Category Archives: Defense

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.

Bambi should have been shot and killed, science says

By John Upton

Is it better to kill an orphaned fawn, or is it better to leave it alive, left to try to survive alone in a menacing world?

That unpalatable question is not a hypothetical one in Scotland, where some 60,000 red deer are culled every year — part of an effort to keep populations down to protect crops and woodlands from the hungry grazers.

And Scottish policy is clear on what the answer should be after a hunter orphans a fawn: Kill the baby.

“Shoot both female and juvenile where-ever possible,” the guidelines state. “Where possible target calves first and maintain vigilance for orphaned calves. ”

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

Josephine Pemberton, a professor at the Institute of Evolutionary Biology, University of Edinburgh, wanted to know whether that policy was scientifically wise. Using funding from the U.K. National Environmental Research Council, Pemberton and five other scientists analyzed data from censuses of a red deer population on Scotland’s Isle of Rum dating back to the 1970s.

What they found was that depriving a deer of its mother’s care and protection before its second birthday triggered resounding impacts. Orphaned males and females were more likely to grow haggard and die young. Males were hit particularly hard — and male orphans had trouble growing antlers as they matured, reducing their chances of winning mates and reproducing. As for female fecundity? “Although we failed to find evidence that female orphans paid a reproductive cost,” the scientists wrote in their paper, which was published in August in the journal Behavioral Ecology and Sociobiology, “we cannot discount an effect on female physical condition.”

Pemberton said the results show that young deer should be killed if they are orphaned by a hunter — even if they are old enough to not seem helpless.

“If anything, our results suggest that if a young animal is still going around with its mother in its second year — and they often do — you should try and shoot it then, too,” Pemberton said.

But that’s easier said than done. And not just because shooting a fawn must surely be a heartrending task for even a hardened stalker.

“Although culling calves with their mothers is in the best practice guidance, stalking is a tough job done largely alone,” Pemberton said. “Stalkers are often under pressure to shoot a lot of hinds. Shooting the pair takes time and effort and we know they don’t always manage to do it.”

These chicks puke at predators

By John Upton

When Eurasian rollers forage for insect prey for their young, they’re not just on a quest for nourishing fat and protein. They’re fossicking through an ecological armory for chemical weapons.

Some plants produce toxins to deter herbivores. Some insects that eat those plants use those plant toxins for their own defense. Eurasian roller chicks use the plant toxins from those insects to produce a pungent orange liquid — an unsavory concoction that scientists have concluded is used as a defense against predators.

A team of Spanish researchers found that Eurasian roller nestlings vomited when they picked them up, but not when they approached the young birds, talked to them or gently prodded them. “This fact suggests that the vomit might be produced in response to some kind of predators that actively grasp and move prey during the predation event such as snakes, rats and mustelids, which are common predators of hole-nesting species as rollers,” the scientists wrote in a paper published in the journal PLOS ONE.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

The researchers collected the puke and smeared some of it on pieces of chicken, which they offered (with the smeared side hidden) to 25 dogs alongside a similar chunk of poultry smeared only with water. Some of the mutts strangely showed no appetite for chicken whatsoever. But 18 of the 20 dogs with a hankering for hen opted first for the untreated meat, indicating that the smell is off-putting for a predator. Most of those 18 dogs subsequently wolfed down the vomit-smeared chicken, but six of them left it entirely alone.

“One could wonder about the nestling advantage of this defence,” the scientists wrote. “Kin selection is a possible answer to that question because a predator that finds the first nestling of a brood of five to be distasteful may leave alive the others.”

From where do the chicks get the hydroxybenzoic and hydroxycinnamic acids, phenolic acids and psoralen needed to produce their unpalatable puke?

The scientists matched these compounds to toxins produced by plants to deter animals from feeding on them. Many insects have developed an immunity to such toxins, and some use the plants’ toxins to defend themselves. That’s the case for many of the grasshoppers upon which the rollers prey, and the scientists believe that the chicks are, in turn, purloining the poisons from the grasshoppers to defend themselves.

