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How a Tiny Wasp With Invisible Eggs Is Wreaking Havoc on Spain's Chestnut Harvest

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How a Tiny Wasp With Invisible Eggs Is Wreaking Havoc on Spain's Chestnut Harvest
Women gather chestnuts in Spain's Genal Valley. Gary John Norman / Photodisc / Getty Images

The Genal Valley in Southern Spain is famous for its sweet chestnuts, and that could give the economically struggling region a huge boost as vegans and vegetarians in Northern Europe develop a taste for Castanea sativa. But a new threat is putting the valley's reputation, and future, at risk, BBC News reported Tuesday.

"We've lost at least 30% of our usual production," farmer Julio Ruiz told BBC News. "It is all the fault of a small wasp."


The wasp in question is the chestnut gall wasp (Dryoscomus kuriphillus katsumatsu), an import from China that first started causing havoc in the region three years ago. The pest has no natural predators in the area, forest engineer Antonio Pulido told BBC News, and has led to the deaths of numerous trees.

"The main infestation is in the bud where growth is stunted. As a result the flowers and fruit cannot develop and the health and vitality of the tree is compromised. Every variety of chestnut is affected," Pulido explained.

While other crops grow in the valley, the chestnut is the most lucrative, bringing in 10 million euros a year. The wasps have further consequences for the ecology and culture of the area. For one thing, Pulido said, the burning of infected trees to stop the spread is upping the risk of wildfires.

"It is also adding to urban drift as young people in the villages see their future disappearing in front of their eyes," Pulido added.

The chestnuts of the Genal Valley aren't the only ones that have been imperiled by the wasp. The insect has caused damage throughout Europe.

"It is very likely that the chestnut gall wasp population originates from very few females which were accidentally introduced into Italy via infected plant material brought from China in 2006," University of Extremadura researcher RaΓΊl Bonal explained in a press release translated into English and published by ScienceDaily. In a study published in May, Bonal and his fellow scientists found that the wasps present in Europe had all come from a few females reproducing asexually. This allowed the species to spread quickly throughout the continent.

The spread was also aided by the fact that the wasps are only the size of a grain of rice, and their eggs cannot be seen by the naked eye. The eggs are laid in the buds of the trees and begin to develop when the buds open the next spring. As the larvae develop, they cause galls to form on the leaves and shoots of the chestnut trees.

"Since the eggs cannot be seen, people take the infection with them in the seedling and we are taking the enemy home with us. As a result, before selling the plant the nursery should keep it 'in quarantine' for at least one year to ensure that the plant has no galls. In this way the plant sprouts in controlled conditions," Bonal recommended.

In the Genal Valley, government researchers are also considering another solution: introducing the wasp's natural predator, Torimus sinensis. This approach has succeeded in curbing the spread of the wasp in Italy, North America and Japan, and a limited number of them have been released in the Genal Valley already, BBC News reported.

But government researcher Juan-Ramon Boyero Gallardo is also nervous about the repercussions of a wide release.

"The problem of introducing a further exotic species such as Torimus sinensis is that it can invade the natural woodland, attack indigenous species, displace others and alter the overall biodiversity," he told BBC News.

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Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes β€” the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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