Black soldier fly larvae (Hermetia illucens) can grow on many types of organic waste. The goal is for the larvae to feed on food waste from both households and large kitchens. Afterwards, they can be used as protein in animal feed or possibly even for human consumption.

But what do the larvae grow best on? New experiments from Aarhus University have shown that the larvae grow best when their diet contains 19.4% protein and when the ratio between protein and carbohydrates is 1:2.8.

Amino acids: The key to growth

We know that humans and animals need protein. Protein consists of amino acids, and some of them are essential for life. These are called essential amino acids and must come from the diet. Since the 1960s, this knowledge has been used to optimise feed for pigs and chickens.

However, our knowledge about the protein and amino acid needs of insects is still in its infancy. The researchers therefore systematically investigated whether the ten amino acids that are essential for humans and other monogastric animals are also necessary for black soldier fly larvae.

The results were clear: If the larvae lacked the amino acids lysine, isoleucine, leucine, phenylalanine, threonine, tryptophan, valine, or arginine, they grew more poorly. The larvae weighed less and had a higher fat content than those that received all the essential amino acids.

The right feed composition 

The study shows that it is not enough just to add protein to the larvae’s feed.

The protein must have the right mix of amino acids for the larvae to grow optimally. If the diet is balanced, it is possible to use less protein.

This makes production cheaper and more sustainable.

This is important knowledge if insect production is to become a real and competitive source of protein for feed and food in the future.

Towards a “food pyramid” for larvae

If only cheap and nutrient-poor waste is used, the larvae grow slowly, and the yield is lower. However, if different types of waste are mixed and perhaps extra essential amino acids are added, larval growth can be optimised. In this way, resources can be utilised better.

The researchers hope that their results can pave the way for nutrient recommendations for insect production – like what we have for pigs and poultry. With such recommendations, producers can mix organic waste and by-products more precisely, so that growth, yield, and sustainability are maximised.

“Our study clearly shows that the balance between essential amino acids is crucial for larval growth and feed efficiency,” says Ida Berggren. She is a PhD student and first author of the scientific article, which has just been published in the Journal of Insects as Food and Feed.