But that’s not all — the scientists think that the parent birds might also be hunting for more-poisonous insects, such as centipedes, that most other birds would never touch.

“Grasshoppers are the main prey that rollers hunt to feed their nestlings,” they wrote. “Furthermore, rollers feed their offspring with a large share of poisonous arthropods that are avoided by most of the other sympatric insectivorous birds. This suggests that rollers are resistant to these toxic substances and could have the ability to sequester chemicals from their protected prey to defend themselves.”

An adult Eurasian roller.
An adult Eurasian roller in Kazakhstan. Photo by Ken and Nyetta.

How birds avoid cuckoos

By John Upton

One of nature’s more ridiculous sights is that of a pair of adult birds rearing an oversized cuckoo chick.

Cuckoos are members of a large family of birds, some of which have done away with chick rearing, instead depositing their eggs in the nests of other species. This is called brood parasitism.

The parasitized birds rear the cuckoo chick as if it were their own, even as it grows to dwarf them in size — and as it pushes any other chicks from the nest to certain death.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

(Ever noticed a dead chick beneath a tree and wondered how it fell out? Next time look up for a nest, and wonder whether a cuckoo is being raised therein.)

It seems that the the parental compulsion to raise young is so strong that the parasitized birds remain blind to the possibility that the brood contains none of their own DNA.

While many bird species remain oblivious to what would seem to be obvious signs that they are raising an unrelated chick, selection pressure has of course led to the evolution of some defenses against brood parasites.

Scientists compared defensive strategies developed by barn swallows living in China with those in Europe and found that they developed different defenses.

In Europe, martins and barn swallows, which seem to be better than some similar species at avoiding cuckoos, prefer to build their nests indoors. That’s where cuckoos are less likely to strike; they prefer open areas and avoid human habitation.

“Suitable cuckoo hosts breeding close to human habitation enjoy a selective advantage from breeding indoors,” the researchers wrote in a paper published in the journal Behavioral Ecology and Sociobiology. “These findings suggest that birds benefit from association with humans in terms of reduce risk of parasitism.”

The scientists say it’s harder for the barn swallows to build nests indoors in China. There, they have developed an alternative trick that’s largely lacking among their European counterparts: A Chinese barn swallow will often recognize a cuckoo egg. So when a cuckoo egg shows up in its nest, it will toss it over the side.

“These findings suggest that barn swallows in China have gained egg rejection behavior because they cannot avoid parasitism when breeding outdoors.”

Watch a Reed warbler feed a much larger cuckoo chick:

A hungry red tide is a dangerous red tide

By John Upton

When fertilizer or sewage runs into a waterway, or when phosphorous and nitrogen rise up from the ocean depths, algae can converge and feast and mushroom on the buffet of growth-inducing nutrients.

But scientists have discovered that starving a poisonous red tide of its nutrient supply can trigger a very dangerous and counterintuitive response.

Red tides are freaky types of algae blooms. They often occur in the ocean or in salty bays, and they frequently produce poisons. Scientists prefer the term “harmful algal bloom,” since a red tide isn’t always red and it is most certainly not a tide.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

The most common type of algae in Gulf of Mexico red tides is a dinoflagellate called Karenia brevis. The neurotoxin produced by these single-celled creatures help protect them from predation: Would-be hunters can die if they take a mouthful. But as the red tides break down, the poison escapes from the plankton cells and it can drift through the marine environment, poisoning it. The toxin can even spray into the air, aerosolized by crashing waves, where it can get into lungs and trigger serious ailments in people and other animals. The Floridian West Coast is often the worst affected.

Concentrations of the poison in each of the algae cells varies widely — from a mild 1 picogram per cell to a treacherous 68 picograms per cell. Needless to say, figuring out what causes a bloom to be especially poisonous would be valuable for public health officials.

Since Karenia brevis uses nutrients to grow, one may assume that starving them of phosphorous and nitrogen, such as by preventing fertilizer or sewage runoff into the Gulf, would protect the environment from their poisons.

