record.

These marsupials are pulling a trick known as heterothermy.

A heterothermic mammal or bird can display the characteristics of a warm-blooded endotherm, churning through energy as it ferrets about for food and mates. But when it needs to slow its demand for energy, it can hibernate, or enter a briefer form of daily hibernation known as torpor, displaying characteristics of a cold-blooded ectotherm — such as a snake.

The list of heterotrophs is long — check out this table from a Current Biology article by University of New England professor Fritz Geiser. Geiser also led the antechinus torpor study published in OIKOS.

Current Biology
Current Biology

Some scientists have argued that heterothermy helped some mammals survive the mass extinction that killed the dinosaurs.

As earth’s biosphere plunders into the anthropocene, and as greenhouse gas pollution drives longer and harsher wildfire seasons, these marsupials’ heterothermy may give them a fire-resistant evolutionary upper hand.

It is “likely,” Geiser wrote in his 2013 Current Biology essay, that “opportunistic heterotherms may be better equipped” than other species to cope with “anthropogenic influences such as habitat destruction, introduced species, novel pathogens and specifically global warming.”

That, he wrote, is because these animals have “highly flexible” energy needs, can limit foraging and avoid predators.

Fairy wasps unleashed to protect Eucalypts

By John Upton

Eucalyptus trees are the scraggly kings of Australian landscapes, growing hard and fast, resilient to fire and sundry other stresses. After their crowned heads were plucked from native wildlands and thrust into monoculture plantations in continents far afield, though, pests began sucking the antipodean puissance out of the botanical emperors.

Cue scientific tinkling and hopes for a tiny-winged salvation.

A healthy Eucalyptus plantation in Hawaii. Photo by Forest and Kim Starr.
A healthy Eucalyptus plantation in Hawaii. Photo by Forest and Kim Starr.

Natural forests and other ecosystems are being cleared the world over to make space for Eucalyptus plantations. They sprawl over millions of acres, from the American Southeast to Africa to New Zealand.

The trees are largely being grown to be pulped for paper and, more recently, to be burned to produce energy. Sometimes they’re just planted along paths and roads and as forests because they’re easy to grow, and they look nice.

Amid this upheaval, a biological chink has been gouged from the trees’ armors of hitherto resilience. Across the globe, Eucalypts in plantations and neighborhoods alike are being attacked by tiny sap-sucking bugs.

The culprits are called bronze bugs — because their victims’ hues change from green to bronze as their leaves dry out. As the sap is sucked from the trees, their growth is crippled. The heaviest of attacks can leave the trees dead.

Bronze bugs
Bronze bugs on a Eucalyptus leaf. Photo by Simon Lawson.

To protect hulking gum tree plantations from bronze bugs, scientists are starting to release even tinier critters. Their newest weapon is a species so small that it lays its eggs inside the eggs of the marauding pests, which hatch to feast on the meat of an egg that was laid for another, killing the unborn.

Eucalyptus trees, the bronze bugs that steal their sap, and the fairy wasps that hijack the bronze bugs’ eggs are all Australian natives. But until the turn of the century, few people had given the bronze bugs any thought. That’s when they started attacking trees in Sydney — possibly infesting tree species that had been transplanted outside their native ranges.

“There were very few records of it until it started outbreaking in Sydney in the early 2000s,” said Simon Lawson, a University of the Sunshine Coast entomologist who studies Eucalyptus pests.

From Sydney, the bronze bugs spread, hitchhiking with world trade to South America and South Africa, where the invasive populations made themselves at home amid their native prey. More recently, they’ve have been spreading through Europe and the Middle East. They’re also in New Zealand.

A fairy fly
A fairy fly. Illustrated by Perry Shirley.

The bronze bug outbreaks have coincided with a substantial rise since the 1990s in the spread of exotic pests in general — and, more recently, with a rise in the spread of Eucalyptus pests.

“Just in the last ten to 15 years or so, there’s been a real increase in the number of Australian-origin Eucalyptus insects that have been moving around the world into Eucalyptus plantations,” Lawson said.

To try to relieve the problem, Lawson and other researchers across the planet are turning to the pests’ natural predators. The main predator tested in laboratories and dispatched in the wild so far has been Cleruchoides noackae. C. noackae are from a family of wasp and ant relatives called fairyflies — or fairy wasps. As the name suggests, the family includes some of the tiniest insects ever discovered.

C. noackae
C. noackae. Photo by Samantha Bush, University of Pretoria.

Fairy wasps are often used as biological controls — as sentient insecticides.  They’re all parasitoids. That’s similar to a parasite, but dialed to a different equilibrium: parasites generally let their hosts live; parasitoids do not.

Following quarantine and tests that convinced them C. noackae was safe for native bugs, Brazilian agriculture officials released swarms of  them in the state of Minas Gerais in 2011. Two years later, field research found that about half the bronze bug eggs in local Eucalyptus plantations had been parasitized by the fairy wasps.

The results, which will be detailed in an upcoming scientific paper that’s still being finalized by Brazilian agriculture officials, are “quite a bit better than what we’ve seen in the native populations in Sydney that they’re derived from,” Lawson said.

Similar releases are planned or already underway in other South American countries and in South Africa.

Cracking the bronze bug problem, which was set off when Eucalypts were introduced to exotic environments, might mean doubling down on the number of species that are introduced to patch the problem over.

Ongoing research to identify alternative biological control agents, such as other species of fairy wasps, will also be critical for controlling the pests, Lawson said. “You’re better off having more than one agent.”

Bronze bug eggs on an infested leaf. Photo by Simon Lawson.
Bronze bug eggs on an infested leaf. Photo by Simon Lawson.