That "Fresh Cut Grass" Smell Is a Distress Signal

inga/iStock via Getty Images
inga/iStock via Getty Images

Trauma, that’s what. It’s the smell of chemical defenses and first aid. The fresh, “green” scent of a just-mowed lawn is the lawn trying to save itself from the injury you just inflicted.

Leafy plants release a number of volatile organic compounds called green leaf volatiles (GLVs). When the plants are injured, whether through animals grazing on them, you cutting or mowing them, or even just unintentionally rough handling, these emissions increase like crazy.

The rush of chemicals does a few things. Some of the compounds stimulate the formation of new cells at the wound site so it closes faster. Others act as antibiotics that prevent bacterial infection and inhibit fungal growth. A few spur the production of defensive compounds at un-wounded sites as sort of a pre-emptive fortification. And still others react with other chemicals to act as something like distress signals. Scientists found in one study that the saliva of certain caterpillars reacts with the GLVs released by coyote tobacco plants to make them attractive to the "big-eyed bugs" that regularly eat the caterpillars.

Thankfully, the mix of lawnmower blades and GLVs won't get you eaten. Instead, humans get a treat. Among the GLVs released by damaged grass are a group of eight related oxygenated hydrocarbons, including aldehydes and alcohols, that cause the “green odor.”

There may be a high cost to that wonderful smell, though. These compounds are precursors to ozone formation, according to Australian researchers, and can contribute to the formation of photochemical smog in urban areas.

Pandemic vs. Epidemic: What’s the Difference?

If scientists can't develop a vaccine for a new virus quickly enough, an epidemic can turn into a pandemic.
If scientists can't develop a vaccine for a new virus quickly enough, an epidemic can turn into a pandemic.
doble-d/iStock via Getty Images

As the new coronavirus continues to spread around the world, the words epidemic and pandemic are showing up in news reports more often than they usually do. While the terms are closely related, they don’t refer to the same thing.

As the Association for Professionals in Infection Control and Epidemiology (APIC) explains on its website, “an epidemic occurs when an infectious disease spreads rapidly to many people.” Usually, what precedes an epidemic is an outbreak, or “a sudden rise in the number of cases of a disease.” An outbreak can affect a single community or several countries, but it’s on a much smaller scale than an epidemic.

If an epidemic can’t be contained and keeps expanding its reach, public health officials might start calling it a pandemic, which means it’s affected enough people in different areas of the world to be considered a global outbreak. In short, a pandemic is a worldwide epidemic. It infects more people, causes more deaths, and can also have widespread social and economic repercussions. The spread of the Spanish influenza from 1918 to 1919, which killed between 20 and 40 million people around the world, was a pandemic; more recently, the H1N1 influenza created a pandemic in 2009.

Here’s where it gets a little tricky: There’s no cut-and-dried classification system for outbreaks, epidemics, and pandemics. Based on the definitions above, it might seem like the current coronavirus disease, now called COVID-19, falls into the pandemic category already—according to a map from the World Health Organization (WHO), there are more than 80,000 confirmed cases in 34 countries, and nearly 2700 people have died from the disease. It’s also beginning to impact travel, stock markets, and the global economy as a whole. But WHO maintains that although the situation has the potential to become a pandemic, it’s still an epidemic for now.

“It really is borderline semantics, to be honest with you,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN earlier this month. “I think you could have people arguing each end of it. Pandemics mean different things to different people.”

[h/t APIC.org]

Fat Bats Might Be Resistant to Deadly White-Nose Syndrome

Penn State, Flickr // CC BY-NC-ND 2.0
Penn State, Flickr // CC BY-NC-ND 2.0

Good news for flying mammals: chubby little brown bats might be genetically resistant to white-nose syndrome, a fungal disease that’s killed more than 5.5 million bats since it was first documented in 2006 [PDF]. A new study in the journal Scientific Reports describes three genetic adaptations in the bats that could protect them from the pathogen.

Little brown bats (Myotis lucifugus), common in Canada and the eastern United States, are especially susceptible to white-nose syndrome. According to lead author Giorgia G. Auteri, a doctoral candidate at the University of Michigan, white-nose syndrome kills bats by disrupting their hibernation cycles.

“When they’re in hibernation in the winter, they’re not meant to be waking up. They’re supposed to be asleep,” Auteri tells Mental Floss. “But this fungus grows on them, and it causes the bats to keep waking up during hibernation. And because they’re waking up when they shouldn’t be, they’re running out of fat reserves too early.”

But while white-nose syndrome has devastated bat populations in North America, not all infected bats die from the disease—some recover. Auteri wanted to find out what made the survivors so special.

Auteri and her team compared the genetic makeup of nine surviving and 29 non-surviving little brown bats from northern Michigan. They discovered that survivors share three important genetic distinctions. “One is involved with fat metabolism,” she says. “And another is involved with regulating when the bats wake up from hibernation. And the third gene is involved in their echolocation ability, in their sonar for hunting insects.”

The results make sense, Auteri says. Because white-nose syndrome interrupts bats’ hibernation schedules, bats with genes that relate to more optimal fat storage (i.e., they’re fatter) and better hibernation regulation (i.e., they sleep longer) are more likely to survive the disease.

Auteri’s research could help scientists and conservationists find ways to preserve little brown bat populations. Besides being adorable, little brown bats also play an important ecological role as predators of insects like mosquitoes, moths, and other pests that are destructive to crops and forests.

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