But that’s only true up to a point. If you can keep nutrients out of the water, a bloom will not materialize, so there will be no danger of the waterway being poisoned by it. But if the nutrient supplies suddenly dry up, an existing bloom will switch into a defensive mode, stop growing and become very toxic.

The ecological theory to describe this response comes to us from botany. It is called the carbon:nutrient balance hypothesis.

North Carolina scientists grew samples of the dinoflagellate in water taken from the Gulf in a laboratory. Some samples were fed plenty of phosphorous, but others received very little. The scientists found that K. brevis strains living with limited phosphorous supplies produced 2.3 to 7.3 times more poison than did those that had plenty of phosphorous available.

“Because PbTxs [K. brevis brevetoxins] are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth,” the scientists wrote in their paper, published last month in PLoS ONE.

The algae samples living without much phosphorous put their carbon to a defensive use, since it couldn’t be used as effectively for growth. The proportion of carbon that each cell used to produce poison as much as doubled when phosphorous was limited.

This is consistent with the carbon:nutrient balance hypothesis. When vegetation has lots of carbon and lots of nutrients available, it invests those building blocks of life into fast growth. But when nutrients, be they phosphorous or nitrogen, are in short supply, the carbon is put to a different use: Defense against predators.

It also helps explain some of the late season bursts in toxicity noticed in the red tides: They become poisonous after they have greedily slurped down the last of the available nutrients.

This research was limited to phosphorous. But previous research uncovered a similar red tide response when nitrogen was limited.

The discovery could help public health managers predict the potency of red tides in the Gulf of Mexico. By measuring the amount of phosphorous in the ecosystem, it could become possible to determine how dangerous the red tides will become.

Cicada wings rip bacteria apart

Illustrated by Perry Shirley

By John Upton

Forget sanitary hand wipes. Scientists have discovered that cicada wings have evolved to kill bacteria without using any chemicals.

The wing are coated with tiny blunt bumps that are so small and plentiful that when a bacterium lands on them, it becomes skewered through multiple parts of its tiny writhing cell wall.

The bacterium doesn’t pop — it is torn open, shredded to pieces by the bumpy wing.

The Australian and Spanish scientists, who published their findings in Biophysical Journal, say the discovery could lead to antibacterial materials “incorporating cicada wing nanopatterns.”

Watch a simulation of a bacterium that was unlucky enough to land on a cicada wing:

Beetles ride global warming up rockies, into vulnerable pines

Illustrated by Perry Shirley.

By John Upton

The grand pine forests that dominate the Rocky Mountains in the American West morph with the montane altitudes. High peaks are home to whitebark pine, a slow growing species that produces energy-rich, pine cone-encased seeds that help grizzly bears grow plump enough to survive hibernation. At lower altitudes are the faster growing lodgepole pines.

The lodgepole pines have long been plagued by occasional infestations of native pine beetles. These dark beetles burrow into tree bark to lay their eggs, which hatch into larvae that feast on the phloem. (Phloem is a tender organ found just beneath the bark that ferries sugars produced by photosynthesizing leaves to other parts of the tree.)

A full blown infestation of phloem-munching beetle larvae is generally fatal. But lodgepole pines have developed a repertoire of defenses against the herbivorous creepy crawlies. They churn out sap and pour it over the invading beetles. They exhale chemicals that repel and kill the adults, prevent eggs from hatching and wreak general havoc with the beetles’ diminutive ecosystems.

Pine trees covered with snow near the top of Polar Peak lift at Fernie Alpine Resort in the Rocky Mountains, British Columbia / Flickr: DCZwick

Whitebark pines have not developed these defenses, at least not to the same extent as their lower-altitude cousins, because they haven’t needed them. The beetles can’t bear the bitter winters that have long swept over the Rocky Mountains’ higher peaks. But now, as climate change sweeps warmer weather over these towering peaks, the whitebarks are in newfound peril.

