Insects are considered a possible protein source of the future. The larvae of the black soldier fly in particular are often mentioned as a climate-friendly alternative to meat or soy because they can produce high-quality protein from waste materials. But how sustainable is the production of these insect larvae actually? A research team has now examined this in more detail.
The larvae of the black soldier fly (Hermetia illucens) contain high-quality protein that is comparable in quality to soy protein. They can also grow on very different biomass sources, including by-products and residues from agriculture and food processing. Experts therefore see great potential in the fact that these larvae could contribute to more sustainable protein production in the future. However, how environmentally and climate-friendly the raising of larvae is has so far hardly been investigated.
It depends on the food
A research team led by Manfred Mielenz from the Research Institute for Livestock Biology in Dummersdorf has now systematically addressed the question for the first time. The researchers examined how the quality and nutrient composition of the fed biomass affect the growth, body composition and gas emissions of the insect larvae. The continuous measurements of the gas emissions of carbon dioxide and ammonia were carried out in a sensitive phase of larval development, namely between the ninth and 16th day after hatching.
The result: which gases are produced during rearing depends heavily on the quality and nutrient composition of the feed. If the substrate is difficult to digest or poor in nutrients, the larvae grow more poorly and produce less protein – at the same time, CO₂ emissions increase. With more nutrient-rich biomass, however, the larvae develop significantly better. However, towards the end of the growth phase, increased ammonia emissions may occur under such conditions. This is probably related to an unbalanced ratio of protein and energy in the feed.
Climate balance only with an overall view
How these emissions are assessed is therefore also crucial. “Emissions can only be meaningfully classified if they are related to the actual output – for example the protein content or the dry mass of the larvae,” explains Mielenz. “Higher absolute emissions do not necessarily mean a worse carbon footprint if emissions per unit of high-quality protein produced are lower.” A first rough classification suggests that, based on the amount of protein produced, the CO₂ emissions of the larvae could be lower than those of cattle or chickens. However, the researchers emphasize that this is only an initial estimate and further studies are necessary.
The study now provides quantitative emissions data for the first time and also shows how feed substrates can be composed in such a way that fewer emissions are generated during the production of insect protein and larval rearing becomes more efficient. However, an examination of larval rearing alone is not sufficient for a final assessment of emissions, as the researchers emphasize. The entire life cycle for the insect protein from soldier flies is crucial – including the production of feed substrates and the handling of remaining residues after the growth phase. Nevertheless, these and other studies suggest that insects can help produce animal protein more sustainably in the long term.
Source: Research Institute for Livestock Biology; Specialist article: Bioresource Technology, doi: 10.1016/j.biortech.2025.133812