Larvae such as those of the black soldier fly (BSF) can form an important new link in circular agriculture. They grow well on unused waste streams such as catering waste or pig manure, which are currently not yet permitted to be fed to insect larvae. This allows us in the future to utilize nutrients that until now ended up in the incinerator. This is the outcome of research by Wageningen Livestock Research. Thanks to a recent amendment to the European law, the larvae can be used as pig or chicken feed.
“One of the missions of circular agriculture is to reduce residual and waste flows,” explains researcher Teun Veldkamp. He works at Wageningen Livestock Research and does a lot of research into the rearing of insects and the application of insect products. “If we can bring lost proteins back into the nutrient cycle, less external protein such as soy is needed. These larvae are true omnivores; they eat almost everything. They are therefore champions in upgrading waste streams that we humans no longer wish to use.”
Veldkamp and colleagues conducted a trial in which they investigated the growth of larvae on different diets: “We used 7 plastic containers with thousands of larvae. In each container different substrates were provided:
- Catering waste (SW, waste from (fast food) restaurants)
- Solid pig manure (PMS)
- Liquid pig manure mixed with chicken feed (PMLCF),
- Digestate (BTFS, a by-product from the sugar industry)
- Olive pulp (OP)
- Roadside silage grass (SG)
- Control group: regular chicken feed (CF)
Each container with a substrate was replicated three times so in total 21 containers with in total 7 substrates were tested.
The results were promising when it comes to catering waste and solid pig manure. The larvae that were fed catering waste even became almost twice as heavy as the control group.
Ammonia and CO2
The researchers also measured the emissions above the containers. This shows a direct relationship with the well or poorly performing waste streams. For catering waste and pig manure, CO2 emissions were high, but ammonia was low. The opposite was true for the underperforming olive pulp and silage grass. “And that makes sense”, explains Veldkamp, “Olive pulp and roadside silage grass are rich in fiber and that is more difficult to digest, even for a larva.”
What is next?
“In summary, it seems that larvae can form an important new link in circular agriculture,” says Veldkamp. “Previous research by my colleague Soumya Kar, for example, has shown that piglets fed BSF are just as healthy, or even healthier than piglets that are fed regular food.
In follow-up research, we looked at how the larvae grew on substrates that differed in chemical composition and also how this affected the chemical composition of the larvae and the frass (combination of insect droppings, larvae skins from the different stages of development, and substrate that remains behind). Publications on this research are still in development.”
This research is part of the Knowledge Base program 34 Circular and Climate Neutral of the Dutch Ministry of Agriculture, Nature and Food Quality. The same ministry finances this research.