The wax worm is a parasitic caterpillar that munches its way through beeswax and causes considerable harm to man-made bee hives. This pest, once notoriously infamous is now becoming popular for all the right reasons – after a discovery that suggests that the greater wax moth, Galleria mellonella digests plastic!
Federica Bertocchini is a biologist from the Institute of Biomedicine and Biotechnology at Cantabria, Spain and also, an amateur bee-keeper. One day while looking at her beehives, she noticed that they were infested with caterpillars called wax worms. These are well-known pests that voraciously feed on the wax produced by bees to build their honeycombs. She isolated them and kept them in a bag while cleaning the hives.
After some time, she noticed that the plastic shopping bag was infested with holes and the caterpillars were meandering all over the place. She rounded them up and identified them to be larvae of the greater wax moth,Galleria mellonella, a well-known pest of bee hives.
“This project began there and then,” she said.
A timelapse of worms eating polyethylene and escaping from a plastic bag. Credit: César Hernández/Ainhoa Goñi
Dr.Bertocchini teamed up with Dr.Paolo Bombelli and Dr. Christopher Howe from Oxford University to confirm if this waxmoth, Galleria mellonella could indeed bio-degrade plastic or polyethylene and produce ethylene glycol- the breakdown byproduct.
The trio decided to focus on polythene or polyethylene, as it is the most common packaging plastic, found in garbage dumps.
To ensure that the worms were actually digesting the plastic and not merely chewing it, the team pureed a few of them, and applied the resulting paste to plastic/polyethylene. After 14 hours, the team observed that 13% of the plastic was gone, suggesting that the wax worm was producing something that actually digested the plastic.
When scanning the chewed-up bags for residue using FTIR analysis, they found ethylene glycol—the main compound in antifreeze—further confirming polyethylene degradation.
When a polyethylene film was left in direct contact with wax worms, holes started to appear after 40 minutes, with an average of 2.2 holes per worm per hour. It took almost 12 hours for these caterpillar to consume 1mg of a shopping bag, when the standard weight of a shopping bag is approximately 3gms. That means, it would take over hundred worms, a month to completely degrade one small shopping bag.
Several strategies have been employed in the past, to use live organisms to digest plastic but to no avail. A bacterium known as Nocardia asteroids was found to be the closest contender to the wax worm. This bacterium took more than six months to degrade half a millimetre of plastic, compared to the wax moth that took only 40 minutes to chew up the same amount of plastic.
It is not clear however, if it’s the insects themselves or some bacteria in their gut that produces these polythene-degrading enzymes. “If I had to guess, I would suspect the bacteria,”says Jennifer DeBruyn from University of Tennessee, who is also working on plastic-degrading microbes.
The team is working on further analyzing whether it is the gut bacteria in the worms, or the worms itself that is doing the trick. Whatever be the case, the fast rate of biodegradation reported here, could have potential environmental applications in future.
Worldwide, a trillion single-use plastic bags are used each year, nearly 2 million each minute. World governments are waking up to this issue of plastic waste and the need for safe disposal. At least 16 African countries have announced bans on certain types of plastic bags and many other countries are planning to follow suit or impose taxes.