Insect left-over substrate as plant fertiliser

The production of insect protein as human food and livestock feed (entomophagy) may provide a more environmentally beneficial alternative to traditional animal agriculture. However, the resulting waste product from insect production has resulted in large accumulations of left-over substrate and frass. Due to its nutrient and microbial profile, this left-over product has the potential to be utilised as a biofertiliser for high value crop production. Studies have been conducted using the frass of various insects (e.g. black soldier flies, houseflies, and mealworms) to monitor its impact on crop productivity. Overall, frass tends to have similar or better results when compared to inorganic fertilisers, especially when combined with them. Aside from productivity and growth, frass may also preserve soil fertility by decreasing leaching and infiltration, and reducing the prevalence of disease and pathogens. In addition, chitin found in frass also has beneficial properties for plant/crop growth and disease resistance. Monitoring the dietary inputs of industrially reared insects may be the best way of mitigating the potential negative impacts of frass application, such as increased electrical conductivity and heavy metal toxicity. No single study confirms all of these benefits at once. Future studies should focus building onto these results by demonstrating systems levels benefits.