During occasional warm periods in the past, the beetles would march up the mountains and find a footing in whitebark forests. Then temperatures would return to normal and the pest populations would die off.

“However,” entomologists and ecologists report in the latest edition of Proceedings of the National Academy of Sciences, “recent continuously warm weather has allowed persistent reproduction in this keystone (beetle) species.”

The warming peaks have ushered in an era of beetle infestations that many of the trees have been unable to withstand. More than 100 million acres of mountain forest has been impacted during the past decade. Great forests that used to soak up carbon now lay dead and rotting, releasing their carbon back into the atmosphere, further accelerating the global warming that contributed to their demise.

The Rocky Mountains on Dec. 19, 2012 / Flickr: NASA Goddard Photo and Video

I asked the study’s lead researcher, Ken Raffa, an entomology professor at the University of Wisconsin, Madison, whether he thought the whitepines would be able to evolve defenses against the pine beetles quickly enough to protect themselves from being wiped out. He said he didn’t know: This is something he’s currently investigating, by studying how various tree genotypes are distributed across the mountain landscapes.

But of particular concern to Raffa is the fact that whitepines grow and reproduce very slowly, not producing viable seeds until they reach their 50s, while the beetles can reproduce every year or two, creating an evolutionary handicap.

In addition to marauding beetles, the whitepines also face tremendous threats from white pine blister rust, a ravaging fungus disease. “To be viable,” Raffa said, “whitebark pine would have to escape both.”

African mouse lets predators shred its skin

Acomys kempi, one of two species of African spiny mouse found to shed and regrow chunks of skin / Courtesy: Nature

By John Upton

Lizards, starfish, crickets, snails and earthworms are among the long list of animals that can shed a part of their body to escape a predator. Scientists dub this strategy ‘autotomy.’ Sometimes the lost body part, typically a tail, regrows, although it often regrows into a stunted facsimile of the original organ. A regrown lizard tail, for example, is normally discolored and it’s strengthened with cartilage instead of bone.

That’s pretty weird. But a recent discovery pushed autotomy off the weirdness charts.

For the first time, scientists discovered that a type of mammal sheds its skin to escape predation. Its skin, people! You know, that stuff that clads muscles, organs and blood vessels to protect them from bacteria, viruses and the weather.

Scientists following up on rumors of skin autotomy by African spiny mice found what they were looking for almost as soon as they opened their traps on Kenyan rocky outcroppings.

“Handling both species in the field confirmed that vigorous movement often led to tearing of the skin,” the scientists, from the universities of Florida, Nairobi and Wyoming and the Mpala Research Centre, reported in a recent edition of Nature. “Tearing resulted in large open wounds or skin loss ranging from small pieces to areas approximating 60% of the total dorsal surface area.”

The researchers compared the might taken to tear the specimens’ brittle skin with that taken to shred the elastic skin of a more common species of mouse: It took 77 times more energy to break the skin of the common mouse than that of the spiny one.

This wound quickly healed / Courtesy: Nature

Not only did the rodents readily shed their skin — they hastily grew it back. Five out of six wounds, each 4mm apiece, that were inflicted on the poor creatures by the researchers had completely healed within three days. Compare that with the five to seven days that it takes for a common mouse’s comparable wound to heal.

With additional research into the cellular processes involved with this remarkable healing process, the scientists say the discovery could lead to the development of new ways to heal wounded humans.

Flies pay ultimate price for sex

By John Upton

If you were spending an amorous weekend camping in the woods and you suspected that a bloodthirsty cougar was prowling outside in the dark, would you stay perfectly still in your tent, perhaps clutching a knife? Or would you blithely get busy with your lover, potentially alerting the cat to your presence, knowing full well that copulation could lead to decapitation?

Versions of this unlikely scenario are played out constantly in the wild. But while it has long been hypothesized that mating by insects and other animals increases their risks of predation, firm evidence of such risks has been a little bit hard to come by.

