bugs that eat plastic -- 4/15/20
Today's selection -- from Buzz, Sting, Bite by Anne Sverdrup-Thygeson. Bugs that eat plastic:
"Every minute enough plastic is dumped into the world's oceans to fill an entire dump truck. At least as much again ends up in landfill sites, and the amounts are constantly increasing. Because we love plastic. It's handy and cheap. We produce and use twenty times as much plastic every year now as we did fifty years ago, and less than 10 percent of it is recycled. The rest of the plastic waste ends up in landfills, in roadside ditches, or in the sea. A report issued by the Ellen MacArthur Foundation estimated that if this continues the sea will contain more plastic than fish by 2050. This is because plastic biodegrades extremely slowly in the natural environment. So the discovery that a number of insects can digest and break down plastic is something of a sensation.
"Take polystyrene, for example. Even if you don't think you use it often, I'm guessing that you've held some in your hand -- if you've ever bought takeout food in a carton or a hot drink in anything other than a paper cup. Because polystyrene, also known as isopore, is the material used to make disposable containers for hot food and drink. In the United States alone, 2.5 billion such cups are thrown away every year -- and we're talking about a material that was thought to be nonbiodegradable. Until now. Because it turns out that mealworms consume isopore cups as if they were part of their regular diet.
"In one study, several hundred American and Chinese mealworms were served some isopore. All of them belonged to the darkling beetle species (Tenebrio molitor), which lives outdoors in most parts of the world and sometimes turns up indoors, too, if any soggy flour residue is left lying in your cupboards for too long. They gobbled up the isopore at record speed, and the larvae raised on this peculiar diet pupated and hatched into adult beetles as normal. Within a month, for example, five hundred Chinese mealworms had gobbled up a third of the 5.8 grams of isopore served up to them. All that was left was some carbon dioxide and a spot of beetle poo, which was apparently pure enough to use as planting soil. There was no difference between the survival rates of larvae that received normal food and those on the isopore diet.
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Mealworms chow down on expanded polystyrene foam and can convert almost half of what they eat into carbon dioxide. |
"But this can hardly be called a superfood. So another experiment compared three different groups: larvae that received isopore, larvae that received some kind of cornflakes, and larvae that received no food at all. The weight of the cornflake-fed larvae increased by 36 percent, while the isopore-fed larvae didn't put on any weight. But they still did better than the poor starving larvae, who lost a quarter of their weight over the two-week duration of the experiment.
"Strictly speaking, the beetles themselves aren't the ones doing the job of breaking down the plastic. For this they rely on some tenants in their gut. If the mealworms are given antibiotics that kill off this gut flora, their ability to break down plastic also vanishes. The breakdown of plastic probably depends on the combined efforts of beetle and bacteria.
"More research needs to be done into whether this insect can help us solve the problem of plastic in the oceans because mealworm beetles aren't keen on getting their feet wet and are hardly suited to the seagoing life. But there is plenty of plastic on dry land that we'd love to get rid of, too, and these beetles may be able to help.
"Mealworms are not alone. Other insects can also help solve the plastic problem. The greater wax moth is a lepidopteran that is viewed as a pest by beekeepers because it eats the wax combs inside beehives. But beeswax has a structure similar to that of polyethylene, which is the kind of plastic used in supermarket shopping bags. And sure enough, it turns out that the wax moth can eat holes in this kind of plastic and transform it into ethylene glycol, a substance we know as antifreeze. Again, this task is not performed by the larva alone but is probably a result of bacteria living inside its gut.
"Researchers are now poring over these findings to discover how we can mass-produce the active substances and perhaps, over the long term, translate this into a practical solution to help us deal with our plastic waste."
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