Coffee Beetle Microbes Can Survive on Pure Caffeine

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The coffee berry borer reduces crop yields by more than 80 percent when untreated and causes more than $500 million in damages each year. P. Grebb, USDA, ARS

You may be able to down four cups of joe with only a trembling hand to show. Or perhaps you pride yourself on your ability to drink even more. Six cups? Eight? Big deal. The coffee berry borer laughs at your caffeine tolerance.

That's because this tiny beetle, the most caffeinated creature in the world, lives entirely on the berries of the coffee plant. This is remarkable since the stimulant is an insecticide, toxic to most insects even in small concentrations. The berries the beetle eats, which are dried and roasted before becoming coffee "beans," contain 1 percent pure caffeine, lethal to most bugs and many other animals.

To be anthropocentric for a second, this diet would be equivalent to a human drinking 230 small cups of coffee—containing 23 grams of caffeine—in a single day (this is assuming one eats around 5 pounds of food per day, which is typical for an American). That would kill you, as it's more than double the stimulant's lethal dose of around 10 grams.

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A close-up of the coffee berry borer, Hypothenemus hampei. G. Bauchan, USDA, ARS

But the berry borer (Hypothenemus hampei) does it all day, every day. About the size of a poppy seed, the beetle tunnels into the coffee plant's fruit and lays eggs that grow up doing the same; one berry can produce hundreds of beetles.

Researchers have now discovered how the beetles can survive such a lifestyle: Their guts contain 14 types of bacteria that can not only easily break down the stimulant but also survive solely on caffeine, according to a study published Tuesday in the journal Nature Communications. In the paper, the scientists were able to grow and isolate these 14 bacterial species on petri dishes, which were devoid of any food matter besides caffeine.

"It was totally unexpected to find so many" bacteria that can subsist solely on the chemical, says Fernando Vega, study co-author and a research entomologist at the U.S. Department of Agriculture. "It's cool to finally know, after 100 years of research, how this insect survives on coffee beans."

The tiny beetle, you see, is no miniscule menace: It's the world's most serious coffee pest, creating enormous problems for growers, Vega says. It can reduce yields by more than 80 percent when untreated and causes more than $500 million in damages each year, affecting the income of more than 20 million rural households in the tropics, says Javier Ceja-Navarro, a co-author and scientist at the Lawrence Berkeley National Laboratory.

The beetle first made its way to Brazil in 1913 from the Congo—both coffee and its pernicious pest are native to Africa. Shortly thereafter, it was found in Indonesia, and it has now spread to most of the 80-some countries that grow the crop.

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Coffee grower Gernando Davila looks on as the dreaded borer beetle eats away at his coffee crop in the Alto Mayo valley in northern Peru, April 14, 2004. Leticia Lozano / REUTERS

In the study, the scientists showed that after the beetle's gut microbes were wiped out by a course of antibiotics, it was unable to digest caffeine and couldn't effectively reproduce. However, when the beetles were re-inoculated with one species of bacteria calledPseudomonas fulva (which in one rare instance caused meningitis in a baby girl but is generally not thought to be harmful to humans), they could again metabolize the stimulant. This proved the microbes, rather than the beetle itself, were breaking down caffeine.

"We didn't know anything up until now about the function of microbes associated with [the beetle]," says Mark Wright, an entomologist uninvolved in the work who studies insect pests of tropical fruits and nuts at the University of Hawaii at Manoa. This study is an "impressive" addition to our knowledge on the topic, he adds.

The findings could help scientists find a way of controlling the beetle, although these applications will take a while to develop, Vega says. There are currently no effective, cheap means to deal with for the pest. Removing contaminated beans may help locally but isn't a viable option for a large plantation or region. Spraying insecticides is often too expensive based on the low prices many growers get for their beans. In the mountainous terrain in which coffee grows, it's also logistically difficult or impossible to do, as it involves lots of labor and hauling around heavy equipment. In any case spraying needs to be timed perfectly before the beetles bore into the beans, he adds. Once the insects do that, they are protected, safe in the expansive tunnels they dig therein.

Even when the beetle doesn't put growers out of business, it decreases the quality of beans. The insect "is the worst enemy of quality," Vega notes.

Farmers in Hawaii have had some success using an insect-specific fungal pathogen called Beauveria bassiana to help kill the beetles, Wright says. The product costs about $135 per gallon, though. This may be economically viable in a place like Hawaii where coffee fetches relatively high prices, Vega says, but not so in most of the world.