When was the last time you threw out a mouldy, stale or rotten piece of fruit, a loaf of bread, block of cheese or meat? This type of food waste, called consumption waste, is only one in a chain of organic waste production. Even before food reaches your home, large amounts of waste are generated. In South Africa alone, it is estimated that over 8.6 million tonnes of this 'pre-consumer' waste is generated each year. That is approximately 170kg for each person in South Africa in a year.

Food waste is bad for the environment and food security. It means that scarce water and nutrients used to produce food are lost, excessive amounts of pesticides are used, more greenhouse gas emissions are released into the atmosphere than needed, and ultimately, less food reaches hungry people. As it decays, food waste contributes to greenhouse gas emissions, pollutes surface and groundwater, produces odours, and attracts pests. Food waste also adds to the cost of food for consumers because the extra resources needed to compensate for those losses need to be covered by farmers, fresh produce markets and supermarkets. These problems are so big that the United Nations has declared 29 September the International Day of Awareness of Food Loss and Waste  (#FLWDay) each year.

But solutions are being developed. For example, at the University of Pretoria's Department of Zoology and Entomology, a team of researchers is working with industry and using their knowledge of insects to help address the problem of pre-consumer food waste. They are also generating useful products that then support further food production.

Fully developed black soldier fly larvae ready to be separated from degraded fruit and vegetable waste. Image: Nina Parry

Waste bioconversion is the process of retrieving nutrients from waste using living organisms. Pre-consumer food waste is high in nutrients and is a natural resource used by insects to breed. Insects feed on the waste, helping to reduce it while taking nutrients into their bodies. After insects have finished feeding on food waste, they are rich in protein and fats. The insects can be harvested and processed into food additives for livestock like chickens, pigs and farmed fish. They can also be processed further to extract the oils to produce biodiesel and produce other chemicals used in the beauty, health and wellness industries.

Professor Chris Weldon, an Associate Professor in Applied Entomology, and several of his students are working out whether flies can be used in bioconversion. He says that "flies are normally associated with different types of organic waste, so that means they are ideal candidates for bioconversion". Large amounts of pre-consumer waste are produced, so Prof Weldon's group is also searching for the best ways to breed the vast numbers of flies needed to feed on and convert the waste.

They have found that blowflies may be helpful in bioconversion. Blowflies are the metallic blue, green and brown flies that you might see around your home. Prof Weldon and his team found that "blowflies are easy to breed, multiply fast and can very effectively convert meat processing, fruit and vegetable waste into their body tissues. Meat processing waste is a particular problem because it tends to be not degraded well by other insects used for bioconversion".

Another type of fly, called the black soldier fly, is also used for bioconversion. Prof Weldon says that "the black soldier fly is already being used in commercial bioconversion facilities, but a lot still needs to be known about how to ensure consistent rates of waste reduction and fly output and quality". Working with a bioconversion facility near Centurion in Gauteng, South Africa, they now know what female black soldier flies like to lay eggs on. They also know the best time to harvest black soldier fly larvae, the right blend of waste to achieve the best levels of waste reduction and larval production, and how to best dry the larvae for processing into animal feed.

Prof Weldon knows that there is still a lot left to do. However, he says, "there are more flies that can be tested as candidate bioconversion agents. For the already promising flies, we need to work out the best way to breed them at large scales. There is also the potential to combine different insects in optimal blends for livestock feed".

Eventually, the work being done by Prof Weldon and his students in the Department of Zoology and Entomology will help to reduce food waste going to landfills and make food more affordable. In addition, they will retrieve nutrients from food waste and redirect them back into food production systems. Thus, he says, "we are trying to create a circular economy, closing the loop between food waste and food production, and being able to feed more people more efficiently".

Interested in entomology?

What is entomology?
The scientific study of insects.

What is applied entomology?
It is the use of knowledge of insects to benefit humans. This includes working out the best way to control insect pests, helping to promote crop pollination by insects, and identifying insects that indicate environmental health. Furthermore, it includes using insects to rehabilitate degraded land like former mine sites and solving criminal cases using insects on bodies as evidence.

How can I become an entomologist?
Register for the BSc Entomology degree at the University of Pretoria!

Is there work as an entomologist?
BSc Entomology graduates are highly sought after by the agriculture industry and government agencies, particularly to work on pest detection and management. Postgraduate study in entomology at honours or higher levels opens more opportunities with higher levels of responsibility, involvement in solving entomological problems and higher salaries.