Plastic fantastic: it’s a gut feeling for caterpillars

A very hungry caterpillar could help to tackle the problem of plastic pollution, a study suggests.

Caterpillar at Koah. Picture: Amanda Johnston

A very hungry caterpillar could help to tackle the problem of plastic­ pollution, a study suggests.

Scientists found that the larvae of the greater wax moth can eat polyethylene, one of the most widely produced plastics.

The ­research suggests that the caterpillars — or possibly the bacteri­a in their gut that allows them to live on a diet of plastic bags — could be harnessed to break down such waste within days, accelerating a process that would otherwise take centuries.

In the wild the caterpillars, known as waxworms, infiltrate bee hives and consume the beeswax that forms the honeycomb. Low-density polyethylene, used to make bags, has a similar molecular structure.

Scientists have found that 60 ­waxworms could consume more than 30sq cm of plastic sheeting in a week.

“They are really avid ‘plastivores’,” said Christophe LeMoine of Brandon University in Canada, who led the study. “We think it is quite phenomenal that these insects are able to survive for weeks on a diet made entirely of plastic.”

More work is needed to understand how the caterpillars and the microbes in their digestive tract work together. One challenge could be handling the substances the larvae excrete when fed ­plastic, which appear to include ethylene glycol. It can be used as a raw ­material to produce polyester ­fibres, to make fibreglass and for antifreeze, but is also toxic.

The amount of plastic debris in the ocean is forecast to rise from 50 million tonnes in 2015 to 150 million tonnes by 2025, accordin­g to a British government report published last year.

One approach to tackling the problem has focused on using living organisms, including bacteria and fungi, to alter and break down the chemical structure of polyethylene and other plastic polymers.

For a study published in the journal Proceedings of the Royal ­Society B, Dr LeMoine’s team ­explored the role of the waxworm’s gut bacteria. It found that when the caterpillars were treated with antibiotics to reduce the number of microbes in their gut, they were not able to degrade polyethylene as easily. In ­addition, when caterpillars were fed exclusively on polyethylene they had more gut microbes than ones fed on a normal diet.

The researchers also discovered that certain gut bacteria could survive being fed only plastic for more than a year. Under these conditions, however, it took longer for the plastic to be broken down than when the larva ate it.

“There appears to be a synergy between the waxworm and its gut bacteria that accelerates plastic biodegradation,” Dr LeMoine said. “A better understanding of how this works may guide future efforts to design the ‘perfect’ ­plastic biodegradation system.”

The Times