Can very hungry caterpillars join the fight against plastic pollution?
Scientists have reported seeing a moth caterpillar commonly bred to provide fish bait eating a notoriously resistant plastic, raising hopes the creature can help manage the global problem of plastic-bag pollution.
The find happened by accident at the home of Federica Bertocchini, a biologist at the Institute of Biomedicine and Biotechnology of Cantabria in Spain, who keeps beehives as a hobby.
“When I went to clean them for reuse in the spring, they were infested with (wax) worms,” the researcher said.
"So I put them in a bag. Then, after a while, I saw the bag was full of holes and these caterpillars were crawling all around my place,” said Bertocchini, the leading author of a study published in the journal Current Biology.
Startled by the caterpillar’s voracious appetite, Bertocchini and a team from Cambridge University decided to conduct experiments to find out just how much, and how quickly, the pests could consume environmentally harmful plastic.
They placed hundreds of the small, yellowish creatures on top of a supermarket plastic bag. Within 40 minutes, holes began to form.
Twelve hours later, the caterpillars had consumed 92mg of the stuff, far swifter than fungus and bacteria would have taken.
Devour plastic bags?
“This discovery could be an important tool for helping to get rid of the polyethylene plastic waste accumulated in landfill sites and oceans,” said Cambridge University professor Paolo Bombelli, co-author of the study.
Polyethylene represents 40% of Europe’s demand for plastic products, mostly in the form of packaging and shopping bags.
Taking many years to biodegrade, these objects constitute a serious hazard for the environment, especially for sea life, when they are not recycled (turtles that mistake them for jellyfish will choke when eating them, while lots of plastic has been found in the stomachs of other sea creatures).
In the European Union, 38% of plastic is thrown out in landfills.
The promising discovery centres on the wax worm – the name for the caterpillar larva of Galleria mellonella, or greater wax moth.
In its pre-caterpillar form, the species is commercially raised as maggots to provide fish bait and aquarium food.
The moth is also a scourge of apiculture, laying its eggs in the precious honeycomb of beehives.
Time for grub?
In their next test, the biologists confirmed that the larvae fully digest a plastic meal, breaking down its chemical components.
Covering a plastic bag with mashed-up caterpillars produced a similar results, suggesting that an enzyme or some other compound was at work.
“The caterpillar produces something that breaks the chemical bond, perhaps in its salivary glands or a symbiotic bacteria in its gut,” Bertocchini said.
The answer may lay in the worm’s habitat and eating habits.
Growing in bee colonies, the moth larvae feed on beeswax, a digestive process that scientists believe may be similar to breaking down polyethylene. “Wax is a polymer, a sort of ‘natural plastic’ and has a chemical structure similar to polyethylene,” Bertocchini suggested.
It remains unclear if a single enzyme or a combination of molecules are responsible for degrading plastic. But biologists hope to identify and reproduce the active agent artificially.
“Using million of caterpillars on top of plastic bags would not be feasible,” Bertocchini said.
Manufactured on a large scale, the plastic-degrading substance would, in theory, take the form of an environmentally harmless liquid that could be used in plastic treatment facilities.
Not so fast
But before celebrating a seemingly simple solution to our polluting habits, we need to step back and realise that nature is much more complex.
An article in The Guardian reminds us of the Australian cane toad debacle – when toads were introduced in the 1930s to control crop pests but instead gorged themselves on other local wildlife and spread across the country.
One problem with this new discovery is that you’d need billions of caterpillars eating all year round to deal with the mountains of plastic waste we produce.
The bigger danger, the article warns, is that these caterpillars come from wax moths – so-called because they eat wax from which bees make their honeycombs, and can thus devastate bee colonies.
With bee populations already under severe stress from pesticides and habitat loss (deforestation), we “might want to think twice about breeding one of their common airborne enemies in huge numbers” – because without bees to help us pollinate crops and trees, agriculture would be in deep trouble.
In short, it’s easier to reduce (or recycle) plastic waste. – AFP