When houseflies mate, they risk being eaten by bats / Flickr: DeeJayTee23

To test one such scenario, German researchers used video cameras to monitor common houseflies in a barn filled with cows and fly-eating Natterer’s bats. When the flies lay on the cowshed’s ceiling or ambled across it, they were virtually immune to predation. The researchers didn’t spot a single bat attack on a walking fly during four years of research. The bats couldn’t find their prey: Their echolocation equipment simply wasn’t sensitive enough.

But once the flies started to get busy they emitted clicks and other subtle buzzing noises that helped the bats zero in on their distracted prey. Approximately one out of four copulating couples were attacked by a bat, often providing the predator with a hearty meal of two flies, the researchers reported in today’s issue of Current Biology.

“I can only speculate what the original function of this buzzing sound is,” Max Planck Institute for Ornithology researcher Stefan Greif told me. “My guess is that it’s a byproduct of the movements transmitting the sperm. Maybe it’s also easing the female that it really is a male jumping on her, and not a predator.”

So why would the flies choose to mate if it increased their chances of being gobbled up? Well, reproduction is the name of the game in the wild, and flies have only a short timeframe in which they can do it. After hatching from eggs and developing as asexual maggots, the average housefly will live winged and fancy free for just two to three weeks.

Natterer’s bats use the sound of mating flies to help them find their prey / Courtesy: Current Biology

Houseflies are an r-selected species, meaning the populations breed as fast as they can and are willing to take risks doing so. Houseflies endure high levels of predation and other pressures that would take heavy tolls on populations of K-selected species, such as elephants and tortoises, which breed slowly and carefully.

Studies of amphipods, water striders and locusts – all of which are r-selected species – have produced similar results.

“Maybe the cost ‘out in the wild’ is lower than in the cowshed, where we get more predators,” Greif said. “But on the other side, as there are so many flies in the cowshed, overall reproductive success might be so high that it outweighs and counterbalances the evolutionary pressure put on by the bats.”

Copper — invisibility cloak for salmon eaters

Coho salmon lose their trouble-is-a-brewin’ nose when swimming in copper-polluted waters / Flickr: USFWS Pacific

By John Upton

Salmon face a litany of badass predators during their short but meandering lives. After hatching, baby salmon must dodge hungry fish as they swim downstream and into the open ocean. Once in the ocean, they are preyed upon not only by fish and fishermen, but also by sea lions and other marine mammals. After they’ve grown for two to three years, the fish must make the perilous stream run one more time, this time against the current and often into the mouths of waiting bears, in a desperate bid to reach their spawning grounds.

The salmon can’t fight back or use poisons or barbs to defend themselves. Instead, when a predator is near, they lock down, freezing their movements in hopes that they will become invisible to the marauder.

But what happens when the marauder becomes invisible to the salmon? New research suggests that humanity’s wont to pollute has handed such an invisibility cloak to creatures that feast on salmon.

Salmon rely on their keen sense of smell to detect predators. They don’t so much smell the predators, instead they smell a chemical alarm dubbed Schreckstoff that’s released from the shredded bodies of their attacked and battered brethren. But the sense of smell is compromised when the fish swim in water polluted by copper, a common pollutant that flows into streams from mines, farms, buildings and roads.

Washington State University researcher Jen McIntyre set up an experiment to determine whether copper pollution leaves salmon more vulnerable to predators. Into tanks she deposited juvenile coho salmon and a predator species named cutthroat trout, along with Schreckstoff and small amounts of copper.

Salmon that swam in clean water froze in the tanks and managed to escape initial strikes by the trout nine times out of ten. But salmon that were swimming in copper kept blithely on swimming, and they were captured on the first strike 30 percent of the time, often within five seconds.

“They’re not in lockdown mode,” McIntyre said in a statement that coincided with publication of her results in the journal Ecological Applications. “Predators can see them more easily.”

That’s nifty for hungry fish, but not so promising for the populations of salmon that are clinging to survival in polluted waterways around the world.