Wageningen University & Research: Residue streams from insect cultivation promising new component of circular agriculture

Is has been known for some time that insects are an excellent source of protein for humans and animals. But that their exoskeletons and other waste from insect-as-food-and-feed production also can have a positive effect on plant growth is still relatively unknown.

‘These residual flows from insect cultivation can – when added to the soil – improve the growth, health, pollination and resilience of plants and promote sustainable crop cultivation,’ says professor of Entomology Marcel Dicke. Together with fellow researchers from Wageningen University & Research and the Netherlands Institute of Ecology (NIOO-KNAW), he discusses the potential of using residual streams from insect breeding in an opinion paper in the journal Trends in Plant Science.

The leftovers from insect production come in two main forms: exuviae, the exoskeletons left behind after molting, and frass, named for the German word for eating, which is “basically insect poop and unconsumed food,” says Dicke.

When added to soil, the exuviae and frass work to promote both plant growth and health. Insect feces is rich in nitrogen, a nutrient that is pivotal to plant growth but is scarce in most soils, and often added to crops with synthetic fertilizer. The insect exoskeletons are rich in chitin, a polymer that is difficult for most organisms to digest.

“There is, however, a set of bacteria that can metabolize chitin, and those microbes help plants to be more resilient to diseases and pests,” says Dicke. “When exuviae are added to soil, the populations of those beneficial bacteria increase.”

New step towards a circular food system
Dicke and his team see the application of insect rearing byproducts to crops as a novel step towards a circular food system in which there is very little waste. The insects are fed waste streams from crop farming or food production, then the insects provide humans with food. Using the leftovers from insect production to bolster crop growth could close this circle. Now, he just needs to get people on board.

More efficient protein production
Insects, which Dicke refers to as “mini-livestock,” are already efficient to farm, especially when compared to more traditional livestock. It takes roughly 25 kilograms of grass to produce one kilogram of beef. The same amount of grass can produce ten times as much edible insect protein. This is due to the higher conversion rate of insects and because up to 90% of an insect’s body mass is edible, compared to only 40% of a cow.

“I have eaten crickets, mealworms and locusts,” says Dicke. “Many people in in our part of the world need to get used to eating insects, but I can tell you that I’ve eaten many other insect species around the globe and I’ve always had a wonderful meal on them.”

Resilience to pests
Going forward, the researchers plan to continue to investigate the potential for exuviae to work as pest control. When a plant is attacked by an insect its leaves can produce volatiles that attract the predators of the pest. “I call it the plant’s cry for help,” says Dicke. “They are recruiting bodyguards.”

Dicke thinks that a similar process may be happening through the plants’ roots and that the microbes that are digesting the chitin in the insect waste might also be acting as security for the plants by breaking down pathogenic fungi and making the plant resilient to pests. “Studies have already shown that microbes associated with the roots help plants by protecting against diseases,” says Dicke. “Now we’re investigating whether plant roots recruit microbes that help them in defending against pests.”

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