How a Tiny Wasp With Invisible Eggs Is Wreaking Havoc on Spain's Chestnut Harvest
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 tiny chestnut gall wasp..latest article from FR http://t.co/7ZwYBjj1F6 http://t.co/xBdavy42M0— Forest Research (@Forest Research)1444904054.0
"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 Raúl 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.
Oriental Chestnut Gall Wasp - Dryocosmus kuriphilus - twig tip and leaf galls found at Greenwich @theroyalparksr -… https://t.co/2RXAOvgHai— 🐝 NHM Bees 🐝 (@🐝 NHM Bees 🐝)1523198161.0
"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.
Invasive Tick Spreads to Ninth State, CDC Warns of 'New and Emerging Disease Threat' https://t.co/9r4yqpJvxJ— EcoWatch (@EcoWatch)1543820052.0
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A Game of Jenga<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>
Cutting Off Circulation<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>
The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
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