The speed and efficiency of some insects to consume is legendary. Think of locusts stripping crops bare in hours or days. Utilising these abilities can help us solve problems. Insects can eat food waste that pollutes and emits greenhouse gases and takes up landfill space by converting it into protein and other materials.
Insect protein is already being used to supplement stock feeds in support of industries like aquaculture. For some time now, researchers around the world have also been investigating whether insects might be able to bio-transform our so-called impossible waste, like plastics. And even turn it into something useful.
“Insects are known to detoxify chemicals. It was almost a no brainer to see what they might do with chemistries like plastics,” said Dr Cate Paull, an entomologist with CSIRO. She is leading a multidisciplinary research team investigating the potential of insects to metabolise or bio-transform plastics.
What happens to plastic in the gut of insects?
“No one knew if insects were actually metabolising plastics” Dr Paull said.
“We wanted to see whether the insects can access the carbon from plastic and see how it is used. For example, can they direct that plastic carbon to energise their system and survive? Or are the resulting metabolites (digestive chemicals) their response to a different diet?”
The team originally set out to see whether the insects are actually eating plastic or simply breaking it down into ever-tinier pieces. They hoped to also identify candidate enzymes that could eventually be harvested from insects and used to break plastics down into their constituent elements at industrial scales.
“Stepping back now, it’s likely that understanding the whole gut ecosystem and the suite of activities that are going on related to insect digestion is going to have far greater benefit than just aiming for a single or few enzymes,” Dr Paull said.
The researchers have been on a deep-dive into the digestion of three insect species – the wax moth, mealworm and black soldier fly. They explored what was happening when insects burrowed in and appeared to eat plastic.
Three insects, different plastic types
Three insects were tested with different types of plastic, chosen because they are commonly found in the consumer waste stream. The plastic types were:
- polyethylene and polypropylene both widely used in packaging
- PET, which is clear and lightweight and used in products like juice bottles
- polystyrene
- poly lactic acid, used by 3D printers.
The experiment used the larval stage of the three insect types because as they develop, the larvae do most of the consuming. Adult flies and moths lack mandibles or chewing parts with which to chew on the plastic.
The researchers then examined the plastic, the larvae, and their frass (poo), to see what had changed. The larvae were weighed. Then their metabolites or digestive chemicals were examined to understand whether they were digesting the plastic and what was happening to it.
Using multiple forms of analysis
“We applied a range of technologies for analysis. We were looking at the resulting metabolites, like lipids, and proteins. By putting those layers of information together, we could then start getting a view of what was happening,” Dr Paull said.
Results to date have found that all three insects respond differently to different plastics. For example, compared to the other insects, the wax moth was found to have a distinct suite of digestive chemicals when exposed to polylactic acid. This result warrants further investigation. Ultimately, understanding how specific species of insects metabolise or bio-transform particular types of plastic could allow for the development of fit-for-purpose systems. This would pair specific insect species with particular plastics or waste types and conditions.
“If we take this project as a launchpad we’ve made inroads towards understanding whether or not insects will provide us with answers regarding breaking down plastic. However, it’s quite a lot more complex than we had anticipated!” said Dr Paull.
“This project has initiated and helped support future research in new areas, such as the insect microbiome. Future steps will look at the microbes that are involved in the gut microbiome and the interplay between those and enzymes. And then what you are actually feeding the insect.”
A future where insects are used to separate waste
Scientists are taking on the difficult task of measuring the change to the plastic itself. While this may mean that insects are unable to break down huge piles of plastic, they could still help in other ways. The contamination of other waste with plastics is a major issue, for example.
“We know that supermarkets have a huge problem with plastic wrapped organic material that’s past its expiry date so no longer fit for purpose. But how do you actually separate the plastic from the organic?” Dr Paull said.
“We have been looking at how insects could be used for waste separation. This could transform the organic food waste components to valuable protein and leave cleaner plastic waste for recycling.”
The multi-disciplinary research team at CSIRO is now continuing their investigations to understand the processes of plastic bio-transformation within the three insect species.